Bulletin No. 235 Series I B> DescriPtive Geology- 4l

\ D, Petrography and Mineralogy,

DEPARTMENT'OF THE INTERIOR

UNITED STATES GEOLOGICAL SURVEY

CHARLES \). WALCOTT, Di HECTOR

GEOLOGICAL RECONNAISSANCE

ACROSS THE CASCADE RANGE

NEAR THE FORTY-NINTH PARALLEL

GEORGE OTIS SMITH AND FRANK C. CALKINS

WASHINGTON

GOVERNMENT PRINTING OFFICE

1904
Trri-o^)

SL'BD
C 0 N T E N T S.

I'lliJO.

Letter of transmittal. ---_--_---..-.._-_.____.._-______._....._.._____.._.. 9

Introduction-__-._.__,.__-.----._--._._.__..._....__....---_--__._.__.-.-_- 11

Scope of report ---.--_.____.._______-.--....._---.._...._.__ ._.- 11

Route followed ........................:......................... 12

Geography .............................................................. 12

Topography .......................................................... 12

Primary divisions of the region..--.........-.--.-.--.-.-.. 12

Okanogan Valley .................:.. ............................ 18

Cascade Range ...............:........,..._ ....^......i........ 13

General characteristics..._.....-.....-..----.--.----.-.-..-.. 13

Northern termination.,.---.....-......--.-.............._ 13

Subdivision .............................................. 14

Okanogan Mountains ........................................... 14

Hozonieen Range ............................................ 15

Skagit Mountains....-.... ......-.----....-.-----..-...--.--- 16

Drainage ..................................................... 17

Climate ...................................................... ...... 17

Roads and trails -.-------.---..-.-..-.-.-..-..--.-..---.....-.--...---- 19

............................................................... 20

Description of formations ...--..............-.-....--.-------.-.--... 20

Classification and mode of treatment .......-.-.---....-.---.. 20

Pre-Cretaceous rocks................------.-.-.--.--.--....---... 21

General character and distribution ..... , ..................... 21

Columbia and lower Okanogan valleys........................ 21

Upper Okanogan Valley ..._.........---.-.--. ................. 22

Basin of upper Skagit River.. ................................ 28

Lower Skagit Valley --...-----.-.------.....-----.-.-.-...---- 24

Mount Baker district ................................... ..... 25

Preliminary statement ..............................'..... 25

Supposed Paleozoic rocks ..-....-----.-----..----.---....- 26

Supposed Mesozoic rocks ............_..-.-.-.-......--... 27

Volcanics near Hannegan Pass ..........-. .---...--...... 27

Cretaceous strata ................................................. 28

Pasayten formation ............\................. ........ .... 28

Occurrence............................................... 28

Name ................,..'................................: 29

Lithologic character and thickness ....._-.-.'-.--.--...... 29

Tertiary formations.-----..-.-.....--...-..-..-..-.--------------.. 30

Classification and distribution.............-..-.-...-..----.-. 30

Columbia River Valley. ........................................ 30

Swauk formation ...............-..........--.----.----..-- 30

Andesite and rhyolite ..^................................. 31

Yakima basalt.....'........................-.---.--.----. 31

3
4 CONTENTS. '

Geology Continued. Page. 

Description of formations Continued. 

Tertiary formations Continued.

Okanogan Valley ..--.....-.-..-.----.-.-.-. ..----.--...--.-- 32

Volcanics east of Hidden Lakes.-.----_--..------------------. 33

Western slope ..............1..........:...................... 34

Hamilton district............................ .."..... .. .--.. 34

Nooksak Valley..... -.-.....---.......-I................ 34

Quaternary formations.--......--....--....-.-. ..--.-----..----.. 34

Classification and distribution,............................... 34

Mount Baker lava ............................................ 35

Geologic relations .....'.-.-..--..............--..-...-..'-. . 35

Lithologic characteristics .... ---..--..-.... ............ 35

Glacial and stream deposits --..------..-...-_.......-...-..-. 35

Columbia and Okanogan valleys.......................... 35

Mountain area _.................'.......................... 41

Western area __....._....__..._____.!.^_................I. 42

Intrusive rocks _-.-....--...----...--.--......---.....-.......... 43

Preliminary statement.....--...-----...-.................... 43

General classification.........- -.-.......-....---.......... 43

Method of treatment ...'............ ...................,.... 44

. Along the Columbia.......................................... 44

Megascopic features of granodiorite L...-.-................ 44

Occurrences of.granodiorite...---... -.-.-................ 45

Okanogan Valley..'........................................... 45

 Granitic and dioritic rocks ............................... 45

Gabbro and diabase near Loomis ............-.---....--.. 46

Okanogan Mountains.....-.......-.--.....-.....-..-...--.-.. 47

Ultrabasic intrusives of Mount Chopaka.................. .47

Composite character of the granite belt_.................. 47

Biotite-granite ..-....--...-. 1 -.-.'.--............... 1..... 47

Granodiorite-.-....-...--..-...-.-.--...-....-----....--- 47

Diorite of the Horseshoe.................................. 48

Biotite-muscovite-granite ................................ 48

Hozomeen Range -..---.--.--..--.--.......-.......--...---... 49

Quartz-diorite.. ........--..-.-------...-.-- ------........ . 49

Serpentine (saxonite) ...-...--.-----.--------------------- 49

Dike rocks-.-.....-........-.....-----....-.........-..... 49

. Skagit Valley and Skagit Mountains.. ...... ^.................. 49

Eastern portion.......................................... 49

Western portion -....-.--...........'.................'...,. 50

Petrography ................................................^........ 51

Introductory statement. ............^...................... ...... 51

Metamorphic rocks ...--....-.---.-.-..........--.-.---......--.-. 52

Altered basic lava near Loomis_....--.............---.-.-.-.. 52

Schists of Skagit Valley ...................................... 53

Chloritic schists.- __.__.'-_______-..__.-.-.._____-__"..__--. 53

Glaucophane-schists. - ..........^......................... 53

Volcanic rocks .;.',-.--....-;'-.--....-.._.. ...--.-..- ...---...---- 54

Distribiition and classification .............."..........-.-..... 54

Rhyolites -.....-.--.----------....----_-..--...----.-.-..-.-.- 55

Soda-rhyolite near Wenatchee...............:..-..-...... 55

Soda-rhyolite near Clover ...'.,....... r .^.......,....,..... 56
CONTENTS. 5

Geology Continued. . Pl^ePetrography Continued.

Volcanic rocks Contimied.

Andesites.....-..--.-...;--..--.....-...-...--.----.----.--.-. 56

Dacite.._..____.--.-._-___-----_..-----.-.--------..------ 56

Hornblende-pyroxeue-andesite...._---.-_-.--..-----.--.--- 56

Pyroxene-andesite of Mount Baker .......1............... 57

Basaltic augite-andesite .....--.-..-........----....-.-.-. 59

Pyroxene-andesites of Skagit Valley and Sank Mountain .. 60

Basalts,..........-.-.-..-...-..-................-."------------ 60

Hypersthene-basalt .--.-.--.....-----'...-:.----.--.--.--. 60

Yakima basalt -___....__..._ ..___..____.._... ...--..--..-.- 60

Metabasalts. _._.._._. _._..___.___._.._.__..---.---- .---.. 61.

Plutonic rocks..-..-...-.--.-.-..---..----..._.....--..----...-.-. 61

Distribution and classification ______._.________.__--._---..---. 61

Granites.......................... ...................... .. ...... 62

Biotite-muscovite-granite of Mount Renimel type......... 62

Classificatory position.........................-.-..:..... 68

Biotite-muscovite-granite of Okanogan Valley type........ 68

Biotite-granite ............_..........._....r _............. 65

Granodiorites-................................................ '66

Acidic granodiorite of Mount Baker district .............. 66

Basic type of granodiorite ................. .^............ 67

Diorites ............................................. .....^... 69

Quartz-mica-diorites---------_--------.-.----.--..- ------ 69

Quartz-pyroxene-mica-diorite ..........._.......---_....... 70

Quartz-augite-mica-diorite'..-.-.----..-.------..-.--...-. 70

Gabbros ..-.--...-..-..-- .......-.-.-...-......--....-. ...... 71

Olivine-hornblende-gabbro ..................-..-....._... 71

Uralitic gabbro of Palmer Mountain -.....-...---.'........ 72

Uralitic gabbro of Mount Chopaka ... ...'................ 72

Ultrabasic rocks .^............................................ 73

Serpentines and pyroxenites of Mount Chopaka ........... 73

Saxonite of Ruby Creek .____...__..._..__...--_.,-..___._. 73

Hypabyssal rocks. .................................................. 73

Classification and distribution.........--.-....-..-.-.--...... 78

Acidic dike rocks --.-----.-..----.-.--..-..........--........ 74

Granophyre ............................................... 74

Granite-porphyries ..... ...........'...................... 75

Pegmatites ........................... ....-'............. 75

Aplites ... ......-.----.--...---.-..-..-.--..--.-.-..--..-.. 76

'' Soda-syenite ".......................................... 76

Lamprophyric dike rocks -...-.-..---..--...... -..--......... 76

General characteristics. ......:........^................... 76

Diorite-porphyries .............'...........-.............. 77

Hornblende-porphyries................................... 77

Diorite (?) of Granite Mountain ........................... 78

Diabases........------.-----.-.-....- _._._-_:.._._______. .79

Peridotite ................................................. 79

Conclusions ...................................... ......---.._.... 79

Preliminary statement ............................ .....i...... 79

Evidences of marginal differentiation._....................... 80

. . Columbia River Valley.-.................................. 80

Granite Mountain _.__________..____ __.___________.______ 80
6 CONTENTS.

Geology Continued. , Page. 

Petrography Continued. 

Conclusions Continued.

Relationships and general chemical characters of the igneous

rocks_._..__...-------_--'------_--------------------_-_-----. 81

Structure................--..-..-.-.-._---.-.---.--._.-...-.....--.-. 84

General features.....-..--...-....._. .....-----------..-..... 84

Folds in the Pasayten formation ....--.-...---.........-..--. 84

Structure in the Mount Baker district__.__-----..-.-.__------. 85

Physiography..................................... ...--.--.--.----..._ 85

Scope of discussion ..........-..-...-.....----------.._..--.. 85

Recognition of a peneplain surface ................'............ 86

Physiographic subdivision of Cascade Range --.-..........-.. 88

Relation of Cascade Mountains and interior plateau........... 89

Glacial sculpture .............. 1.....................:........ 91

Coulees...................... T ..................................... 92

Resources ....L............................................................ 93

Agriculture ........__..-......................-...._...._.-._... 93

Forests..-.........--......-.--..-...---.--.-.,-.'.---..--.-.----.- 94

Gold and silver .................................................. 94

Eastern districts .......................r ..................... 94

Mount Baker district ..--...---....--......-- --.....-...----.. 95

Coal.............................................................. . '97

Index ............ 1..................................................... 99
ILLUSTRATIONS.

Page.

PLATE I. Reconnaissance map of Cascade Range near the forty-ninth

parallel __.__.__.._..._..___.._________'___._____.--..._-...-.._.__ 1.2

II. A, Tertiary sediments, Squantl Falls, Similkanieen River, Washington; B, Cretaceous conglomerate forming crest of Hozomeen 

Range, head of Three Fools Creek, Washington............... 28

III. A, Amphitheater Peak, Okanogan Mountains, Washington, sculp-^ 

tured by glacial cirques; B, Cathedral Peak, Okanogan Mountains, Washington ....................-.....--..-..--.-..--.. 88

IV. A, Interior plateau of British Columbia, as seen from Bauernian 

Ridge, Okanogan Mountains, Washington; B, Rugged topography near forty-ninth parallel, looking north from Bear Mountain , Mount Baker mining district, Washington..... n........ 90

FIG. 1. Plateau representing tiplifted lowland surface; western portion of 

Skagit Mountains, with Mount Baker; looking west from Bear 

Mountain...................................................... 87
I

,4,
LETTER OF TRANSMITIA

'DEPARTMENT OF THE INTERIOR,

UNITED STATES GEOLOGICAL SURVEY,

Washington, D. C., March 17, 1904.

SIR: I have the honor to transmit herewith the manuscript of a 

paper entitled "A Geological Reconnaissance across the Cascade Range 

near the Forty-ninth Parallel," by George Otis Smith and Frank C. 

Calkins. The report embodies the geologic results of field work during the season of 1901 in connection with the northwestern boundary 

survey. I recommend its publication as a bulletin. 

Very respectfully,

C. W. HAYES, 

Geologist in Charge of Geology. . Hon. CHARLES D. WALCOTT,

'Director 'United States Geological Survey.

9

A GEOLOGICAL RECONNAISSANCE ACROSS THE CASCADE RANGE NEAR THE FORTY-NINTH PARALLEL.

By GEORGE OTIS SMITH and FRANK C. CALKINS/

INTRODUCTION.

SCOPE OF REPORT.

In 1901 three geologic parties were assigned to the reconnaissance 

of the northwestern boundary. The duties of these parties included 

not only the geologic and economic investigation of .a strip of country 

in the vicinity of the forty-ninth parallel, but also the examination of 

the area with special reference to the condition of the monuments on 

the international boundary. The results of the surveys made by 

them are incorporated in a joint report to the Superintendent of the 

United States Coast and Geodetic Survey and the Director .of the 

United,States Geological Survey.

The party assigned to the western section, from Osoyoos Lake, in 

northern Washington, across the Cascade Mountains to the coast, was 

in charge of George Otis Smith, with Frank C. Calkins as assistant 

geologist. While the major portion of the work was topographic and 

connected with the examination of the boundary, considerable general information was obtained regarding the geology of the region 

traversed. Only a portion of such data is contained in the report 

mentioned above, and it has seemed advisable to place the results of 

the reconnaissance in a form in wjrich they will be available for 

reference.

The region in the vicinity of Barren has been described by Prof. 

I. C. Russell, 6 but there is no literature containing geologic descrip-

« This report is based upon the field observations of both authors. The work near the boundary 

was roughly subdivided, Mr. Smith taking the territory immediately adjacent to the boundary, 

while Mr. Calkins examined the area farther to the south. The larger part of the "Description 

of formations" was written by Mr. Calkins. The chapter on "Petrography" was entirely the 

work of Mr. Calkins, by whom the laboratory study of the rock specimens was pel-formed. The 

remainder of the report, except a part of the notes on coal, was written by Mr. Smith.

^A preliminary paper on the geology of the Cascade Mountains in northern Washington: 

Twentieth Ann. Kept. U. S. Geol. Survey, pi. 2,1900, pp. 83-210.

11
12 CASCADE KAKGE NEAE FORTY-NINTH PARALLEL.

tions of the northernmost part of Washington other than the reports 

of the geologists connected with the boundary commissions, 1857-1860. a

ROUTE FOLLOWED.

The party outfitted at Ellensburg, AVash., the latter part of June, 

1901. The route by which the forty-ninth parallel was reached was 

practically the same as that used at the time of the earlier survey of 

the boundaiy, crossing Table Mountain to the mouth of the Wenatchee and thence northward along the west bank of Columbia and 

Okanogan rivers.

Work was commenced in the vicinity of Lake Osoyoos July 10, and 

the reconnaissance extended west until October 5. The route taken by 

the pack train is indicated on the map. Until the valley of the Pasayten was reached it was found possible to keep within a few miles of 

the forty-ninth parallel. - Here, however, a detour southward was 

made to the mining camp, Barron, whence we proceeded down Slate 

and Ruby creeks to Skagit River.

A side trip was made on foot up this river over the abandoned Fort 

Hope trail. Direct access to the mountainous country west of Skagit 

Valley being out of the question, the trail down the Skagit from Ruby 

to Marblemount was followed, and thence country roads were traveled, by way of Sedro-Woolley and Deming, to Maple Falls, on the 

North Fork of the Nooksak. This river was followed as far east as 

Hannegan Pass and the boundary line visited on Silicia and Turnmeahai creeks. The approach of bad weather did not permit a trip 

to the head of Chilliwhack Lake, so that the region between Silicia 

Creek and Skagit River was not visited.

The route followed from Ellensburg to Osoyoos Lake afforded opportunities to roughly extend the observations made in central Washington during previous years, and thus to connect in some degree the

areas that have been mapped in detail for folio publication with the 

boundary section. In lower Skagit Valley connection Avas also made 

with the route followed by the senior author in 1895 in the course of a 

reconnaissance made by the party of Mr. Bailey Willis. In this way 

the geologic observations on the present reconnaissance were made in 

the light of earlier work in adjacent parts of the Cascade Range.

GEOGRAPHY.

TOPOGRAPHY.

Primary divisions of the region. Between 119° 30' and 122° 45' the 

forty-ninth parallel crosses three distinct regions, viz, Okanogan 

Valley, Cascade Range, and the low coastal country west of the latter.

oGibbs, George, Physical geography of the northwestern boundary of the United States: Jour. 

Am. Geog. Soc., vol. 3,1870-1872, pp. 134-157; vol. 4,1372-73, pp. 298-392. Bauerman, H., Report on 

the geology of. the country near the forty-ninth parallel of latitude west of the Rocky Mountains, 

from observations made in 1859-1861: Ann. Rept. Geol. Survey Canada, 1882-1884.
BULLETIN NO.235 PL. I

U. S. GEOLOGICAL SURVEY

GathelrarPeak

JLoomis r^ I

Sandstone

and 

andesi

.v greenston

LINGHAM

i?

m e s t o n e

coal measures

Contours,interval 250feet Contours, interval 

based on. actual surveys 1000 feet,sketched

Roads IVails Routes followed 1901 International boundary 

offestablisnedtrails 4Sth.parallel

RECONNAISSANCE MAP OF THE CASCADE RANGE NEAR THE 49 PARALLEL

BY GEORGE OTIS SMITH AND PRANK C. CALKINS 

Scale

01234-56789 10 15 ?0 miles

TERTIARY MESOZOIC PALEOZOIC

0 123 4 5 6 7 8 9 10 15 20 kilometers Andesite Sandstone and Granite, grajiodiorite 

conglomerate anddiorite

Pasayten formation 

(lower Cretaceous)

*m-ti ttflTtti

Gabbro Pyroxeuite Slate,quartzit 

L_J 

e,ttchist,and Limestone; 

__beds and

anaperidotite greenstone (Carboniferous?) lenses in slate
TOPOGRAPHY. . 13 

OKANOGAN VALLEY.

Okanogan. Valley is the lowest point on the international boundary 

between Red River of the North and the Pacific coast. Lake Osoyoos 

has an elevation of 913 feet above the sea, so that the Okanogan has 

a deeper valley than the Columbia itself at the forty-ninth parallel. 

Within this valley there is considerable relief, the mountains south, 

of the big bend of Similkameeri River attaining an elevation, of 4,500 

feet. The topography is of the plateau type, \vith rounded tops and 

gentle slopes. The steep-sided canyons which cross the valley divide 

it into a labyrinth of channels, many of which are without drainage 

at present. These channels are largely the result of effective corrasion when the streams were swollen with the drainage of the melting 

glaciers. This whole valley, in fact, was occupied by a tongue of ice 

that came from the north and extended soutll across the Columbia.

For a few miles south of Lake Osoyoos the valley has a width of 

several miles and is floored with alluvium. Similar alluvial plains 

border Similkaineen River where it crosses the boundary and also the 

tributary stream by which Haipwil, or Palmer, Lake empties into the 

Siniilkameen. Extensive gravel terraces border both Okanogan and 

Similkaineen rivers as well as many of the dry channels.

CASCADE KANGE. 

GENERAL, CHARACTERISTICS.

The western limit of Okanogan Valley is very sharply defined at 

the boundary, this abrupt change in topography being due to the fact 

that the east side of the Cascade Range is there without the usual 

foothills. Mount Chopaka rises from the marshes bordering the 

Similkaineen as a steep wall over 7,000 feet in height. Standing on 

its summit one sees extending to the south and west a vast expanse 

of mountain peaks, with the white dome of Mount Baker in the far 

distance. These mountains, for the most part snow-capped in early 

summer, are the Cascades, which in this latitude have their maximum 

development, the distance from Chopaka to Baker being over 90 miles.

Northern termination of Cascade Range. A noteworthy feature of 

this region is the manner in Avhich this range loses its mountainous 

character immediately north of the forty-ninth parallel and descends 

to a plateau several thousand feet lower. PL IV, A, illustrates this 

abrupt change near the boundary, the view being to the north from 

a peak about 8,000 feet iu height on Bauerman Ridge. This feature is noticeable for essentially the whole length, of this section, 

and was noted by Gibbs/' who described the mountains east of the 

headwaters of the Skagit as having a uniform height, with few prominent peaks, and a general elevation of 5,500 to 6,000 feet, and noted 

that this equality of elevation does not exist south of the boundary.

«0p. cit., p. 350.
14 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [HULL.235.

The Avestern portion of this boundary section was rather thoroughly 

studied by Doctor Daly, of the Canadian survey, who calls attention 

to this same change in the topographic character of the international 

boundary. 0 "By a curious accident the international boundary line, 

roughly speaking, divides the coast range into two parts of contrasted scenic quality. In Washington the summits are the higher 

and more peaked, the ridges the more serrate, while all are dominated by the majestic cone of Mount Baker. On the Canadian side the 

massifs are somewhat lower, are more rounded, and less abundantly 

supplied with a perenriial snow cover."

In view of these observations it seems proper to consider the Cascade 

Range as finding its northern termination approximately at the for'tyninth parallel.

Subdivision of Cascade Range. In northern Washington, where the 

Cascade Mountains are so prominently developed, the range is apparently a complex one and should be subdivided. This was recognized 

by Gibbs, AV!IO described the range as forking and the main portion 

or "true Cascades" crossing the Skagit, where that river turns west, 

while the "eastern Cascades" lie to the east. Bauerman, geologist 

to the British commission, recognized three divisions, and as his subdivision is evidently based upon the general features of the relief it 

will be adopted here. To the eastern portion of the Cascades, extending from Mount Chopaka to the valley of Pasayten River, the name 

of Okanogan Mountains is given, following Bauerman. To the middle 

portion, including the main divide between the Pasayten, which 

belongs to the Columbia drainage, aud the Skagit, which flows into 

Puget Sound, Bauerman. gave the name Hozomeen Range, taken from 

the high peak near the boundary. For the western division the name 

Skagit Mountains is proposed, from the river which drains a large 

portion of this mountain mass and also cuts across its southern 

continuation. It will be noted that the north-south valleys of the

Pasayten and the Skagit form the division lines between these three 

subranges, which farther south coalesce someAvhat so as to make 

subdiAdsion less necessary.

OKANOGAN MOUNTAINS.

The Okanogan Mountains form the divide betAveen the streams 

.flowing north into the Siuiilkameen and thence into the Okanogan and 

those flowing south into the Methow drainage. In detail this divide is 

exceedingly irregular, but the range has a general northeast-southwest 

trend, joining the main divide of the Cascades in the vicinity of Barron. The highest peaks, such as Chopaka, Cathedral, Remmel, and 

Bighorn, haA^e a nearly uniform elevation of 8,000 to 8,500 feet, and 

commonly are extremely rugged. Over the larger portion of this 

area the heights are above 7,000 feet, and below this are the deeply

a Summary Eeport'Geol. Survey Canada, 1901, p. 41.
I HOZOMEEN RANGE. 15

cut valleys. A few small, glaciers exist on the northern sides of certain peaks at the head of some branches of the Pasayten, and the 

former extent and importance of glaciers in this region are shown, by 

the conformation of nearly every ridge and mountain in the range. 

As a rule, the south slope of every spur or ridge is regular and without marked features, while the opposite face is deeply carved with 

steep-sided cirques and gulches. Tiny lakes with bordering snow 

banks occupy almost all of these amphitheaters, in which head the 

streams flowing north into the Similkameen drainage system. In 

some cases the divides are cut well down, and the U-shaped, gaps or 

passes are occupied by grassy meadows. The tops or uplands in this 

area are generally only sparsely timbered, but bunch grass is abundant where the snow does not remain too long into the summer. 

The valleys are U-shaped, with moderate grade .and gravel-covered 

'bottoms and terraces along the lower courses of the larger streams. 

The tributary streams have steeper grades, but the bottoms nevertheless are often very marshy. In the valleys the timber, though 

small, is dense, and windfall areas are frequently encountered on the 

northern slopes.

HOZOMEEN RANGE.

The valley of the Pasayten, which heads 20 miles south of the 

boundary, has an elevation of 3,500 to 4,500 feet in the main portion, 

and is a broad feature well adapted to serve as a natural boundary 

between the Okanogan Mountains and the Hozomeen Range. This 

latter range includes the main crest of the Cascade Mountains and 

takes its name from Mount Hozomeen, a prominent peak close to the 

forty-ninth parallel and overlooking Skagit River. The valleys of 

Pasayten and Skagit rivers are nearly parallel and only about 20 miles 

distant, so that the tributary streams flowing east and west from the 

crest have a very rapid descent and flow in canyons which deeply dissect this rugged range. In the western part of this range the creeks 

entering Skagit Valley have remarkably narrow canyons, which at 

their mouths are barely wide enough for the passage of the stream. 

Above, the valleys widen somewhat and apparently have much lower 

grades in some parts of their courses. Devil Creek, for instance, 

enters Skagit Valley through a cleft in the rock wall, yet this tributary extends about 8 miles back and drains a wide basin.

The divide has an elevation of from 7,000 to 8,000 feet, and about' 

10 miles south of the boundary is made up of sharp peaks which owe 

their rugged outlines to the beds of coarse conglomerate of which 

they are composed. The spurs in this central portion of the Hozomeen Range are rather level topped, and north of the boundary the 

topography becomes much less bold in character. The western, portion of this range has even higher and sharper peaks, of which Mount 

Hozomeen is the type. Being close to Skagit Valley, which here has 

.an elevation of from 1,400 to 1,700 feet, and isolated by the deep
16 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BULL.225.

gorges of the tributary streams, these mountains, some of which, 

notably Mount Hozorneen and Jacks Mountain, probably reach an 

elevation of 9,000 feet, command attention from whatever side they 

are seen. Numerous glaciers are found in this region, and glacial 

cirques have been cut back into the mountain masses until the peaks 

are of the Matterhorn type.

SKAGIT MOUNTAINS.

The upper valley of the Skagit extends southward from the iortyninth parallel as a broad A^alley with gravel-covere'd bottom and low 

grade. The river in this portion of its course has many meanders, 

and swamps occupy large areas in its AT alley. Large timber is found 

here, and the dense undergrowth of the west slope of the Cascades 

makes its appearance. Below the- point where Beaver and Ruby 

creeks enter the Skagit the river turns west, and in a wild canyon 

cuts through the mountains. The spur of the Cascades, which is 

crossed by the Skagit at this point, extends northwest, and is the 

range to which the name of Skagit Mountains is here given.

Without question the Skagit Mountains, which form the western 

subrange, include the wildest and most rugged country in the whole 

Cascade Range. Looking west from the valley of Skagit River one 

sees high peaks with precipitous faces, on whose lower slopes are 

extensive glaciers, from which flow Beaver and Glacier, or Little 

Beaver, creeks; and the scene is no less picturesque when viewed from 

the west in the vicinity of Hannegan Pass. For this mountain mass, 

which extends south from the boundary, the name of Ouster Ridge 

is proposed, in honor of Mr. H. Ouster, who had charge of the reconnaissance party of the United States Boundary Survey that in 1S59 

crossed this ridge from the headwaters of the Chilliwhack, making its 

way down Glacier Creek to the Skagit, a trip probably not duplicated 

by any explorer, despite some unsuccessful attempts. Mount Shuksan, farther west, is another example of the sharp pyramidal peaks 

characteristic of this region about the headwaters of Nooksak and 

Chilliwhack rivers'. So many of the mountain slopes are precipitous 

that much of the country is practically inaccessible and unknown 

even to the prospectors.

Another extremely rugged part of the Skagit Mountains lies on the 

.forty-ninth parallel, between Silicia (or Slesse) and Tummeahai creeks. 

Smallglaciers flank the higher peaks and represent the larger glaciers 

that have been so efficient in the development of the present topography. One feature well exhibited at the head of Tummeahai Creek, 

and common elsewhere in this region, is the occurrence of a succession of amphitheaters similar to those to which Daly has applied the 

expressive term "tandem cirques." This type of sculpture is plainly 

the result of glacial work. The stream gradient that is found in such 

a valley is an alternation of rapid cascade and flat reach, the latter
I DRAINAGE' AND OLTMATE. 17

often widening into a small lake or a mountain meadow through which 

the stream meanders. The valley walls are very steep, and slopes of 

80° to .85° are not uncommon. From one point of view at least ten 

such cliffs could be seen.

Farther west the Skagit Mountains are somewhat lower, and serrate 

ridges and pinnacles, like Mount Shuksan, are succeeded by broader 

ridges, essentially flat crested, smooth, and grass covered, separated 

by the deep canyons of the Nooksak and its tributaries. The canyons 

are rather broad and have gentle grades, so that it is only the luxuriant vegetation that prevents easy access to this portion of the range, 

which includes the Mount Baker mining district. The glacier-covered 

cone of Mount Baker is prominent, rising nearly 5,000 feet above the 

high plateau that forms its base, and standing somewhat apart from 

the high peaks of the Skagit Mountains.

The east limit of the Cascade Range is at about longitude 120°, 

Avhere there is an abrupt descent to the gravel-covered plain that 

extends west to Semiahmoo Bay. Siimas Prairie is probably less than 

50 feet above sea level, and from its eastern border precipitous walls 

of rock rise almost a thousand feet, making a most noticeable topographic feature. To the west the plain is somewhat diversified with 

low ridges and hills, but this relief.is comparatively inconspicuous.

DRAINAGE.

Almost the whole of the region included in. this boundary section is 

drained by the three rivers, the Similkameen,. the Skagit, and the 

Nooksak. Small headwater streams tributary to the Methow and the 

Frazer drain the remainder. Similkameen River, where it crosses 

the boundary, is deep and swift. Its tributaries, the Aslmola and 

the Pasayten, which are encountered farther west in the Okanogan 

Mountains, have steep gradients, but -can be easily forded. Skagit 

River at the forty-ninth parallel has a considerable volume of water 

and is deep and rather sluggish, but 30 miles below, where it enters 

its canyon, it is an impetuous river, with few quiet places along its 

course. The tributaries of the upper Skagit from both the east and 

west are short streams with steep grades and many cascades. The 

North Nooksak occupies a valley with somewhat even grade, except 

at one point where the channel narrows and the river dashes over the 

Nooksak Falls, which are nearly 100 feet high.

Small glaciers persist in the Okanogan Mountains, notably on Jacks 

Mountain in the Hozomeen Range and in the Skagit Mountains on 

Ouster Ridge at the head of the North Nooksak, as well as on Mount 

Baker.

CLIMATE.

Within this 150-mile section along the forty-ninth parallel there is 

a considerable range in climatic conditions. In the vicinity "of Lake 

Bull. 235 04- 2
18 CASCADE EANGE NEAE FORTY-NINTH PAEALLEL. [ BULL. 235. .

Osoyoos the country has a decidedly desert aspect, cactus and sagebrush constituting the characteristic' vegetation and forming an index 

of the comparative aridity. Few trees are seen, and bunch grass is 

less abundant than it is either east or west of this low country. The 

occurrence of undrained alkali lakes in this vicinity also testifies to 

the small annual precipitation. The summers are hot and dry, and . 

the dry season is probably longer here than at any point on the northwest boundary west of the Great Plains region.

The Cascade Range, on the contrary, is a region of short summers. 

In the Okanogan Mountains the snowfall is not so heavy as farther 

west, but not until the middle of July does the snow disappear sufficiently to enable the region to be easily traversed. Several miles 

south of the forty-ninth parallel deep snow remains on these mountains throughout the summer, and snow squalls occur occasionally 

even in July and August. The summer months, however, are comparatively free from rains, and Avhile the nights are cold the area is 

one well adapted for camping expeditions. -

Similar climatic conditions obtain in the eastern part of the Hozorneen Range, but as soon as the western slope is reached evidences of 

the greater annual precipitation are at once noticed. The vegetation 

changes its character, the forests are more extensive, large trees with 

dense underbrush cover the valley bottoms and extend well up the 

slopes, and except on a few ridges grass is not plentiful. The banks 

of snow that persist throughout the year become more and more 

troublesome, and glaciers are seen on all the higher peaks. All of 

these features become even. more noticeable Avest of Skagit River inthe high country of the Skagit Mountains. Here the summer is A^ery 

short, and July and August are the only months in Avhich snow does 

nob fall in considerable amounts, and at no time in the year are the 

passes in the Skagit Mountains free from SHOAV. The low-hanging 

Clouds and frequent snOAVS in early September seriously embarrass

The climatic differences betAveen the east and west slopes of the 

Cascades are Avell shoAvn in the condition of the old vistas which were 

cut on portions of the boundary line. In the Ashnola and Pasayten 

valleys the old cuttings can be easily found, and the stumps and logs 

are sound. In the stations occupied OA^er forty years ago the hewn 

blocks upon Avhich instruments Avere placed and' the camp stools 

remain as - they were lef t, Avhile at the Ashnola monuments ladders 

used in the construction of the high rock cairns are still solid. On the 

Avestern slope, in Skagit Valley, the old stumps are so much decayed 

that only rarely can they be surely recognized as such, and the chopped 

surface must be hunted for on the ends of the logs. In the vista here 

and in the other localities farther Avest trees 75 feet high and 14 inches 

in diameter haA^e groAvn up in the old cuttings, Avhile dense underbrush 

most effectually conceals the line as once cut out.
SOAt,KiNS.D l BOADS AND TRAILS. ' 19

AVest of the Cascades, in the kny country extending to the coast, the 

climate is that characteristic of the Pugjst Sound region. The winters 

"are not severe, there being little or no snow, and the rainy season 

extending from October to June. The summers are warm, with little 

rainfall.

ROADS AND TRAILS.

Within Okanogan Valley there are good roads, from Avhich trails 

lead in every direction. A trail also extends Avest from the Loomis 

road to two ranches upon the south slope of Mount Chopaka, about 2 

miles west of Haipwil, or Palmer, Lake. Beyond this there is an old 

trail that can be followed for 7 miles. There is some marshy country 

here, and also bad windfalls, so that this trail is hardly passable for 

pack animals. Beyond this there is no established trail and only for 

a short distance are there any signs to indicate that the region is ever 

visited. In the six weeks spent in traversing the section-between 

Mount Chopaka and Barren no person was met by our party. The 

camps of the boundary survey of 1859 remain much as they were left. 

A few blazed lines in the Ashnola and the Pasayten valleys mark 

where trappers sometimes penetrate this country from the north, 

while along the latter valley there is an old trail leading from Princeton, in British Columbia, to Barron. This trail, however, has been 

little used in late years and near the boundary is much obstructed.

As can be seen on the map (PI. I), a practicable route for the pack 

train was found following close to the divide between the streams 

flowing northward into the Ashnola and the headwaters of Chiwak 

Creek. This route crosses Bauerman Ridge and keeps within two 

miles of the boundary as far as Cathedral Peak. Little cutting is 

necessary to work across this part of the region, although there are 

several areas of old burns where there are bad windfalls. The ridges 

are usually rugged, but close to the conspicuous Cathedral Peak 

(PI. Ill, J3) there is an easy pass to the more open country to the west. 

Here most of the ridges are broad and only scantily timbered, bunch 

grass growing abundantly. Thus the only obstacle to travel with 

pack animals is found in the more heavily wooded bottoms where the 

larger streams are crossed. The beautiful open character of the 

uplands is best seen at Park Pass, west of which the route followed 

in 1901 was more' south of wesb, and the only serious difficulty 

encountered was in crossing the deep valley in which the Hidden 

Lakes lie. The Pasayten Valley can be readied perhaps more easily 

by following the ridge which extends west from Park Pass, and the 

greater part of this distance, in .fact, was traversed on horseback in the 

course of the reconnaissance.

The route followed, up Pasayten Valley to Windy Pass, and thence 

down past Barron on Slate and Ruby creeks to the Skagit River, was 

on old trails of varying quality. No trails cross the Hozoineen Range
20 CASCADE EANGE WEAK FORTY-NINTH PARALLEL. [BULL.235.

north of Ruby Creek, although these mountains could be penetrated 

with horses both from the Pasayten Valley and up Canyon Creek. 

The Fort Hope trail up the east side of Skagit River has been abandoned for many years, except for a few miles at the lower end. Two 

prospectors traveled this trail with horses in 1901, but it is so badly 

blocked with fallen timber as to be difficult to follow on foot, and 

along the river bank the underbrush has so completely hidden the 

trail that for hundreds of yards it can be followed only by the feet 

feeling out the worn rut. At the time of the rush to the Ruby Creek 

placers, in the early seventies, this was the-route by which the region 

was entered, and the trail was undoubtedly in excellent condition.

The Skagio Mountains are accessible only from the north and west. 

The Canadian boundary party in 1901 opened up trails along most of 

the streams tributary to the Chilliwhack as far as the forty-ninth 

parallel. From the west the state wagon road extends from Maple : 

Falls along the North Nooksak to Shuksan, from which trails extend 

north across Twin Lake Pass to the Lone Jack mine, west up the 

river to Haimegan Pass, and south to the divide at the head of Baker 

River.

In brief, it may be stated that in the eastern portion of the section the absence of trails does not seriously trouble anyone wishing 

to traA^erse the region, but on the Avestern side of the main divide the 

dense A'-egetation and the extremely rugged topography make it necessary to folloAv Avell-established trails, and the construction of IICAV 

trails involves considerable expenditure of time and money.

GEO:LOGY.

DESCRIPTION OF FORMATIONS.

CLASSIFICATION AND MODE OF TREATMENT.

It Avi.ll be useful to introduce the discussion of the geology of the 

region by a brief statement of its plan and scope. It has been the 

endeavor to make these harmonize 'with the character of the field work 

upon Avhich the report is based. A hurried reconnaissance through 

territory comparatively HCAV to geologic exploration can not serve as 

the basis of complete and detailed description nor of exa'ct correlations. The descriptions Avill therefore be made, brief and general, 

and correlations, especially in the case of the older rocks, will generally be somewhat broad and in many cases merely tentatiA^e.

The stratified rocks, including some schists of uncertain origin, and 

the contemporaneous A^olcanics interbedded Avith the sedimentary 

deposits Avill be treated first, deferring the consideration of the important intrusive masses to the last. The primary grouping of these 

stratified rocks is based on geologic age, the divisions being made 

sufficiently broad to avoid committing the authors to any correlations 

more definite than their knowledge appears to Avarrant. The further
PRE-CRETACEOUS BOCKS. \ 21

subdivision of the groups thus blocked out is chiefly geographic, and 

the rocks belonging to each of the primary divisions are described for 

each district in which they are represented.

The plutonic masses and the dikes associated with them are treated 

separately from the stratified rocks for two reasons. In the first 

place, their ages are in general still less definitely known, and in the second place their petrographic relations to one another are more clearly 

brought out by placing them together.

In this section the igneous rocks will be made the subject only of 

such description as will be interesting and comprehensible to the 

reader unskilled in technical petrography. The various types will be 

defined rather broadly according to characters recognizable in the 

field. Their areal distribution will be described and their geologic 

relations pointed out in so far as they have been determined. For 

the benefit of petrographers the more exact descriptive data obtained 

by microscopic study and the discussion of certain petrologic questions will be incorporated in another chapter.

PKte-CKETACEOUS KOCKS. 

GENERAL CHARACTER AND DISTRIBUTION.

Along the route of the party were found many important bodies of 

rocks, for the most part greatly metamorphosed, which appeared to 

be undoubtedly pre-Cretaceous. In the case of many of these a much 

more definite geologic age could be assigned with a fair degree of 

confidence, but in the- case of many others, probably belonging to 

widely different periods, the existing evidence is insufficient to form 

a basis for any but broadly .general and tentative statements a fact 

that seems to render impracticable the application of any general 

subdivision of these.old .rocks throughout the region. For purposes 

of description, therefore, the strata in question are grouped together 

as pre-Cretaceous.

The rocks considered to be pre-Cretaceous include (1) some very 

old-looking schistose rocks along Columbia River and lower Okanogan 

Valley, (2) an assemblage of supposedly Carboniferous sedimentary 

and volcanic rocks exposed' in the more northern part of Okanogan 

Valley, (3) strata somewhat similar to those last mentioned exposed 

 in the basin of upper Skagit River, (4) some old sediments and a great 

volcanic mass seen in the vicinity of Hamilton, and (5) a great assemblage of strata ranging from Paleozoic to Jurassic to the west and 

north of Mount Baker. The rocks of each of these areas will'be 

described and the available evidence will be given in regard to their 

stratigraphic sequence and geologic age.

COLUMBIA AND LOWER OKANOGAN VALLEYS.

Immediately above the Wenatchee basin, which is carved in soft 

Tertiary sandstones, the Columbia flows in a gorge intrenched in excep-
22 CASCADE RANGE NEAR FORTV-NINTH PARALLEL. [ButL.235.

tionally. resistant schistose rock. Immediately north of Wenatchee 

River a granitoid gneiss crops out, which appears to grade into the 

thinly laminated rock, of schistose rather than gneissic characterj 

that forms the walls of the canyon farther north. In addition to the 

schistosity which causes weathered fragments to separate readily into 

thin slabs, there are several systems of joints, four well-marked joint 

planes being observed, for example,.at one spot. While no microscopic examination of this rock was made, observations in the field 

showed that it consisted essentially of quartz and feldspar, with both 

light and dark mica.

Schists of similar character were the principal country rocks along 

the route traversed from a point near the mouth of Knapp Coulee to 

Chelan Falls. Still another mass of schist, or fine-grained gneiss, 

was observed to form a portion of the walls of Antoine Coulee near 

its north end.

In the vicinity of Clover light-colored schists or gneisses occur, 

similar, in a measure, to those of the Columbia gorge. The prevailing 

type found was a light-gray medium-grained laminated rock, which 

may be seen megascopically to consist essentially of feldspar, quartz, 

and biotite. At the same locality there were seen in small quantity 

darker biotitic schists and light gray-green pyroxene schists, probably 

produced by contact metamorphism from impure limestones.

Mention should also be made here of a mass of gneiss from which 

is carved a glaciated ridge north of Riverside, separating the main 

valley from a high abandoned side channel. The rock is a gray, wellfoliated augen-gneiss, probably derived from a porphyritic granite. 

No specimens were collected to serve as a basis for detailed description.

UPPER OKANOGAN VALLEY.

In Okanogan Valley, from the vicinity of Riverside to the boundary, old rocks that have undergone considerable metamorphism are 

abundantly developed. On lithologic grounds they are tentatively 

classed together and correlated with the Cache Creek series of Dawsou,'1 which is of Carboniferous age. It was in the vicinity of Oroville and Loomis that the rocks were most thoroughly studied, and it 

seems to be there also that the series is most typically developed.

The supposed Cache Creek series, as represented in this district, 

comprises both sedimentary and volcanic rocks. Its lower portion 

consists chiefly of clay slates and graywacke slates, usually of gray 

or greenish color, together with some moderately coarse metamorphic 

sandstones and fine conglomerates, but comprises no coarse conglomerates. Occasionally the arenaceous portions of the series take on 

 the character of fairly pure quartzite. Material of this sort becomes 

especially abundant near Mount Chopaka. In the upper portion of 

the series, as developed at Loomis, there are at least two beds of lightf'Ann. Kept. Geol. Survey Canada, new ser., vol. 7,1894, pp. 37B-49B.
SOALKIMS.D ] PRE-ORETACEOU8 BOCKS. 23

gray limestone, whose areal distribution is indicated roughly on the 

geologic map. Farther south, to the west and northwest of Riverside, this rock plays a more important role. The western wall of the 

coulee north of that place is a cliff perhaps 200 or 300 feet high and 

composed mainly of limestone.

The upper part of the series comprises large volumes of volcanic 

material, which it was not found practicable to separate, on the preliminary map, from the slaty rocks. These old volcanics are for the 

most part extensively developed on the southern end of Palmer 

Mountain, in the basin southeast of that point, to the west of Blue 

Lake, and on the hill southwest of Palmer Lake. Lithologically, they 

were roughly classified in the field as greenstones. In broad, distant 

views the dark brownish hues of the weathered surfaces and their 

rugged erosion forms give them a resemblance to basaltic rocks. In 

hand specimens their original character is found to be obscured by 

decomposition, but the porphyritic texture is occasionally noted, as 

well as amygdaloidal structure and brecciated structure suggestive of 

pyroclastic origin. Microscopic study of these rocks is productive of 

no very satisfactoiy results, owing to the advanced decomposition 

which they have universally suffered, the original materials being 

almost always completely replaced. The character of the resulting 

secondary minerals, however, as well as the textural features, confirms 

the field diagnosis of the rocks. They are basic extrusives, probably 

for the most part basaltic, though perhaps including some basic 

andesite. Pyroclastics appear to be fully as abundant as the massive 

lavas.

The rocks tentatively referred to the Cache Creek series have suffered various degrees of metamorphism. The sedimentary portions 

have in general an indurated slaty character in the localities removed 

from granitic intrusions. In the vicinity of the several intrusive 

granite contacts, however, much more advanced alteration has taken 

place, the slates being more or less completely converted to micaschist. Interesting changes have been produced also in the basic eruptives by the granitic intrusions, file description of which will be 

deferred to the chapter on petrography.

BASIN OF UPPER SKAGTT RIVER. *

The upper part of Jacks Mountain, or Mount Nokomokeen, is 

carved from a series which has the aspect of being much older than 

the Cretaceous rocks farther east and may be equivalent to the supposed Cache Creek of Okanogan Valley. It comprises both sedimentary and volcanic rocks.

Most prominent of the sedimentaries are quartzites and bedded 

cherts. The latter are generally of a light-gray or drab tint and are 

cut by innumerable veinlets of quartz. Their bedding is their most 

noteworthy feature. They are built up of distinct laminse, about an
24 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BULL.235.

inch in average thickness, readily separable from one another. The 

.similarity of their structure with that of the red chert's of the Franciscan series in California is striking. As in the supposed Carboniferous of Okanogan Valley, there are beds of limestone (which are, 

however, rather thin and lenticular), and the highest portion of the 

mountain reached was built up largely of altered volcanic rock, 

among which amygdaloids were observed. Although obscured greatly 

by alteration, the constitution and texture of these rocks as observed 

under the microscope indicate that these old lavas are basaltic.

The lower portion of the mountain, is composed in part of dark 

mica-schists cut by dikes; that often show considerable shearing, and 

may be contemporaneous with the foliated granodiorito of the valley 

below. The mica-schists are completely metamorphosed, and impress 

one as being much older than the rocks already described as forming 

the upper portion of the mountain.

Old schists, slates, cherts, and quartzites are also the principal 

country rocks in the valley of .the Skagit above Ruby Creek, as far 

north as Jackass Point, but some "greenstone " (basalt or basic andesite) also occurs. North of Jackass Point the country rock is mainly 

granitic, though interrupted by a belt of slate. The impression of the 

observer was that these sedimentary arid volcanic rocks were plainly 

older than the Cretaceous and might in part be correlative with the 

Cache Creek series. . .

LOWER SKAGIT VALLEY.

From Marbleinount to Hamilton the sides of Skagit Valley are chiefly 

made up of old rocks. In 1898 Messrs. Willis and Smith made a reconnaissance of a portion of the Northern Cascades, including Skagit 

Valley from Sank to-Hamilton, and since the authors passed through 

this region rapidly in 1901 without making any new observations of 

importance a brief outline of the facts observed in.the earlier reconnaissance may be presented here. . At three localities in the valley of the Skagit sedimentary rocks 

were observed. On the southwest side of Sank Mountain there are 

calcareous grit and slate, marble, and slate containing iron carbonate. 

A little wrest of Sank, limestone, black slates, and sericitic slates 

occur, the phyllites forming the walls of Phinney Creek Canyon. 'The 

canyon of Baker River near its mouth is carved in limestone, cherty 

grit, and black slate. In the limestone occur some crinoid sterns, which 

are the only fossils that have been found in the old rocks of this district, but they give practically no evidence in regard to the age of the 

rocks.

" South of the Skagit, from Sank River west to near the longitude of 

Hamilton, there is exposed a rock series distinctly more metamorphosed than the old rocks to the north and presumably of greater age. 

The rocks of this area comprise black and green slates, crystalline
SCALKTNS.D ] PRE-CRETACEOUS ROCKS. 25

schists, chiefly chloritic and glaucophanitic, with ferruginous qnartzites and jaspers. These quartzites are colored by oxides of iron, 

including both magnetite and hematite. They are sometimes banded 

parallel to the bedding and sometimes brecciated, in which latter case 

the angular reddish fragments are cemented by purer quartz.

One of the beds in the old series is so rich in iron as to have attracted 

the notice of prospectors. This ore band is definite and quite extensive, and shows a banding parallel to that of the schists with which it 

is associated. In cross section it shows a gradation from a pyritiferous slaty margin to more concentrated ore, richer in magnetite in the 

center. The thickness of the ore body at the Birds view prospect is 

only about 3 feet, and it has not proved sufficiently rich, in view of 

its small volume, to lead to exploitation.

In addition to the old inetaniorphic rocks already described, there 

is also in. this region an old volcanic series that is probably.younger. 

These ancient volcanics were observed along the route of 1901 between 

Marbleinount and Sank. They also form Sank Mountain, where their 

field characters were observed by the senior author in 1895. The rugged 

crest line of that elevation illustrates the characteristic erosion forms 

of the material. .

In the field the volcanic nature of the rocks is easily recognizable, 

and their extrusive nature is proved abundantly by the frequent 

occurrence of amygdaloidal and pyroclastic structures. Their prevailing color is dark green, indicating their basic composition. Studied 

microscopically, they prove to be altered pyroxene andesite, a rock 

very common in the Cascades, where it has been, erupted at various 

geologic periods.

MOUNT BAKER DISTRICT.

Preliminary statement. The sojourn in the northwestern part of the 

boundary region was shortened by the approach of winter, and observations were confined almost entirely to traverses along the principal 

roads and trails. The description of the older rocks of this district 

can therefore be only of the most general character, and few statements can be made in regard to their age, which probably ranges from 

early Paleozoic to Jurassic, or possibly as late as Cretaceous.

Dr. R. A. Daly, of the geological survey of Canada, made, in 1901, 

a survey of the country just north of the boundary from the coas't to 

Chilliwhack Lake, much more detailed in character than the reconnaissance of the present authors. He has found Paleozoic fossils in a 

series of shales and limestones which may be the equivalent of some 

of the old rocks exposed at Bear Mountain and about Twin Lakes.

The bedded rocks of the region may be divided roughly, for purposes of description, into three groups, as follows: (1) Metamorphosed, 

chiefly sedimentary, rocks, probably Paleozoic; (2) sedimentary rocks, 

generally not much metamorphosed, probably Mesozoic; (3) an area 

of volcanic rock of indeterminate age near Hannegan Pass.
26 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BULL.235.

Supposed Paleozoic rocks. The rocks assigned to the first group 

were' observed north of Hardan or Maple Falls, and in the eastern 

portion of the district, where they are the country rocks of the most 

important mines. Rocks that should be grouped with these also 

occur along the Seattle and International Railway south of its crossing 

of South Fork of the Nooksak. and on the highlands between Middle 

Fork and North Fork.- In this western area the old rocks are schists, 

slates, and quartzites, with perhaps some altered volcanic -materials. 

The beds appear to have suffered intense folding, and no structure 

could be definitely made out in the hasty examination. O

The rocks of the eastern area were somewhat more thoroughly 

examined. At Twin Lakes Pass there are metamorphosed sandstones 

and slaty rocks with peculiar breccias and conglomerates of limestone 

fragments in a slaty matrix. Along Tummeahai Lake the rocks of 

the supposed Paleozoic are less altered and deformed, but characteristic breccias of calcareous slate occur which resemble the limestone 

breccia near Twin Lakes. Some volcanic breccias occur here, apparently interbedded with the sedimentary rocks. Along Swamp Creek 

trail also the country rocks appear to belong to the old group and 

comprise sandstones, slates, and shales, with considerable volcanic 

material. These old volcanics are much altered, but microscopic 

study shows that although they include some rhyolite and dacite they 

are mainly andesitic lavas and tuffs.

East of Twin Lakes and in the canyon of Ruth Creek the rocks of 

this older group are more thoroughly metamorphosed, a fact probably 

due to their invasion by the large mass of granite from which Mount 

Shuksan and the ridges north of Hannegan Pass are carved. Their 

irruptive relation to the slaty rocks was clearly seen at Mamie Pass.

The most abundant rock'in this metamorphic area might be called 

a gneiss rather than a schist, but is plainly of sedimentary origin. In 

mass it shows a blue-gray tint, but in the hand specimen shows a 

characteristic ^vavy lamination, marked by the alternation of light 

and dark layers a.few millimeters in thickness. The dark layers are 

blue gray and slaty looking, and probably contain carbonaceous material, while the light layers are almost pure quartz. The quartz layers 

are not continuous, but have the character of thin deformed lenses, a 

feature that suggests that they may be of the nature of gash veins. 

Gash veins whose dimensions are to be expressed in inches occur 

abundantly, and frequently carry sulphides. It is in this type of 

rock that the Lone Jack vein is located.

Another schist found near Lone Jack mine suggests by its general 

appearance and mineralogic character a derivation from some basic 

volcanic rock. The old metamorphics of the Mount Baker district 

are often intensely crumpled and are generally cut by joint planes.

The schists exposed along the route from Sedro-to Acme are, in the 

main, of a somewhat slaty or phyllitic character, with thin and often
PBE-CEETACEOUS BOOKS. 27

extremely crumpled laminae. In color, they are prevailingly bluish. 

They have " gash veins " of quartz parallel to the lamination, but 

these are much less numerous than in the schists of the Silicia Creek 

district, to which they seem to be very similar, though less thoroughly 

metamorphosed.

In the vicinity of Wickersham there is apparently in this blue schist 

series a rock which, though with well-developed cleavage and jointing, exhibits distinctly a moderately coarse clastic structure, being 

composed of fragments of various tints of gray about 2 millimeters in 

a vera'ge diameter. All these fragments have been thoroughly squeezed, 

so as to have a slaty structure, and are, as it were, so welded together 

that the rock splits across them indifferently.

Near the intersection of the western boundary of the Washington 

Forest Reserve with the parallel 48° 50' N., gray, slaty, and phyllitic 

rocks, highly crumpled, and evidently very much older than the Tertiary sandstones by which they are overlain, are exposed. They are 

not improbably connected with the rocks of the last area described.

Supposed Mesozoic rocks. For some miles below Shuksan the outcrops on the walls of the canyon of the North Nooksak are of sedimentary rocks distinctly less metamorphosed than those assigned to 

the Paleozoic. They are mainly sandstones, with.some cherty layers 

and conglomerates. Green colors are rather characteristic of all the 

rocks. At Austin Pass there are greenish sandstones and banded 

shales which show on the average about the same degree of indura: 

tion as the similar rocks of the Pasayten formation. On lithologic 

grounds, then, it appears probable that there may be a belt of Mesozoic 

rocks trending northwest from Austin Pass.

There is, moreover, some paleontologic evidence bearing on this 

question. In 1898 there were sent to Mr. J. S. Diller by Mr. W. H. 

Fuller, of Fairhaven, Wash., some fossils collected on Cowap, or 

Canyon, Creek and on the ridge north of it. Mr. T. W. Stanton 

examined the material and reported on it as follows:

The .* * * fossils * * * are evidently all from one horizon, which I 

believe to be tipper Jurassic, this opinion being based chiefly on the distinctly 

striated form of Aucella, identified with A. erringtoni (Gabb) of the California 

tipper Jurassic Mariposa beds. This species was collected at both localities. The 

collection from Canyon Creek includes also a fragmentary Pleuromya and the 

impression of a small belemnite.

The collection from the divide between Canyon Creek and the waters of Fraser 

River contains the Aucella erringtoni, a fragment of an ammonite apparently 

belonging to the genus Steplianoce.ras, a small slender belemnite like that from 

the last-mentioned locality, and the phragmacone of a large robust belemnite.

Volcanics near Hannegan Pass. North of Hannegan Pass the 

granite is overlain by volcanic rocks, in part massive, but chiefly consisting of green and purple breccias apparently of andesitic character. 

Dikes apparently connecting with these extrusives cut the granite, and 

further evidence of their relation to the older rocks is found in the
28 CASCADE EANGKE NEAR FORTY-NINTH PARALLEL. [BULL. 235.

presence of fragments of granite and schist in the breccias. These 

are probably the rocks through which the'vents penetrated, indicating that the eruption was local in its character. Regarding the period 

of this eruption, it can only be said that the appearance of the rocks 

indicates that they are much older than the lavas of Mount Baker, 

while the other limit to their age is given by their relation to the 

granite.

CRETACEOUS STRATA.

PASAYTKN FORMATION.

Occurrence. Professor Russell, in his reconnaissance of 1901, 

examined an assemblage of folded sedimentary strata in the neighborhood of Barren and Crater Pass/' From these rocks he collected 

fossils which are commented on in the following extract from his 

report:

A thick bed of bluish sandstone at the base of -Gold Ridge, penetrated by the 

tunnels of the St. Paul and Minneapolis mines, contains fossil fern and nearly 

upright tree trunks. One sample of fern collected has been determined by F. H. 

Knowlton as approaching closely Dryopteris oerstedi, from the Cretaceous rocks of 

Greenland. A siliceous limestone in the same ridge, but several hundred feet 

higher in the series and extending southward to the border of Crater Pass, is 

abundantly charged with bivalve shells, which, as determined by T. W. Stanton, 

 are of a species of Actceonella. The evidence furnished by the fossils just mentioned indicates a Cretaceous age.

The authors of this paper found that these Cretaceous beds extended 

eastward along their route to the Hidden Lakes and were very extensively developed to the north, and believe that they extend west to a 

point not far above the mouth of Granite Creek. In this, however, 

they differ from Professor Russell, who believes that the slaty'rocks 

with steep dips exposed along lower Slate Creek and Ruby Creek are 

much older than the Cretaceous. 6 .This opinion, however, is not supported by stratigraphic evidence, but apparently rests merely on the 

older appearance of the rocks to the west, due to greater metamorphism. 

The value of this lithologic evidence will be considered presently; 

meanwhile it may be said that, the authors do not consider that the 

assumption of the pre-Cretaceous age of these beds is justified, and 

have provisionally considered them as belonging in the same formation with those at Barron.

Name. To the rocks of this locality which he recognized as Cretaceous Professor Russell provisionally applied the name Similkameen'formation/ This name was, however, applied ten years earlier 

by Dawson to a Miocene formation in British Columbia,* and hence* it

"Russell, I. C., Geology of Cascade Mountains: Twentieth Ann. Rept. U. S. Geol. Survey, pt. 2, 

1900, pp. 114-117. . . 

&0p. cit.,p. 112.

cOp. cit., pp. 114-117. _ 

i, J. W., Proo. and Trans. Royal Soc. Canada, vol. 8, sec. 4,1800, pp. 75-91.
U, S. GEOLOGICAL SURVEY BULLETIN NO. 235 PL.

A TERTIARY SEDIMENTS, SQUANTL FALLS, SIMILKAMEEN RIVER, WASHINGTON,

B. CRETACEOUS CONGLOMERATE FORMING CREST OF HOZOMEEN RANGE, 

Head of Three Fools Creek, Washington.
PASAYTEN FORMATION. 29

*

seems advisable to abandon it. As a substitute,, the name Pasayten 

formation is proposed. This name, rather than Sim ilkameen, is appl ied 

on all of the old as well as the most authoritative of the more recent 

maps to the stream which is the southwest tributary of the main 

Sim ilkameen, so that it is also on this account more appropriate as a 

formation name for the rocks here described.

Lif.hotoyic character and thickness. The Pasayten formation is composed of sedimentary rocks without contemporaneous volcanic materials. East of the main fork of Pasayten River sandstone appears to 

be the dominant rock. It is along the main divide north of Barren 

that the most instructive exposures of the Pasayten formation are seen. 

The lowest part of the section, as seen along the crest of the Ho/omeen 

Range, includes at least 1,000 feet of black shale. Above this shale 

is a sandy conglomerate, with pebbles from 1 to 8 inches in diameter. 

About 500 feet of this conglomerate io exposed at the head of Canyon 

Creek. Sandstone overlies the conglomerate and is succeeded by more 

black shale. The steep dips here indicate the presence of a "great 

thickness of these rocks, which extend far out on the spurs at the 

head of Three Fools Creek (PI. II, J5), so that 6,000 feet would appear 

to be a very conservative estimate for the thickness of the Pasayten 

formation.

There are a few thin and discontinuous beds of limestone in the 

Pasayten formation, but they constitute only an insignificant proportion of its. total volume. Along the lower portion of Slate Creek the 

supposed Cretaceous rocks are mainly black indurated shales with 

nearly A^ertical dips.

The argillaceous portions of tlie Pasayten formation are generally 

dark-colored, distinctly bedded shales. They are often siliceous and 

in general more or less indurated, and are popularly referred to as 

"slate." In no case, however, was there observed any true slaty 

cleavage oblique to the bedding. The beds upon lower Slate Creek 

and Ruby have, as their high dips indicate, suffered more intense 

folding than those to the east, and are in general more indurated. 

There is, however, no difference between these rocks and the shales 

of known Cretaceous age such as would justify their separation on 

lithologic grounds.

The sandstones, while occasionally quart/itic, are more commonly 

 gray or greenish gray in color, and evidently composed in large part 

of feldspar and rock fragments. The conglomerates contain a variety 

of pebbles, including several granitoid rocks, gabbro, diabase, metamorphosed volcanics, chert, quartette, and vein quartz, illustrating 

the character of the pre-Cretaceous formations of the region.

The whole series has undergone a considerable degree of " static " 

metamorphisrn, as shown by the generally thorough cementation of 

the sandstones and the presence of joints in all the varieties of rocks. 

Both these phenomena are exemplified strikingly in the conglomer-
30 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BULL.235.

o

ates, which often are divided into great blocks whose faces are nearly 

as smooth as if made by a'saw that had cut indifferently through the 

pebbles and their compact matrix.

The series is cut by many dikes and sheets of igneous rock; these 

are especially numerous along the main divide, where they must add 

materially to the volume of the formation. At three localities there 

are exposures of granitoid rock, apparently intrusive in the Pasayten 

formation. These igneous rocks will be described in another section.

TERTIARY FORMATIONS. . 

CLASSIFICATION AND DISTRIBUTION.

Tertiary rocks have much less importance along the boundary section of the Cascades than in central Washington. Of the formations 

to be described some are known positively to be Tertiary, while for 

others a Tertiary age is tentatively assumed on grounds that will be 

stated.

The areas of known and supposed Tertiary rocks, in the order in 

which they were seen, are as follows:

(1) Near Wenatchee there are exposed sedimentary beds that have 

been connected areally with the Swauk formation, of known Eocene 

age. With these are associated some andesite and rhyolite, and all 

these are overlain by the Miocene Yakima basalt.

(2) In Okanogan Valley, are extensive sedimentary and volcanic 

deposits, the structure and lithologic character of which indicate that 

they are not very old. They are supposed to be Tertiary.

(3) East of the great Cretaceous .area there is a belt of volcanic 

rocks which seem to overlie the Cretaceous and are tentatively 

referred to the Tertiary.

(4) In the western foothills of the Cascades and on the low coastal 

region there are great bodies of Eocene rocks, in part coal bearing. 

Exposures of these strata were seen in the vicinity of Hamilton and 

in the drainage basin of Nooksak River.

COLUMBIA RIVER VALLEY.

Swauk formation. The expansion of Columbia Canyon at Wenatchee, which has determined the location, of the town, owes its existence to the softness and consequent extensive erosion of the Swauk 

formation, which is splendidly exposed in the canyons southwestward from Wenatchee and on the slope facing that town across 

Columbia River. This 'formation, which is of Eocene age, has been 

ma.de the subject of detailed description in the Mount Stuart, Washington, folio by the senior author of this paper and needs to receive 

but brief description here.

As regards its lithologic character the Swauk of the Wenatchee 

basin consists for the greater part of sandstones, usually light colored
CALKINS:"] TERTIARY FORMATIONS. 31

and of arkose character. The. sandstones are frequently pebbly, 

however, and beds of conglomerate occur, in which the pebbles include 

light-colored rhyolite- and andesite-porphyries, quartzite, granite, and 

schist. Shales of variegated colors, including purple, red, green, gray, 

and-white, are abundant in the Swauk of this vicinity, notably across 

the Columbia from Wenatchee and in the canyons to the south. 

These colored shales are not represented in the Swauk of the Mount 

Stuart area. Plant remains are of frequent occurrence in the Swauk 

formation, and there are some beds of impure lignitic coal which have 

been prospected but. not found to warrant exploitation.

The relation of the Swauk formation to the basalt Avhicli overlies it 

is beautifully exposed in cliff sections on the sides of a gulch about 

3 miles south from AYena'uChee, where basalt gravel and basalt rest 

upon the truncated edges of folded sandstones that have a dip of 

about 45°. Farther west the angular unconformity is still greater, 

the sandstones having an inclination of 60°, while the overlying basalt 

is nearly horizontal.

. Andesite and rhyolite. Associated with the sandstones and shales 

of the Swauk formation near Wenatchee are volcanic rocks, probably 

in part intrusive and in part extrusive, belonging to the species rhyolite and andesite.

The andesite forms a rugged crag, prominent and of striking appearance, a few miles southwest of Wenatchee. Hasty examination of 

the occurrence led to the belief, based mainly on the absence of 

scoriaceous structures, that the rock is probably intrusive. The mass 

is in line with the axis of an anticline observed on the ridge south of 

it and may be of laccolithic nature. The rock shows lamellar and 

columnar jointing. It is in general much decomposed, but shows 

porphyritic texture, and on microscopic study proves to be andesite.

The rhyolites occur at two localities across the canyon south of the 

andesite crag. The first is at the edge of the alluvial flat where the 

rhyolite forms a small dome-shaped hill. The rock has here a pronounced lamination more or less parallel to the surface on all parts 

of the dome. It is mostly porphyritic, showing crystals of quartz and 

feldspar in a strong fine-grained groundmass, but there is some perlitic glass, breaking down into a coarse sand. Near the crest of the 

ridge south of the little dome there is another outcrop of rhyolite 

which overlies a bed of hard conglomerate and in part is massive, 

laminated, with distinct flow structure, and in part shows very beautifully the structure of a flow breccia. The rhyolite of this locality is 

doubtless extrusive and probably flowed in an old river channel, but 

the mass of rhyolite at the base of the hill seems more probably 

intrusive.

Yalcima basalt. The basaltic series overlying the Swauk formation 

at Wenatchee is the same that covers the greater part of eastern 

Washington and Oregon. Being the most important formation of the
32 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [nuiiL.235.

Pacific Northwest, it has received, notice from most of the writers on 

the geology of that region. In the Ellensburg and Mount Stuart folios 

of the Geologic Atlas of the United States it has been described with 

some detail by the senior author, and its characters need only be recapitulated briefly here. .

In the many splendid cliff exposures afforded by the erosion of the 

Columbia and its tributaries the series is seen to consist of many layers 

of lava and pyroclastic material. In some of the sections near the 

crest of the Cascades there is a large proportion of tuff, but in the 

vicinity of Columbia River the massive lavas are in decided preponderance. The most universal and striking structural feature of the 

 Yakiina basalt is the columnar jointing so characteristic of basalt in 

general. Amygdaloids and scoriaceous layers give abundant testimony to the extrusive origin of the series.

The route of the party to the region of the boundary lay in great 

part, near the edge of the basalt area. Table Mountain, which forms 

the northeastern rim of Kittitas Valley, is a structural uplift formed 

of basalt which is deeply intrenched by the Columbia along its eastern 

base. The north face of the mountain is a splendid erosion scarp, 

along the base of which the Swank formation is exposed. The surface north of the basalt cliff is of a peculiar hurnmocky character and 

has many undrained basins, its topography being evidently due to 

laudsliding from the precipitous slope. Large blocks of basalt are 

indeed found at some distance from the escarpment, toward which 

their bedding planes usually have a gentle inclination. The boundary 

between the basalt and the older formations swings away from the 

river opposite Wenatchee for a few miles, then again swings westward, 

so that the basalt forms the rim of the canyon of the Columbia as far 

( iip as the mouth of the Okanogan. From that point it extends in a 

northeasterly direction, and the formation is soon losl^to the view of. 

.the traveler proceeding up Okanogan Valley.

OKANOGAN VALLEY.

In Okanogan Valley, near Oroville, the slates and granites are overlain by sandstones whose structure and lithologic character indicate 

a comparatively recent age. These sedimentaries are overlain by 

andesites. . This group of beds is especially well exposed in the precipitous 

faces of the bold butte southwest of Loomis, known as Whitestone 

Hill. The height of the hill is about 1,300 feet above the alluvial 

deposits at its foot. Its base is composed of old rocks, presumably 

of the Cache Creek series, but the greater portion is built up of a succession of conglomerates, white sandstones apparently consisting in 

large part of volcanic material, and brownish and gray sandy shales. 

A thick capping of hornblende-andesite has been the agent in protecting these soft beds from erosion.
8c"t,Ki»s.D ] ''-" "" TERTIARY FORMATIONS. 33

In the basin north of Blue 'Lake, and in the valley of the SUnilkameen near its mouth, sandstones, conglomerates, and andesites, presumably of the same formation, are also exposed. (PI. II, A.) The 

conglomerates that were observed low down on the slope north of 

Blue Lake and that seem to be the sole, or at least the principal, 

representatives of the formation in Similkameen Valley are of somewhat remarkable character. They are generally very coarse and are 

especially characterized by the angularity of the fragments composing them. The materials are derived from the immediately underlying old rocks, and consist of slate, greenstone, granite, and schist. 

These are often intermingled, but some beds, especially those in 

Similkameen Valley, are composed solely of angular blocks of granite 

with a matrix of feldspathic sand and fragments of feldspar crystals. 

The section of Tertiary sediments in Similkameen Valley is illustrated 

in PI. II, A.

West of Lake Osoyoos the presence of abundant fragments of 

andesitic lava gives the material a tuffaceous appearance. .This 

green breccia and conglomerate also includes large bowlders of granite, and it is doubtless simply another phase of the Tertiary sediment. 

The andesite is both intrusive and effusive at this locality, and in the 

three exposures near Lake Osoyoos the andesitic lava rests unconforinably upon the sedimentary series.

Somewhat farther down the valley there are clastic beds which 

appear to be mainly tuffaceotis, and which are associated with considerable volumes of rhyolitic lava. The rhyolites are extensively 

developed a few miles north of Clover, between Salmon. Creek and 

Johnson Creek, and north of Johnson Creek. A specimen from the 

first-named locality proves, on microscopic study, to be asoda-rhyolite.

VOLCANICS EAST OF HIDDEN LAKES.

From the point where the Pasayten crosses the boundary a belt of 

volcanic rocks extends southeast with gradually increasing breadth. 

Along its eastern border the volcanic series rests upon granite. To 

the west it is in contact with and apparently overlies the sandstones 

of the Pasayten formation. The lithologic species represented in this 

volcanic area are (1) dacite, (2) hornblende-pyroxene-andesite, (3) 

basic pyroxene-andesite, and (4) hypersthene-basalt.

The dacite, which is a light-gray or drab rock containing rather 

abundant phenocrysts of quartz and feldspar with fewer of dark minerals, is mainly developed along the slopes southeast of the Hidden 

Lakes and also forms dikes in the Cretaceous sediments to the west/ 

The hornblende-pyroxene-andesite,- a dark-colored rock in which 

small black prisms of* the dark minerals are abundant, Avas collected 

in the eastern edge of the belt about 9 miles south of the boundary. 

The basic pyroxene-andesite which is exposed along the East Fork of 

the Pasayten and the most northern of the Hidden Lakes is a dark

Bull. 235 04 3
34 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BULL.235.

greenish rock somewhat resembling basalt, but distinguished by the 

presence of noticeably large porphyritic crystals of greenish feldspar. 

The hypersthene-basalt is a dense, fine-grained, dead-black rock 

containing large, conspicuous grains of yellowish green olivine. It 

forms a small knob on the slope east of the middle lake, standing up 

above the andesites, into which it appears to be intrusive.

WESTERN SLOPE.

Hamilton district. In the northwest part of the area of this reconnaissance there are important masses of Tertiary strata containing 

beds of coal, which have been prospected near Hamilton and in the 

valley of the Nooksak, without, however, any encouraging results. 

In 1895 some observations on these rocks were made in the vicinity 

of Hamilton, and some fossils were collected at the coal prospect 

known as the Skagit-Cumberland mine. The fossils collected at that 

time, and a collection made in the same vicinity by Prof. Henry 

Landes, State geologist of Washington, in 1901, have been examined 

by Dr. F. H. Knowlton, who reports that they prove the age of the 

beds to be Tertiary.

Nooksak Valley. A sedimentary series, possibly in part correlative 

with the beds of Skagit Valley, is exposed about the confluence of the 

forks of the Nooksak and also in the valley of the North Fork of the 

Nooksak below Glacier Creek. Professor Landes has also collected 

from these beds near Keese, obtaining some excellent material, which 

was submitted for examination to Do.ctor Knowlton, who reports that 

.much of this material is identical with or similar to forms from vein 

XII at Franklin, thus correlating the beds at Keese with the Puget 

formation, which is of Eocene age.

Lithologically the material constituting the Tertiary series of Nooksak Valley is chiefly sandstone, generally of light-olive or gray color, 

containing considerable amounts of feldspar and rock fragments. 

Some shale and conglomerate also enter into the constitution of the 

series. The character of the rocks shows that shallow-water conditions prevailed during the entire period of their deposition.

QUATERNARY FORMATIONS. 

CLASSIFICATION AND DISTRIBUTION.

. .The Quaternary formations of the region consist of the Mount 

Baker lava and of extensive stream deposits. The fresh condition 

and topographic relations of the lava show that it is post-Pliocene, 

and its considerable erosion and glaciation at Austin Pass show that 

it is also pre-Glacial. On the other hand, the^extensive deposits of 

sand, gravel, and silt in the valleys and mountain canyons and on 

the coastal plain were laid down by streams and glaciers in Glacial 

and post-Glacial time.
SCALKINS'D ] QUATERNARY LAVA AND STREAM DEPOSITS. 35

MOUNT BAKER LAVA.

Geologic relations. Mount Baker, like most of the higher peaks of 

the Cascades, is an extinct volcano built up of andesitic lavas of 

comparatively recent age. The mountain was not ascended by our 

party, but lavas that emanated -from the ancient crater were seen at 

Austin Pass and at a point in the canyon of Nooksak River almost 

directly north of the mountain. At the latter point the end of the 

flow forms a steep bluff on the south side of the river, but does not 

appear on the north side. North of Austin Pass a gray dome rises 

up above the. general height of the neighboring ridges, capped by 

purplish andesitic material, and this mass appears to have been an 

island-like projection of older rocks above the lava streams. East of 

the pass the lava overlaps vertical beds of sandstone and greenstone. 

The relations of the lava to the older terranes are interesting because 

they show that the lavas were poured out upon a topography as 

rugged as the present, and that the main drainage feature Of the 

region, the ISTooksak, had, at the time of their eruption, the same 

position, and even practically the same level, that it has now.

Litliologic characteristics. Although fragment al materials probably 

form part of the cone, all of the volcanic materials from Mount Baker 

observed at close range are lava. They present considerable variety 

in respect to the features observable in the field. In structure they 

vary from highly scoriaceous to compact, the latter, being always 

divided by joints either into prismatic columns usually standing 

nearly vertical, or into thin slabs more commonly horizontal. The 

first type of jointing is seen in striking illustration in the end of the 

flow that comes down to the Nooksak, and the second type is seen in 

the exposures at Austin Pass. The degree of crystalliuity also varies 

between wide limits; porphyritic texture is nearly always evident, 

but the groundmasses are in part evidently crystalline, in part distinctly glassy. The more crystalline varieties are generally of a gray 

color, while the more glassy phases are black, or, less commonly, red. 

The specimens collected are all to be classified as pyroxene-andesites, 

and thus belong to the type of lava most abundantly represented in 

the Pleistocene eruptions of the Cascade volcanoes.

GLACIAL AND STREAM DEPOSITS.

In describing the glacial and stream deposits it is convenient to 

make a geographic subdivision, considering in turn the deposits (1) 

of Columbia and Okanogan valleys, (2) of the mountain area, and (3) 

of the western area, including the coastal plain and the lower parts 

of Skagit and' Nooksak valleys.

Columbia and Okanogan valleys. The Pleistocene deposits of 

Columbia and Okanogan valleys record a most interesting Glacial and 

post-Glacial history, of which the principal episodes are, briefly, as 

follows: (1) Glaciation of the valleys; (2) melting and recession of
36 CASCADE '. RANGE NEAB FORTY-NINTH PARALLEL. [BULL.235.

glaciers and partial filling of valleys with gravel deposits from streams 

overladen with glacial debris; (3) reexcavation in the gravel deposits. 

"While it is not improbable that there was more than one advance and 

retreat of the ice, no definite evidence of this has been found.

The Pleistocene deposits in these valleys, then, may be classified 

according to origin as (1) deposits of Glacial age, including (a) true 

morainic accumulations and (b) aqueous deposits laid down by 

streams flowing along the sides of glaciers or in'ponds held back by 

ice dams, and (2) post-Glacial stream deposits.

The discussion of these deposits may well be prefaced by a brief 

resume of observations by earlier workers in this field:

Mr. Bailey Willis, in 1887, first called attention to the former existence of glaciers in the extreme northern part of Washington, either 

as portions of a general ice sheet or as tongues pushed forward from 

disconnected ice rivers descending from the north. a The glacial geology of northern Washington has since received attention from Russell, 6 W. L. Dawson, c Salisbury/* and others. It has been established 

by the observations of these writers that the Quaternary ice in northeast Washington was in the form of great valley glaciers which did 

not merge into a general ice sheet unless in the vicinity of the northern boundary. Upon the latter point some evidence will be presented 

on another page.

Of the great ice streams that existed in this region in Pleistocene 

time, probably the most important was that which flowed down Okanogan Valley. Professor Russell, 6 ten years ago, published .a vivid 

account of the impressive traces left by the Okanogan Glacier on the 

plateau embraced by the Great Bend of the Columbia. He noted the 

huge erratic blocks of basalt and granite, the glacial scorings on the 

bed rock, and the terminal moraine that sweeps across the plain. 

From his observations he deduced that a great glacier had once flowed 

down Okanogan Valley and, on reaching the Columbia, had divided,

one arm flowing down the valley of the master stream, the other and 

greater one crossing the 2,500-foot canyon and pushing south about 35 

miles farther.

In 1901 the terminal moraine was definitely traced by Messrs. George 

H. Garrey and Eliot Blackwelder. Its extent is indicated by Professor Salisbury/as follows: "The moraine of the ice lobe * .* * 

loops southeast from Chelan Falls to a point about 6 miles west ofv 

Coulee City, where it bends northeastward to a point 5 miles north of 

the city, on the bluff of the Grand Coulee." This description seems

a Willis, Bailey, Bull. U.-S. Geol. Survey No. 40, 1887, p. 10.

& Russell, I. C., Bull. U. S. Geol. Survey No. 108, 1893, pp. 25, 86-89; Ain. Geologist, vol. 22, 1898, 

pp. 362-369; Twentieth Ann. Eept. U. S. Geol. Survey, 1900, pp. 150-170. 

c Am. Geologist, vol. 22,1898, pp. 204-217. 

d Jour. Geol., vol. 9,1902, pp. 212-213. 

eBull. No. 108, loc. cit. 

/Jour. Geol., vol. 9, p. 721.
SCA INSD ] GLACIAL AND STREAM DEPOSITS. 37

to imply that the southern extension of the Okanogan 'Glacier was not 

bifurcated as Professor Russell suggested, but extended continuously 

from the Grand Coulee to the mountains west of the Columbia. The 

present depth of the portion of the Columbia Canyon that was occupied by ice is from 2,000 to 2,500 feet below the plateau to the south 

and east, and the elevation of the east end of the moraine as measured 

barometrically by the junior author in 1902 is about 2,200 feet above 

^sea level. If the inference from Professor Salisbury's statement 

given above is correct, it follows that there was at the maximum 

development of the Okanogan Glacier a thickness of something like 

2,500 feet of ice in the canyon of the Columbia between the mouth of 

the Okanogan and the Chelan crossing.

The authors of this report, in their course up Columbia and Okanogan valleys, had some opportunity to observe the evidences of their 

former occupation by ice. The most striking and unmistakable of these

evidences are the erratic bowlders, the remarkable accumulation of

which opposite the mouth of the Methow was first described by W. L. 

Dawson.® The western slope of the Columbia Canyon at this locality 

is strewn with great numbers of huge fragments of basalt and granite, 

many of them larger than the ordinary settler's cabin. They continue 

to occur along the left bank for some miles below this point, and a few 

are found on the Great Terrace above the right bank. North of the 

mouth of the Methow the slope of the valley has many erratics of 

basalt, although that rock does not occur in place on that side of the 

Columbia. The highest of these glacial bowlders for which a barometric observation is recorded is 1,100 feet above the river, but others 

in the vicinity lie, by estimate, at least 300 feet higher. These figures of course give minimum estimates for the thickness of the ice at 

this locality.

Along the sides of Columbia and Okanogan valleys there are numberless side channels of peculiar history, which will be described more 

fully in a later section. To the authors, both the form of these canyons and the character of the deposits on their floors seem to furnish abundant evidence that they had been occupied by ice. These 

deposits are characterized topographically by their hummocky and 

irregular surfaces, with numberless undrained basins and kettle holes. 

Most of: the channels in question are occupied by chains of lakes or 

ponds, while the small streams that flow through others meander 

through a succession of meadows, often finally disappearing beneath 

the porous deposits before reaching the master streams.

Professor Russell has noted accumulations of such character in 

Antoine Coulee south of Methow River, but considers them to be 

merely talus. 6 To the authors of this bulletin these accumulations, 

while doubtless comprising much talus material, seemed to be so

aLoc. cit., p. 215. b Ata. Geologist, vol. 22, p. 307.
38 CASCADE KAJSTC4E WEAK FORTY-NINTH PARALLEL. [iWLi,235.

voluminous and of such topographic form that they could not be 

accounted for except as morainal deposits. Moutonnee surfaces of 

granite were observed projecting from the terrace north of this coulee, 

and on the southern wall of Peters Canyon, which joins it at the other 

end. Professor Russell's contention that the ice did not reach an 

elevation as high as the bottom of the channel seems to be quite 

invalidated by the fact that the highest point in the bottom of the 

coulee is only about 700 feet above the river, while glacial bowlders 

were observed about o miles north perched upon the canyon side 400 

feet higher.

Closely related to the morainal deposits above described are numerous bowlders of schist and granite strewn upon the low terraces at 

Wenatchee, of so great size that they could only have been transported 

by ice. They are supposed to have been carried to their present position by icebergs broken from the front of the Okanogan Glacier.

Upon the sides of the canyon of the Columbia are a succession of 

terraces, in part benches'carved from bed rock, but mainly fill terraces 

built of stream-laid rounded gravels. From a point near the mouth 

of Knapp Coulee to the mouth of Okanogan River one of these gravel 

benches is markedty distinguished from all the others by its extent 

and perfection, and has been designated by Professor Russell the 

" Great Terrace of the Columbia." There are other benches of minor 

extent above and below the Great Terrace. The Great Terrace itself 

and those below it are of 'post-Glacial age, while those above it are 

believed to be contemporaneous with the glacial occupation of the 

valley. In order of age, then, the higher terraces will be described 

first.

From a point of view near the southern end of Antoine Coulee the 

observer may see, on the opposite side of Columbia Canyon, at least 

ten unmistakable, though often rather indistinct, benches above the

level of the Great Terrace. The junior author examined the slope

north of Ives and found it largely covered with soft sand and gravel 

and broken by a series of terraces, of which the highest recognized 

was about 2,300 feet above the water level at the mouth of the 

Methow. These high terraces seem to have been either ignored or 

passed over briefly by previous writers," but they should be considered 

in any attempt to construct a complete history of Columbia River. 

They are attributed to the period when the valley was occupied by 

ice, the hypothesis being based upon the position of the terraces, 

their form, and the character of the materials composing them. The 

highest terrace is apparent!}' at the highest level which the surface of 

the ice attained, according to the evidence of the terminal moraine, 

and the fact that many of them are on that part of the slope strewn

a Salisbury and Willis examined in 1900 similar terraces above Chelan Ferry, and considered 

them to be in part stream terraces, indigenous to the brooks that now cut them, and in part 

moraine terraces of small glaciers that formed from snow drifted over the scarp of the plateau. 

Communication from Mr. Willis.
S c" TLfIciAN8D ] GLACIAL AND STREAM DEPOSITS. 39

with glacial bowlders precludes the supposition that these features 

are pre-Glacial. It appears, on the other hand, utterly improbable 

that they are of the nature of the Great Terrace and prove a filling 

of the valley with stream deposits to a depth of over 2,000 feet. As 

regards their form, they are less regular than the lower benches, and 

characterized by more numerous deep pittings than on the Great 

Terrace. The pebbles and bowlders entering into the construction 

of the terraces are generally subangular, suggesting glacial debris 

only slightly worked over by water. The facts of observation, therefore, are taken to indicate that the high terraces were built by streams 

flowing along the sides of the Okanogan Glacier during the period of 

its decline.

Probably to be correlated with the features just considered are the 

deposits of unconsolidated sand and gravel which mantle the slopes 

carved from the old rocks in the basin east of Loomis in which Whitestone Hill arid the Spectacle Lakes are situated. The maximum elevation of these beds just east of the low pass between this basin and the 

canyon of the Simlahekin is not less than 700 feet above the nearest 

point on Okanogan River. a It is supposed that these deposits belongto a period, when the main Okanogan channel was filled with ice, 

which acted as a dam and formed a great pond in this lateral basin.

Extensive high-level deposits of coarse gravel in Peters Canyon 

between Methow and Chelan rivers ar,e described by Professor Rtissell b and were observed by the authors. Opposite the southern end 

of Antoine Coulee a barometric reading, checked on a near bench 

mark, gave the elevation of the upper surface of these gravel deposits 

as 1,820 feet, which is about 1,100 feet above the nearest point of 

Columbia River.

W. L. Dawson observed these deposits in 1896, and in explaining 

their origin says that they "were evidently accumulated at a time 

when the occupation of the Columbia gorge by the still moving Okanogan Glacier prevented the free escape of drainage waters." 6

Professor Russell rf does not adopt this explanation, but says: "As 

the locality is, by estimate, about 4 miles from the Columbia, it would 

seem as if the gradient of the stream which deposited the gravels was 

sufficient to account for their elevation above that river." It seems 

to be implied that the deposits in question are an extension of the 

Great Terrace, whose nearest point is probably not more than 2 miles 

from the locality where the deposits of Peters Canyon attain a height 

of 540 feet above it. It is difficult to imagine a stream of such a gradient as 270 feet to the mile depositing ah important body of gravel. 

In objection to the hypothesis advanced by Dawson, it is urged by 

Professor Russell that no evidence of a sufficient thickness of ice in

a Based on barometric readings and surveys of the Great Northern Railroad. 

6Qp. cit., pp. 180-182. 

cAra. Geologist, vol. 22, p. 212. 

. cit., p. 181.
40 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BULL.235.

the valley of the Columbia has been obtained. Reasons foi' disagreement with the latter statement have been given on preceding pages, 

to which the reader is referred. The authors are therefore inclined 

to accept the explanation advanced by the first observer and to consider the gravels at Peters Canyon as in the nabure of a delta deposit 

laid down in a tributary canyon dammed by the Okanogan Glacier.

The Great Terrace is first clearly recognized by the traveler going 

north from Wenatchee about 3 miles beyond Entiat. For several 

miles northeast of that point it is well developed along the left bank 

of the river, and is shown by the contours on the Chelan topographic 

sheet of the United States Geological Survey. It is also in general 

well marked all along the west side of the valley from Chelan nearly 

to the Okauogan. The Great Terrace naturally extends up the tributaries of the Columbia, and in the lower portion of Okanogan Valley 

attains a breadth greater than the maximum observed along the 

master stream, amounting perhaps to as much as 3 miles just northeast 

of Brewster and about the same a few miles north of Clover.

The height of the Great Terrace above Columbia and Okanogan 

rivers was measured barometrically by the authors at several points. 

The results are of interest as giving some indication of ,the relative 

grades of those stream? at the present time and at the time when the 

terrace was formed.

Barometric measurements of the elevation of the Great Terrace above Columbia

and Okanogan rivers.

No.

1

9,

3

4

r>

r>

7

8

9

10

Locality.

Mouth of Knapp Coulee ..................................

Howard Flat ............... .............................

.....do ...................................................

Near Ives, brink of terrace ...-......-.---.-..--.-.--......

....do..... '..............................................

Near Ives, one-half mile from brink. ......................

Brewster . .....-...--...-......-..-.-.. ...... ......_.-.....

North of Ophir __.____._ ._..__...__..._..__.____..._ . .____

North of Clover, back of terrace, 2 or 3 miles from river. ....

Approximate 

height.

' Feet. 

528

520

505

460

465

490

470

320

390

345

Observer.

G.O.S.

G.O.S.

F. C. C.

G.O.S.

F.C.C.

F.C.C.

G.O.S.

G.O.S.

F.C.C.

F.C.C.

On comparison of the observations it is at once evident that, neglecting small discrepancies and allowing for the slope from the back 

of the terrace, illustrated by observations 5 and 6, the difference 

between the present water level and the Great Terrace decreases as 

we go upstream. It is thus proved that the old gradient of the
S n!T*it« CALKINS.D l GLACIAL AND STRP;AM DEPOSITS. 41

Columbia and bkaiiogan was less than the present gradient, unless 

there has been post-Glacial deformation, . As regards its origin, this remarkable feature is evidently constructional. The slope from its brink to the river is composed entirely of 

gravel, and the Columbia, within the area considered here, either 

flows on gravel or has intrenched itself but slightly in bed rock. It 

follows that the bed-rock canyon of the Columbia, practically as deep 

as the present one and broader bottomed, was once filled with fluviatile 

deposits at least to the level of the Great Terrace. That level, furthermore, probably marks the upper limit of post-Glacial filling, for 

there are no extensive terraces above it. The benches below the 

Great Terrace simply mark pauses in the process of clearing out the 

gravel deposits, to which the stream has mainly devoted itself in late 

Quaternary time.

Mountain area. In the mountain valleys the authors made few 

detailed observations in regard to glacial deposits. The evidence 

that the principal mountain valleys were once occupied by ice consists principally in the- characteristic erosion forms produced by 

glaciers. Stream erosion has been active in post-Glacial times, so 

that the morainal accumulations have been largely removed and 

redistributed as flood-plain deposits. Locally, however, the.materials 

in the valley bottoms show the hummocky arrangement that is characteristic of glacial deposits. The great majority of. the numerous 

lakes of the region owe their existence to glacial action. In addition 

to the multitudes of rock-rimmed tarns that lie in the abandoned high 

cirques and glacial benches, there are in the deeper valleys several 

larger bodies of water, such as Hidden Lakes, that have morainal 

dams. Dr. R. A. Daly rt notes that Chilliwhack Lake, which was not 

visited by the authors of this paper, is held by a moraine.

Although no well-defined lateral moraines were seen by the authors, 

erratic bowlders were noted on some of the valley walls. Two 

observations were made near the international boundary which may 

bear upon the question of the southern extension of the Cordilleran 

ice sheet. Directly* west of Mount Chopaka, on the southern slope 

of the divide extending westward from that peak, some blocks of 

granite were found in a position to indicate that they had been transported from the northern slope. The size of these erratics necessitated ice transport, and the locality is such as to preclude the work of 

any valley glacier. It seems probable, therefore, that the ice sheet 

here extended a few miles south of the forty-ninth parallel and 

attained an elevation of about 6,500 feet. Again, in Pasayten Valley granite blocks were found 1,000 to 2,000 feet above the river level, 

on the tops of ridges. Glacial bowlders, presumably left by the valley 

glacier, occur on the lower slopes, but these higher-level erratics were 

thought to be possibly of different derivation. Unless there is gran-

« Summary Report Geol. Survey Canada, 1901, p. 43.
42 CASCADE RAWGE NEAR FORTY-NINTH PARALLEL.

ite occurring at points at the head of this valley not visited, these 

granite bowlders must have come from the north, where the granite 

extends down to the river level. These two occurrences of glacial 

erratics with a possible northern derivation are quite in accord with 

the southern limit of the ice sheet as mapped by Dawson.

As in the larger valleys to the east, glacial debris accumulated 

when the glaciers were extensive and probably overloaded the streams 

in the period following. The small high-grade streams of the mountains are bordered by gravel deposits of considerable importance. 

West of Toats Coulee Creek, near the opening of the Horseshoe, there 

is a gravel terrace more than a hundred feet above the stream and 

several hundred yards in width, while the valley of the stream draining the cirques of Bighorn Peak contain similar accumulations, which, 

through the present stream channel, has been excavated. The flatbottomed valleys of the Pasayten and its principal forks are floored 

with gravel deposits of great lateral extent and considerable thickness, which have been carved into terraces. Near the boundary, on 

the main stream, two gravel benches were noted at 80 and 150 feet, 

respectively, above the stream, which has not reached bed rock.

High-level gravel terraces are found in protected localities along 

the steep gorge of Ruby Creek, but are developed extensively only 

near its mouth, where it really flows across a portion of the broader 

U-shaped valley of the Skagit before joining the main stream. The 

gravels here lie on a high shelf in the bed rock, the creek itself flowing in a narrow canyon intrenched in the gneiss; gravel deposits are 

also spread upon the floor of Skagit Valley above the junction.

Western area. On the western side of the Cascades it is still more 

difficult than in the mountain area to separate glacial from fluviatile 

deposits. Below the point where the Skagit emerges from its splendid 

gorge gravel terraces are found on either side, and become of increasing importance as one continues downstream. The valley becomes 

constantly broader and at Hamilton has widened to an alluvial plain 

several miles in breadth.

Along Nooksak River, especially between Keese and Maple Falls 

and for a few miles above the latter point, there are broad gravel 

terraces, of which the highest are not less than 200 feet above the 

river. For many miles also below Shuksan the road is laid upon a 

terrace which is not high above the water level. Above Shuksan 

gravel deposits are not so important, and the stream channel is generally in bed rock. Below that point there are rock gorges at the 

Falls and other points, and near the junction of North Fork and 

Middle Fork at Deming the bank of the North Fork is a bluff of 

Tertiary sandstone.

In the lowlands adjacent to the coast, in the western portion of the 

area traversed in this reconnaissance, there are extensive deposits of 

gravels, sands, and silts, which are in part continuous with the 

deposits of the western valleys. Much of this material possesses
INTRUSIVE BOOKS. 43

characters that testify to its glacial origin, but some of the gravels 

.are typical stream deposits. The topography is generally of the lowplateau type, only a hundred feet or so above sea level, these higher 

flat-topped, features being diversified with swamps and separated by 

broad flood plains.

The higher areas are composed generally of coarse, well-washed 

gravels, as shown in stream cuts or shore cliffs, but on the surface the 

soil, where not concealed by vegetation, has till characters. There is 

every indication that these surficial deposits near the boundary are of 

the same origin and record much the same Pleistocene history as those 

farther south in. Puget Sound basin/' The gravel plains and alluvial 

bottoms represent the constructive work of streams, the former being 

more of the nature of low delta deposits and terraces built up in the 

vicinity of a large piedmont glacier. The till which covers many of 

these gravel plateaus was deposited at times of glacial advance, and 

in some localities moraines and other features of relief occur which 

are plainly the work of ice. The interaction of ice and stream work 

has been productive of considerable variety of minor features, the 

understanding of which would necessitate detailed observations.

INTRUSIVE ROCKS. 

PRELIMINARY STATEMENT.

Q-eneral classification. Granular igneous rocks, intruded into older 

sedimentary formations and solidified under great masses of strata 

that have since been removed by erosion, occupy a greater proportion 

of the area examined in this reconnaissance than do all other classes 

of rocks combined. Of much less geologic importance, yet very generally distributed, are igneous dikes of various composition which cut 

both the plutonic and the stratified rocks. These usually appear to 

have direct relation with the great plutonic masses.

The plutonic rocks might readily be divided by the nonpetrographic 

observer into two groups. The first, which has by far the less import-, 

ancein this region, comprises the rocks characterized by petrographers 

as "basic" and "ultrabasic." They include diorite, gabbro, pyroxenite and peridotite, and serpentine, which is formed by the alteration of the last-named rock. These are distinguished by dark color 

and high specific gravity, due to the predominance of dark minerals 

rich in iron and magnesia, and to the subordination or absence of 

quartz and the feldspars.

The second group, the representatives of which have an enormous 

development in the Northern Cascades, consists of comparatively lightcolored rocks, of which the principal constituent is feldspar, and in 

which quartz plays an essential part, generally being visible to the 

naked eye. These rocks have mostly been designated on the map, in 

a general way, as "granitic rocks," and most of them would probaA full description of'these is given by Willis and Smith in the Tacoma folio, No. 54, Geologic 

Atlas of United States.
44 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BULL.236.

ably be called "granite" by a nontechnical observer, using the term 

in a loose sense. In fact, however, the group includes three species 

(granite, granodiorite, and quartz-diorite), sufficiently distinct to be 

generally separable in the field. It seems advisable, therefore, to , 

recognize these divisions in the following pages, and, instead of 

using "granite" or "granitic" rocks in a popular sense, to employ 

specific names defined in terms of features recognizable in the field by 

a person acquainted with the rudiments of mineralogy. Additional 

reason for using petrographic names lies in the fact that this description of the areal and geologic relations of the plutouic rocks 

must serve as an introduction to their petrography. A too broad use 

of terms at present would necessitate much repetition later. The 

dike rocks, however, being fine grained and often only determinable 

l>y microscopic study, must frequently be designated in less definite 

terms, and on account of their small .geologic importance will not 

receive extended consideration here.

Method of treatment. For the general consideration before us it 

seems best to adopt an arrangement based on geographic distribution 

without regard to petrographic classification. The principal intrusive 

masses will therefore be considered in the order in which they were . 

encountered during the progress of the reconnaissance.

ALONG THE COLUMBIA.

Megascopic features of granodiorite. In the valley of the Columbia 

there are extensive masses of granular rock of a type that attains 

enormous development in the Sierra Nevada, where it has been given 

the name '' granodiorite." The characteristic features of this rock visible in the field are as follows: The color of large masses viewed at a 

distance appears rather light gray. On closer inspection this hue is 

found to be due to the combined effect of a mixture of a relatively 

small proportion of dark-colored minerals with a preponderant amount 

of light constituents. Of the latter class decidedly the greater part 

is feldspar, usually clear white and distinguished by its cleavage from 

the more transparent, irregularly fractured quartz. Quartz, though 

subordinate to feldspar, is an important constituent, easily recognizable on close examination. The dark minerals are hornblende and 

biotite; the former, the color of which is greenish black, forms 

roughly prismatic individuals Avith cleavage in two intersecting sets 

of planes parallel to the direction of elongation; the latter, which is 

deep "brown in color, forms tablets or short prisms characterized by 

the well-known micaceous cleavage. These dark minerals are usually 

present in about equal quantities, although biotite predominates in 

certain lighter-colored varieties. a

a This brief characterization is not intended as a general definition of the term "granodiorite," 

its purpose being merely to aid the lay reader to recognize the rock under description in the 

field. The specific character of the feldspars is not mentioned, because not determinable megascopically. The description given applies to all the granodiorites of this -region and is believed 

adequate to distinguish them from the other rocks of the region. The definitions in this chapter of other rocks will be constructed with a similar purpose in view.
S cA ms.D ] INTRUSIVE BOOKS. 45

'Occurrences of granodiorite. Of this nature was the first plutonic 

mass encountered, Avhich extended along the route from Entiat to 

Knapp Coulee. At neither limit were the contacts with the adjacent 

rocks directly observed; the greater age of the rocks on either side 

of the granodiorite is sufficiently proved, however, by the evidence 

of extreme metamorphism in the former, in contrast to the absence 

of foliation or other evidences of dynamic action in the granodiorite.

In the neighborhood of the southern boundary there is additional 

evidence of this rock's intrusive nature. The schist and gneiss forming the walls of the gorge below Entiat are cut by a multitude of 

white, coarse-grained pegmatite dikes, whose increasing abundance, 

as the granodiorite is approached, strongly points to their genetic 

relationship with that rock. Other dikes appear within a few miles 

of the contact,- which may be grouped as basic and acidic. The 

former are dark colored, with feldspar crystals sometimes standing 

out from the general mass, but generally not prominent. The acidic 

rocks are fine grained, but evidently crystalline, and.show inconspicuous phenocrysts of feldspar and quartz in a white groundmass. 

These complementary dikes cut the great granodiorite mass as well 

as the schists.

Near the northern boundary of this mass there is a zone in which 

the abundant dark-colored rocks rich in hornblende are mingled in 

the most intricate manner with light-colored material similar to the 

granodiorite of the main mass, or in part even more acidic.

From a short distance above Lake Chelan nearly to the mouth of 

the Methow the country rock is granodiorite similar to that just 

described. It may be that these two areas, separated along the route 

by schist, are connected farther west. This mass is evidently intrusive into the schists on the north, and the contact zone is characterized by abundant hornblendic material such as was mentioned in the 

last paragraph.

OKANOGAN VALLEY.

Grrcmiiic and dioritic rocks. In the southern portion of Okanogan Valley occurs a more siliceous rock, which it is thought may 

properly be designated granite. This granite is very light colored, 

owing to the very insignificant role of the dark minerals, the only ones 

visible in the hand specimen being a little light-brown titanite and 

dark-brown biotite; there is also a little white mica. Quartz is very 

abundant, and among the feldspars large crystals of orthoclase having 

a faint rose tint are conspicuous.

In the vicinity of Clover post-office rocks of two distinct types are 

developed, both of which are probably younger than the schists of 

that district. The first of these is dark gray and dioritic in aspect, 

coarse grained, except at its irruptive contact with the schists, and 

generally shows a more or less pronounced foliation. On certain .glaciated surfaces on the ridge south of Clover this rock is seen to be full 

of darker blotches of more basic material which have been drawn out
46 CASCADE EA1STGE NEAE FOBTY-HTNTH PARALLEL. [BULL.235.

into lenticular forms by the same forces that have produced the 

gneissic lamination of the general mass. Petrographically this rock 

is closely related to the granodiorite, differing from it in containing 

a large proportion of hornblende and a smaller amount of quartz. It 

is to be classified as a quartz-diorite.

The other rock is a coarse pink granite, containing a small amount 

of biotite and an abundance of quartz. The relation of this graniteto the sheared diorite was not made out with certainty, but the evidence obtained seemed to indicate that the granite is intrusive in the 

diorite. The two rocks are contrasted in petrographic characters, 

and no transition between them could be made out such as would 

indicate that they were produced by the differentiation of a single 

intrusion. No dikes of one within the other were observed in place, 

though a block of the diorite was seen to be .penetrated by a dikelet 

of fine-grained light-colored granite. The relative distribution of 

the two rocks and the absence of gneissic lamination in the more 

acidic granite also seem to confirm the supposition that the latter is 

the younger.

A few miles south-southwest of Lake Osoyoos there is a 'comparatively small mass of granite bounded on the south, west, and north 

by slates and schists, and on the east by the Okanogan terraces, 

though it continues across the river to the east. This granite is 

undoubtedly intrusive in the slaty rocks, which generally show considerable metamorphism near its boundaries and are cut by dikes of 

pegmatite.

In mineralogic composition it resembles the granites seen farther 

down the valley. The color is in general decidedly pinkish. The 

most characteristic feature consists in the presence of abundant large 

pheuocrysts of orthoclase feldspar, which are often more than an inch 

in. length.

Along the route from a little north of Cohconnully to Fish Lake 

there are extensive exposures of quartz-diorite, similar to that at 

Clover, but generally finer grained. Farther north this diorite gives 

way to granodiorite and true granite. The character of the transition 

was not studied. The rock may indeed be merely a marginal phase of a 

large mass, for these exposures are along the border of the great area 

of acidic plutonic rocks from which Okanogan Mountains are carved.

.G-abbro and diabase near Loomis. To the north of Loomis is developed an intrusive rock more basic than any heretofore noted. In its 

finer grained phases it appears almost uniformly dark green in color, 

and the constituent minerals are not readily distinguished. Where 

-it is more coarsely crystalline, however, as just east of the foot of 

Palmer Lake, it is seen to consist essentially of large lath-shaped 

feldspar crystals embedded in a dark crystalline material, which 

microscopic study shows to be pyroxene partly altered to amphibole. 

The finer grained rock is to be classified as diabase, and the coarser 

as gabbro.
I INTEUSIVE EOCKS. 47

These rocks are chemically similar to the old lavas of the supposed 

Cache Creek beds. They appear also to be connected with them, and 

although the relation has not been demonstrated it -appears highly 

probable that the diabasic rocks in question represent the partly 

unburied roots of the ancient volcano from which the Cache Creek 

extrusives were poured forth.

OKANOGAN MOUNTAINS.

Ultrdbasic intrusives of Mount Chopaka. Mount Chopaka, which 

overlooks the boundary at the eastern border of the Okanogan Mountains, is carved from a more or less complex series of dark-colored 

basic rocks. The summit is an altered dark gray-green gabbro. On 

the east and north slopes are excellent exposures of dark-green compact serpentine with a sprinkling of lustrous pyroxene crystals, and 

some coarsely crystalline rocks, consisting mainly of pyroxene and 

amphibole. All these rocks are evidently much altered. Their relation to the supposed Cache Creek rocks was not observed.

Composite character of the granitic belt. The Okanogan Mountains 

at the boundary are almost coextensive with a great belt of plutonic 

rocks extending from a few miles west of Lake Osoyoos to the Pasayten River. This great mass is by no means homogeneous; while 

composed chiefly of granite and allied rocks, it comprises important 

masses of granodiorite and more basic types that have local development. The hasty character of our work made it impossible to separate 

these species on the map, even roughly. In the following paragraphs, 

however, the general distribution of the principal types will be 

indicated.

Biotite-granite. The largest part of the plutonic rocks of the Okanogan Mountains may be classified as biotite-granites. The rocks 

assigned to this class are all characterized by having biotite as the 

dominant ferromagnesian constituent, although they sometimes contain an insignificant amount of hornblende or of muscovite. The 

biotite-granites prevailingly show the pink color characteristic of 

many granular rocks rich in orthoclase, this being often developed 

porphyritically, as in the similar rocks of Okanogan Valley.

As to its areal distribution, the biotite-granite appears to be the 

dominant type throughout the northern part of the 10-minute strip, 

except for its interruption by a belt of light-colored granite between 

Cathedral Peak and Ashnola River. Although the southern portion 

is mostly occupied by other types, the biotite-granite extends south of 

the 48° 50' line approximately from the longitude of Bighorn Peak to 

the stream flowing southeastward from Mount Remmel. It is especially well exposed on the northern slope of the Horseshoe and in 

Cathedral. Peak and the neighboring elevations.

Granodiorite. This rock has its most extensive development in. the 

area south of the Chopaka group of peaks and of the Horseshoe. It 

has the same general characteristics as the similar rocks along Colum-
48 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BULL. as.

bia River, and is distinguished from the biotite-granites by its gray 

tint, in contrast with the pink tones of the latter, and by its prominent 

hornblende crystals.

In addition to the main area, the granodiorite forms the triangular 

area west of Haipwil Lake and the tongue-like projection from the 

main mass to the north. There is also a small area of similar rock 

southeast of Park Pass.

The geologic relationship of the granocliorites to the biotite-granites 

was in no case definitely ascertained. On Horseshoe Mountain, where 

the contact between the two rocks is exposed on glaciated surfaces 

somewhat defaced by weathering, the conditions appear most favorable to the hope o£ determining this important question, but.this 

hope was not fully realized. At the best exposure there seems to be 

a rapid gradation between the two rocks, which, however, show their 

typical aspects within a few feet.of each other.

Diorite of the Horseshoe. Mention may be made here of a comparatively small mass of fine-grained diorite, apparently an elongated 

oval in plan, which lies between the granodiorite and biotite-grauite 

at the east end of the northern spur of the Horseshoe. The relation 

of this rock to those with which it is in contact is obscure.

Biotite-muscovite-granite. The third well-defined type represented 

in the great granite area was first met with just west of Cathedral. 

Peak, where its contrast with the pink coarse-grained biotite-granite 

was immediately evident. The rock is fine grained, pale gray in gen- 

'eral tint, and carries small quantities of both black and white micas, 

with small red garnets often visible. A gneissic banding is very commonly developed, but not universally. The coarse pink granite comes 

in again as the country rock west of Ashnola River, but the lighter 

colored two-mica granite reappears near the southwest corner of the 

10-mrnute strip across the main granite belt. The peak 3 miles southsoutheast of Park Pass is composed of somewhat similar granite, 

changed by pressure to a well-foliated gneiss.

Dike rocks of various kinds occur in association with all the plutonic rocks of the Okanogan Mountains. Perhaps the most common 

are aplites light-colored rocks which are essentially fine, even-grained 

mixtures of feldspar and quartz. Of similar composition, but different texture, are the pegmatites, in which the feldspar crystals are frequently of great size. Various basic dike rocks occur also, usually 

dark gray-green in color, sometimes porphyritic and sometimes of 

fine, even texture. The granodiorites southwest of Chopaka have sent 

tongues into the quartzitic schists, and have the same composition as 

the granodiorites, but are of porphyritic texture, and are therefore 

designated granodiorite-porphyries.

In the granite north of Park Pass there are dikes of a very darkcolored, .rather coarsely crystalline rock which attracted notice in the 

field from its decided effect on the magnetic needle of the plane table.
SMITH A 

CALKINSs.D ] INTRUSIVE BOOKS.

HOZOMEEN RANGE.

Quartz-diorite. The Hozomeen Range presents a contrast to the 

Okanogan Mountains in the subordinate role which is played in its 

constitution by intrusive rocks.

Two small masses of quartz-diorite practically identical in constitution were observed. The most striking megascopic feature distinguishing this rock from the granodiorites is the darker gray color, 

which is due to the greater, abundance of hornblende. Feldspar is 

the most abundant constituent; quartz and biotite, though present, 

are inconspicuous.

This rock was observed in a small outcrop southwest of Hidden 

Lakes, in the Okanogan Mountains, and a mass about half a mile in 

diameter is cut into by Ruby Creek just below the junction of Slate 

and Canyon creeks, on the western slope of the Hozomeen Range. In 

both cases the areal relations seem to indicate that the diorite is 

intrusive in the Cretaceous sediments.

Serpentine (saxonite). On Ruby Creek below the mouth of Granite Creek there is exposed a mass of dark greenish granular rock 

which may be classified roughly as serpentine, or, more accurately, 

as altered saxonite. This rock was observed by Professor Russell 

and indicated, not very accurately, on his map. It is apparently 

intrusive in the gneisses coming in just to the west of Granite Creek. 

These can best be described a little further on in connection with the 

great plutonic areas of the Skagit Mountains with which they are 

connected.

Dike rocks. Along the main crest of the range, near Barren and 

to the north, the Cretaceous sediments are cut by a multitude of 

dikes comprising a wide variety of lithologic types, including lightcolored quartz-porphyries, dark even-grained diabase, and basic 

porphyries in which crystals of hornblende and pyroxene stand out 

prominently. The 8,000-foot .peak southwest of Hidden Lakes also 

is ribbed with acidic and basic dikes. It is possible that these dikes 

have some genetic relationship to the quartz-diorite masses already 

noted'. Professor Russell has recorded.his observations on dikes in 

the vicinity of Barrou and on others in Methow Valley" which may 

'be related to these.

SKAGIT VALLEY AND SKAGIT MOUNTAINS.

Eastern portion. Near the north-south stretch of Skagit River the 

party reached the eastern boundaiy of a broad zone of granitic rocks, 

comparable in extent to that which forms most o^ the Okanogan subrange and extending west to the longitude of Mount Shuksan. This 

broad granite belt is by no means simple in its nature, but includes 

various types of rock which probably represent several intrusions of 

widely different ages.

« Twentieth Ann. Kept. U. S. Geol. Survey, pt. 2, 1900, pp. 115,116. 

Bull. 235 04 4
50 CASCADE .RANGE NEAR FORTY-NINTH PARALLEL. [BULL.235.

The valley of the Skagit near its junction with Ruby Creek is 

floored with gray coarse-grained gneiss, distinctly foliated, but evidently produced by the action of pressure on a plutonic rock allied to 

granodiorite. Farther up the valley there occur finer grained rocks., 

not foliated-, which are in all probability much younger than the 

gneiss. Although no actual contacts were observed the areal relations appeared to indicate that this mass was intrusive in the Cretaceous, and is probably to be correlated with the quartz-diorite mass 

near the junction of Canyon and Ruby creeks. Petrographically the 

rocks are similar, but the Skagit River material is slightly more 

siliceous.

For some distance west of the mouth of Ruby Creek .the gneissic 

formation is complex, and contains streaks of dark schists apparently 

representing old rocks into which the igneous magma forming the 

main mass was intruded. Beyond Goodell's ranch some nonfoliated 

younger-looking granodiorite was observed.

Western portion. No important masses of plutonic rock were seen 

along the route from Marblemount to the Mount Baker mining district. According to Dr. R. A. Daly,ft however, granitoid rocks extend 

along the international boundary to the crossing of Silicia Creek. 

They are mainly characterized, according to him, by the presence of 

biotite and hornblende, which become so abundant near the western 

border of the area as to give the rock a dioritic appearance.

The writer was able to make some observations on the plutonic 

rocks exposed along Silicia Creek and in the vicinity of Mamie Pass. 

This granite is irruptive into the schists that form the country rock of 

the mines in the Mount Baker district, the relation of the intrusive to 

the sediments being very clearly displayed at the Mamie Pass locality. 

This locality is of peculiar interest owing to the variations exhibited 

there by the igneous rock near the contact. While a few hours' 

examination was, of course, quite insufficient for a thorough study of 

the phenomena, the main facts appear to be as follows:

The normal character of the magma appears to be represented by 

specimens collected at Mamie Pass and along Silicia Creek, where the 

rock was observed at a distance from any contact and. is uniform 

over considerable distances. This normal type is a rather light-gray, 

medium-grained, evenly granular rock, in which the main constituent 

is white feldspar, but in which quartz is'fairly prominent megascopically. The characteristic dark mineral is biotite, but a little hornblende occurs locally. The character of the feldspars, which is not 

evident megascopically, places this rock among the granodiorites, 

but it approaches the true granites more closely than the granodiorites 

already described.

The modifications of this primary type are both chemical and 

structural in their nature, but the chemical variations, which are

a Summary Report Geol. Survey Canada, 1901, p. 47. ' .
PETROGRAPHY. 51

recognizable in the field by the "variations in. mineralogic character, 

are the more important. The most significant fact seems to be the 

universal presence of more basic rocks between the normal granite 

and the surrounding schists. The material generally found near the 

periphery of the mass is darker colored than the rock just described 

by reason of a higher proportion of iron-bearing silicates, among 

which-the hornblende assumes a prominent role, becoming equal to 

or greater than the biptite in amount, while the quartz becomes 

inconspicuous or absent. The most abundant types of the peripheral 

zone are diorites and granodiorites, but there are subordinate amounts 

of even more basic material in which the dark ferromagnesian min-' 

erals are more abundant than the feldspar.

The rocks of this plutonic mass are generally distinctly granular 

and moderately coarse grained. Textural modifications occur, however, as illustrated by a granodiorite-porphyry occurring on the summit of Granite Mountain, and a fine-grained phase of the acidic 

granodiorite appearing on its southern slope.

The granular rocks are cut by dikes, from which were collected 

specimens of fine white aplite, a white granite-porphyry with strikingly 

rounded phenocrysts of quartz, and a dark fine-grained rock showing 

interesting microscopic features that will be described later.

PETROGRAPHY.

INTRODUCTORY STATEMENT..

A detailed account of the igneous rocks of the region would not be 

included properly in a report of this kind, nor do the writers possess 

sufficient material for such an account. Opportunity was not had to 

make a fully representative collection, and many interesting occuri-ences of igneous rocks, the close study of which may afford to future 

workers the data for interesting petrologic essays, had to be passed 

over in a cursory manner. The following account can therefore be - 

little more than a sketch.

It is believed, however, that the field observations and the specimens collected will afford a basis for a brief description of the principal types of plutonic rocks and their general distribution, of a 

variety of dike rocks, and of most of the volcanic rocks occurring in 

the region. The variety of t}'pes is comprehensive enough to afford a 

basis for a general characterization of the region considered as a 

petrographic province. In many places the marginal portions of 

acidic plutonic masses exhibit interesting variations, the thorough 

investigation of which might throw light on some of the deeper petrologic problems. The observations on such occurrences are given, 

but they have generally been too imperfect to properly serve as a 

basis for anything more than mere suggestion. A few interesting 

metamorphic rocks occur which seem to deserve brief notice.
52 CASCADE RANGE NEAR FORTY-NINTH PARALLEL, [uui.ii.235.

The arrangement of the subject-matter is intended to give prominence to the more interesting facts. The metamorphic rocks will be 

disposed of first; there will then be considered, in order, the volcanic 

rocks, the plutonic rocks, and the hypabyssal rocks; finally, brief 

consideration will be given to some matters pertaining to general 

petrology.

METAMORPHIC ROCKS. 

ALTERED BASIC LAVA NEAR LOOMIS.

On the steep western wall of the valley between Loomis and Palmer 

Lake the intrusive relation of the granodiorite to the supposed Cache 

Creek volcanics is well displayed, and interesting metamorphic rocks 

have been produced by the action of the plutonic mass on the basic 

lavas.

This metamorphism is well illustrated in a specimen which lias 

megascopically the appearance of a rather fresh amygdaloidal basalt. 

It consists mainly of a fine-grained greenish black aphanitic base, in 

which are embedded roundish or somewhat irregular masses of light 

greenish gray crystalline material that appear to represent filled-in 

amygdaloidal cavities. A little calcite occurs similarly.

Examined in thin section the rock shows no trace of basaltic texture, 

yet its composition indicates that the field diagnosis was correct. The 

base is very thickly interspersed with granules of iron ore, often forming clusters. Each grain, under high magnification, appears surrounded by a little transparent crystalline material with high refractive index and double refraction, which is probably some secondary 

titaniferous mineral. The constitution of the base is somewhat 

obscured by the abundance of this iron ore, but its chief constituent 

-appears to be zoisite, recognizable by its characteristic indigo-blue 

interference color. .Considerably less abundant is ordinary green* 

hornblende. Both minerals form irregular interlocking grains, 

'thickly charged with the magnetite granules. In addition to these 

essential constituents there seems to be a little biotite, and perhaps 

also chlorite. The constitution of this base is evidently indicative 

of a basaltic composition in the original rock, for it is extremely common to find altered basalts or diabases in which the feldspar has been 

largely replaced by zoisite and the augite by hornblende.

The amygdnles, which are-perhaps the most interesting feature of 

the rock, are found to be somewhat variable in constitution. The 

largest consist mainly of a monocliiiic pyroxene, practically colorless 

in thin section, with an allotriomorphic granular structure. Mixed 

with the pyroxene are occasional individuals of deep-green hornblende 

and of very pale-green chlorite interleaved with biotite, from which 

it appears to be derived. These minerals are often developed abundantly on the border of a pyroxene amygdule. The smaller ainygdules sometimes contain some pyroxene, especially in the center, but
PETROGRAPHY. 53

consist mainly of hornblende, biotite, and chlorite. As accessories 

there occur a little calcite, some apatite in rather large grains or 

irregular, stont prisms, and a little of what appears to be siderite.

The constitution of the amygdules, as well as the complete enticement of original structures in the mass of the rock, seems to indicate 

clearly that-we have here no product of weathering or static metamorphism. The alterations seem to be explained most naturally as 

due to the intrusion of the neighboring batholithic magma.

Some other specimens collected in the same neighborhood appear 

to illustrate more advanced stages in this metaniorphism. One of 

especial interest is a fine-grained, greenish black, amphibolitic rock, 

full of irregular lenticules of greenish gray feldspathic material.

In thin section the dark portion is found to be essentially deepgreen hornblende, showing rude schistosity, together with a little 

feldspar and pale-green monoclinic pyroxene. These last are especially abundant near the boundaries of the light-colored areas, which 

are rather ill defined. They consist mainly of feldspar, near andesine, but there is a considerable proportion of the pale-green pyroxene 

already noted. The feldspar grains interlock as in a typical aplite, 

and poikilitically inclose rounded grains of pyroxene. This feldspathic material resembles the aplite of some dikes of this locality, 

to be noted in their place.

It appears strongly probable that the amphibolitic portion of this 

specimen represents metamorphosed basalt, and that the aplitic lenticules represent material introduced, perhaps by some pneumatolytic 

process, from the intrusive magma.

SCHISTS OF SKAGIT VALLEY.

Chloritic schists. Of the chloritic schists one typical specimen 

shows inegascopically a well-marked foliation modified by intense 

crumpling. The color is gray green and the-luster of the cleavage 

faces is silvery, owing to the presence of a white micaceous mineral, 

probably talc. Under the microscope the rock is found to contain, 

besides chlorite and talc, much quartz, less feldspar, and, as abundant 

accessories, apatite and an undetermined mineral. The-apatite is in 

slender prisms with very striking parallel arrangement. The other 

accessory, which forms minute, sharply developed, isometric crystals 

of greenish yellow color and high refractive index, may be a garnet. 

Another specimen of somewhat similar microscopic appearance shows 

under the microscope a quasi porphyritic structure, containing somewhat rounded grains of plagioclase in a schistose base of quartz, 

feldspar, and chlorite. The structure and composition of the rock 

rather suggest its derivation from andesite, and it may be that the 

chloritic schists of the series represent in general volcanic materials.

Glaucophane-schists. The occurrence of rocks of this interesting 

and comparatively rare group in Skagit Valley appears worthy of
54 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BUM,.286.

especial notice. The petrographic character of the glaucopliarieschists of this locality may be illustrated by descriptions of three 

specimens representing fairly distinct phases.

The first is a dense, fine-grained schist composed of nearly equal 

amounts of chlorite and glaucophane with scattered grains of epidote. 

It is cut by secondary veins of quartz, calcite, epidote, and chlorite.

The second specimen does not much resemble the first except in 

containing glaucophane, which forms prisms of moderate size scattered 

in a fine-grained schistose base composed largely of a colorless mica 

(perhaps paragonite) with some quartz and feldspar and a sprinkling 

of epidote. Standing out from this groundmass, however, are clusters 

of perfectly clear grains. In polarized light these occasionally show 

simple twinning or are marked by a single lamella. Many of the grains 

are not twinned, but all the nearly isotropic sections show in convergent light the interference figure characteristic of biaxial minerals, 

and the mineral is therefore probably all feldspar, 'though it was not 

determined specifically. The glaucophane individuals have an imperfect prismatic form, and each is bordered by a zone of epidote and 

chlorite, minerals which are also scattered through the blue amphibole.

The thin section of a third specimen shows beautiful blue crystals 

of glaucophane in a fine-grained base of quartz and chlorite. Small 

isometric crystals of garnet are thickly disseminated through, all the 

essential constituents, and magnetite occurs in a similar manner, 

though less abundantly.

In all these rocks the blue amphibole shows the optical properties 

of normal glaucophane.

It is interesting to note the sporadic occurrence of glaucophane in 

some of the ferruginous quartzites.

VOLCANIC ROCKS. 

DISTRIBUTION AND CLASSIFICATION.

As compared with their immense preponderance in the southern 

Cascades the part played by volcanic rocks in the boundary section 

of the range appears very subordinate. Yet such rocks occur in 

nearly all parts of the geologic column, and their present compara-* 

tive scarcity may be due less to any lack of volcanic activity in 

former times than 'to the immense denudation which the region has 

undergone.

Lithologically the volcanic rocks of the region vary from typical 

basalt to acidic rhyolite, these extremes being connected by a fairly 

complete chain of intermediate types. It would be useless to describe 

all, these rocks in detail. A few having especial interest will be 

treated somewhat fully, others will be characterized briefly, while 

many will be passed over with mere mention, these last including 

many old lavas so altered that they can be classified only roughly.

In order to condense the presentation of the rather scattered obser-
SMITH AND~| 

CALKINS. J

PETKOGKAPHY. 55

vations on the volcanic rocks, it lias been deemed advisable to construct the following table, in which the species are arranged in order 

of increasing basicity and their distribution and mode of occurrence 

are noted:

Species, distribution, and relations of the volcanic rocks of the region.

Species.

Soda-rhyolite ...........

Do.... .............

Rhyoli t e - p o r p h y r y , 

sheared, and altered.

phyries.

Hornblende-andesite ....

Hornblende - pyrox e n eandesite.

Pyroxene-hornblende^ 

andesite.

Hypersthene-andesite. . . 

Basaltic augite-andesite. 

Andesites, altered ......

Pyroxene -andesites, altered.

Hypers tli ene-basalt 

(with quartz).

Basalt............ ......

 basic andesite).

Locality.

South of Wenatchee . . .

North of Clover -.-..-.

Swamp Creek, Mount 

Baker district.

.....do...............

Near mouth of Siniilkameen River.

East of Hidden Lakes. .

Southwest of Wenatchee.

South of Nooksak River 

East of Hidden Lakes ..

Lower Skagit Valley, 

Sank Mountain.

(a) Just east of Hidden 

Lakes; (b) about 10 

miles east of Hidden 

Lakes.

Columbia Valley ......

Upper Skagit Valley

and Jacks Mountain.

Geologic relations.

Flow in Swauk formation, and

perhaps intrusive in same 

formation lower down.

Apparently extrusive, age unknown. 

Probably pre-Cretaceous.

Do.

Dikes in the Pasayten formation (Cretaceous) an 4 flows 

overlying.

Tertiary (?) flows overlying 

sandstones and dikes.

Flows, post-Cretaceous (?).

Intrusive (?) in Swauk (Eocene).

Flows from Mount Baker, 

probably Pleistocene.

Flows and breccia, post-Cretaceous (?).

pre-Cretaceous. 

Probably pre-Cretaceous.

(a) Apparently small stock 'or 

dike in post-Cretaceous (?) 

andesites; (6) dike in granite.

Yakima Miocene.

Flows and breccias in Cache

Creek (?), Carboniferous. 

Flows and breccias interbedded with pre-Cretaceous sediments (Cache Creek?).

BHYOL1TES.

Soda-rhyoliie near Wenatchee. The general hues of these rocks are 

very light, varying from gray or pale lilac to nearly white. In hand 

specimens the main portion is seen to consist of a laminated, usually 

lithoklal, groundmass, carrying rather numerous small phenocrysts 

of quartz and feldspar and a few inconspicuous tablets of biotite.
56 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BULL.235.

On examination of the thin section one is struck at once by the 

extreme corrosion shown by both -quartz and feldspars. The quartz 

phenocrysts are rounded and embayed, while those of feldspar show 

very irregular outlines and abundant glass inclusions.

The feldspar, phenocrysts, which in the absence of chemical analysis afford the best available indication as to the composition of a 

rhyolite, seem to be all plagioclase. Different species are represented, 

a few crystals showing marked zonal structure and having rather 

basic cores, while others are practically homogeneous and generally 

characterized by very fine and sharp twin lamellae. Some of these 

latter in sections perpendicular to the negative bisectrix were determined as albite. The character of the phenocrysts thus seems to indicate that these rocks belong to the group of soda-rhyelites.

Soda-rhyolite near Clover. The rock of this locality appears to be 

allied in composition to the one just described. It is more crystalline, 

showing, megascopically, abundant and rather large phenocrysts of 

quartz and dull-pink feldspar, with some biotite, in an aphanitic gray 

groundniass. Under, the microscope it appears that the feldspar 

phenocrysts are much altered, many being almost completely replaced 

by calcite, while others are clouded with kaolin. Most of the determinable feldspars are striated; some were identified as albite, though 

the abundance of calcite would indicate the original presence of a 

more basic species. There are a few small phenocrysts of orthoclase, but it appears probable that soda is the dominant alkali in this 

rock as in that near Wenatchee. It may be that the orthoclase phenocrysts belong to, a later stage of crystallization than was reached in 

the Wenatchee rock and therefore do not indicate any marked difference in chemical composition.

. ANDBSITES.

Daciie. This rock shows; megascopically, abundant phenocrysts 

of plagioclase, with fewer of quartz and of ferromagnesian constituents, in an aphanitic groundniass of light-gray or drab hue. By 

the aid of the microscope the plagioclase phenocrysts are determined 

as andesine-oligoclase with some oligoclase. Biotite is found porphyritically developed in all the specimens, and all contain pseudornorphs after another ferromagnesian mineral of prismatic form, 

presumably hornblende. The groundmasses are holocrystalline and 

consist essentially of plagioclase, quartz, and orthoclase; in texture 

they are sometimes microgranular, sometimes micropoikilitic.

Hornblende-pyroxene-andesite. This rock, seen along the eastern 

border of the Hidden Lakes volcanic area, has phenocrysts of labradorite, brownish-green hornblende, augite, and hypersthene, in order 

of abundance. The groundmass contains plagioclase microlites and 

allotrioinorphic microscopic grains supposed to be quartz and orthoclase. Magnetite also abounds in the groundniass and forms heavy 

borders about the hornblende phenocrysts.
SMITH AND") T>TJ"TT>nm? A13TTV ^7 CALKINS. J PElKOGUAPJiY. O<

The hornblende-pyroxene-andesite, developed south of Wenatchee, 

is mostly much weathered, but some exceptionally fresh material was 

collected from the bold western face, which is worthy of description. 

Macroscopically it is seen that the greater part of the rock is constituted by a light olive-green, glassy groundmass of resinous luster, 

while there are abundant phenocrysts of glassy striated feldspar and 

of prismatic dark ferromagnesian minerals. By microscopic study of 

the thin section it is found that the phenocrysts are plagioclase, 

hypersthene, hornblende, augite, and magnetite, while the groundmass 

is of the hyalopilitic type, consisting of microlites of plagioclase and 

hypersthene, with grains of magnetite, in a clear glassy base.

The phenocrystic plagioclase is strikingly characterized by evidences of corrosion and by very pronounced zonal structure. The 

most abundant species entering into the constitution of the zonallybuilt crystals is sodic labradorite (AfyAuj), but other species more 

basic and much more acidic occur. Many of the crystals have curved 

outlines, evidently resulting from resorption, and nearly all are more 

or less honeycombed with glass inclusions. In some cases the entire 

crystal is a mere sponge or skeleton, while in others there is a broad 

zone of irregular glass inclusions, frequently surrounded by a rim of 

clear feldspar.

The feldspar microlites of the groundmass show extinction angles 

that indicate a composition slightly more acidic than A^An^

Of the ferroinaguesian constituents the most abundant is strongly 

pleochroic hypersthene, occurring in well-formed elongated prisms. 

Next in order of abundance is a hornblende, of deep brownish green 

tint; which in part shows dusty borders containing magnetite and 

some indeterminate substance. Green augite, in rather stout, imperfectly developed prisms, is rather subordinate in amount. Parallel 

intergrowths of hornblende with hypersthene and of hypersthene 

with augite were noted.

An interesting segregation was observed, consisting of a granular 

aggregate of plagioclase and hornblende of the same character as 

that occurring porphyritically.

Pyroxene-andesite of Mount Baker. It appears worth while to 

describe in some detail a nearly holocrystalline specimen wh ich probably best expresses the composition of the lava.

This rock, which was observed at Austin Pass, has a distinct lamellar 

parting. Megascopic examination of the hand specimen shows rather 

abuWlant phenocrysts of striated feldspar and dark-green pyroxene 

in <a light-gray, fine-grained, but evidently crystalline groundmass, 

with rather silky luster.

Under the microscope the constituents of the rock are found to be 

plagioclase, augite, hypersthene, iron ore, apatite, and a rather "small 

amount of glass. All the minerals are perfectly fresh.

The texture is fluxional and porphyritic, but is peculiar in that the 

feldspar occurs in three generations. At the first preliminary exam-
58 CASCADE RANGE. NEAR FORTY-NINTH PARALLEL. [BULL. 235.

ination of the thin section through low-power lenses, the writer was 

struck by the fact that the feldspars were divisible on the basis of 

size into three classes. Speaking generally, the first class consists of 

those crystals which are easily recognized as plagioclase in the hand 

specimen by the unaided eye; the second, of those that produce the 

reflections that give the groundmass its sparkling crystalline appearance; the third, of those of purely microscopic dimensions. Attempts 

to determine the average size of the crystals of each class led to the 

perception of the fact that the divisions are not absolutely sharp, and 

that the intervals between them may be bridged over by graded series; 

nevertheless, the number of doubtful or intermediate individuals is 

very subordinate to that of the feldspars readily assignable to a particular generation. Estimates based on actual measurements give 

the average length for the crystals of each class as follows: For the 

large phenocrysts, from 2 to 3 millimeters; for the large crystals of 

the grouudmass, about 0.2 millimeter; for the microlites of the last 

generation, about 0.06 millimeter. The largest part of the feldspar 

belongs to the second division.

The pyroxene crystals are not so definitely classifiable with regard 

to size as the feldspars. The greater portion is in crystals intermediate in magnitude between the first and second generations of feldspar, the maximum dimensions for the pyroxene being less than for 

the feldspar phenocrysts. Grains and prisms of pyroxene with microlitic dimensions are also abundant.

The magnetite occurs in two generations, the first being represented 

by rather sparsely distributed grains of about 0.15 millimeter in 

average diameter, very frequently in association with the pyroxenes.

The study of the optical properties of the feldspar shows the larger 

crystals to be built up zonally, with cores having a composition near 

Ab3 An4 , and shells that show an oscillation of composition during 

growth, but are in general more acidic than the kernel. The crystals 

of the second generation are very similar to those of the first, and are 

but little, if any, less basic in average composition. The microlitic 

feldspar gives extinction angles of about 25° in the " square sections " 

nearly normal to the edge 001:010, and is therefore slightly more sodic 

than Abt Aiij. The larger phenocrysts are often in part honeycombed 

with irregular inclusions of brown glass that tell the story of corrosion that has taken place at certain periods of their growth.

The pyroxenes comprise augite and hypersthene, with the latter 

apparently in slight excess. The rhombic species has fairly strong 

pleochroism in green and reddish brown tints, while augite is in thin 

section pal6 green and not sensibly pleochroic. The glassy residue 

is brown and contains crystallitic bodies of undetermined nature, 

comprising the globulitic and longulitic forms.

The foot of the flow that reaches the Nooksak shows a characteristic columnar structure. As regards the petrographic character of the
PETBOGKAPHY. 59

rock collected here, brief description will suffice to indicate its differences from the rock described above.

The inineralogic constitution of the two is essentially the same, 

but the vitreous character of the black aphanitic groundmass of the 

second specimen is evident megascopically. Under the microscope 

the threefold classification of the feldspar crystals becomes apparent, 

though less striking than in the case of the more crystalline rock, 

since the second generation is but sparingly represented.

The feldspar phenocrysts are somewhat less basic than in the first 

specimen; the kernels give no extinction angles higher than 27°, 

which would indicate their composition to be near Abj An1? while the 

outer zones are in general even more acidic. In addition to augite and 

hypersthene there is an occasional corroded individual of brownish 

green hornblende with a rim of magnetite. The groundmass shows 

the typical hyalopilitic texture, being composed of brown glass filled 

with microlites of feldspar and pyroxene and grains of magnetite.

The lavas of Mount Rainier have been described by the senior 

author," and it is noteworthy that the type most abundantly represented on Rainier is essentially similar to the Mount Baker lava that 

has just been described.

Basaltic augite-andesite. The rocks along the canyon north of the 

Hidden Lakes seem to occupy a position in the classification scheme 

about on the line between andesite and basalt. Megascopically they 

appear dark colored and conspicuously porphyritic. The most prominent phenocrysts are large plagioclases, and there are also numerous 

much smaller phenocrysts of augite. In thin section it is found that 

the plagioclase phenocrysts are too much altered for specific determination. The fine-grained groundmass contains both plagioclase and 

augite in a second generation, together with magnetite and perhaps 

originally hypersthene, and some glass. The plagioclase of the 

groundmass is in sharply developed laths, and the pyroxene, having 

less perfect crystallographic development and often showing a tendency to inclose the feldspar, is plainly posterior to it. The texture 

is therefore intersertal and emphasizes the relation of the rock to 

basalt. The prisms of augite of ten have a sort of central "rib "of 

olive-green material, which resembles the common alteration product 

of hypersthene, and indicates that there was originally some rhombic 

pyroxene intergrown with the augite on the usual plan. The plagioclase microlites were determined in some cases as labradorites of the 

composition Afy Aux .

There is considerable secondary material, of which the most interesting is a yellowish green substance resembling serpentine. The 

mineral forms irregular patches in the groundmass, and oblong or 

somewhat rounded areas about as large as the augite phenocrysts. It

"Smith, GK O., Rocks of Mount Rainier: Eighteentli Ann. Rept. U. S. Geol. Survey, pt. 2, pp. 

41G-432.
60 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BULL. 235.

is supposed to represent either hyperstliene or olivine, more probably 

the former.

Pyroxene-andesites of Skagit Valley and Sank Mountain. The 

great body of old volcanic rocks from which Sank Mountain is carved 

is too much altered for very satisfactory study. Their porphyritic 

texture has been observed, however, and their basic- composition 

is evident from the abundance of such secondary minerals as chlorite, 

calcite, epidote, and leucoxene. The feldspars are mostly replaced 

by saussuritic material, but some still show albite twinning. Remnants of augite phenocrysts are still present. Hypersthene is not 

represented by any recognizable pseudomorphs, but, in view of its 

susceptibility to weathering, it may nevertheless have been present. 

The andesites of this locality appear to have belonged to ordinary 

pyroxene-andesite or to an augite-andesite approaching basalt, both 

of which types have important development in the great Tertiary 

accumulations of volcanic rocks farther south.

BASALTS.

Hyperstliene-basalt. The hypersthene-basalt was observed to form 

a small knob overlooking the smallest of the Hidden Lakes. In the 

hand specimen large phenocrysts of olivine are conspicuous, rather 

sparingly distributed in a dense black aphanitic groundmass. Under 

the microscope this groundmass is found to be hyalopilitic, consisting 

of plagioclase, augite, hyperstliene, and magnetite, with considerable 

glass. The rhombic pyroxene also forms phenocrysts, which are, however, much smaller than those of olivine. ' There are a few patches of 

brown glass with stout prisms of augite embedded in them, which are 

altogether similar to the features produced in quartz basalts by the 

complete resorption of the quartz grains. There is little doubt, therefore, that quartz has been present in the rock.

Comparable with this rock is the material forming certain dikes in 

the granite about 10 miles east of Hidden Lakes. Here, however, 

'augite forms large'phenocrysts, and olivine appears to be lacking. The 

thin section contains a grain of highly corroded quartz surrounded by 

a zone of calcite and a material like iddingsite, which appear to replace 

glass, both forming irregular areas in the groundmass.

Yakima basalt. This formation has been made the subject of 

detailed description in other publications," and only its leading characteristics need be noticed here.

The petrographic character of the rocks is remarkably constant. 

They seem, to be almost without exception normal basalts, composed 

essentially of labradorite, augite, olivine, and iron ore (usually titaniferous magnetite); the order given being, in general, that of relative

«Smith, G. O., Description of Mount Stuart quadrangle: Geologic Atlas U. S., folio 106, U. S. 

Geol. Survey, 1904; Smith, G. O., Description of Bllensburg quadrangle: Geologic Atlas U. S., 

folio86, U. S. Geol. Survey, 1903; Calkins, F. C., Bull. Geol. Dept. Univ. of California, vol.13, No. 5, 

1902, pp. 159-165.
8o"I,"-«- D "l PETROGRAPHY. 61

abundance. Apatite is the only constant accessory. As regards 

degree of crystallinity, the lavas vary from nearly pure glass to holocrystalline dolerites, crystalline matter nearly always predominating 

markedly over glass. The basalts are rarely notably porphyritic, the 

common textures being intersertal for the hypocrystalline and ophitic 

for the holocrystalline phases.

Metabasalts. The basaltic rocks of the old formations of Okanogan 

Valley and the region just east of Skagit River are represented only 

by specimens of extremely altered rock, which it would be unprofitable to describe in detail. Generally there is little or none of the original material left, and the basaltic character of the rocks is inferred 

from the nature of the secondary compounds or from traces of the 

original textures. It is quite possible, however, that these volcanic 

masses may include some basic pyroxene-andesites.

PLUTONIC ROCKS.

DISTRIBUTION AND CLASSIFICATION.

The vast development of pin tonic rocks in the Northern Cascades 

has been shown in the preceding chapter, and in view of their geologic importance their petrographic character must have greater general interest than that of any other cjass of rocks. The description of 

the various species may, therefore, it seems, be conveniently preceded 

by a table, arranged in order of increasing basicity, showing their areal 

distribution. Such an arrangement will help to bring out the close 

petrographic relationship between the different types, and the descriptions which follow will have the emphasizing of these relationships 

for their most important object.

Species and distribution of the plutonic rocks of tlie region.

Species. Occurrence.

Biotite-inuscovite-granite.

Biotite-granite

Acidic granocliorite. 

Basic granocliorite..

Quartz-raica-diorite

Batholiths near mouth of Okanogan Valley and 

in central and western parts of Okanogan 

Mountains.

Batholiths, probably post-Carboniferous, Okano- 

.gan Valley and Okanogan Mountains.

Batholiths in western part of Skagit Mountains.

Batholiths, probably post-Carboniferous. Valley of Columbia River, in eastern portion of. 

Okanogan Mountains, Skagit Valley, and Skagit Mountains. Marginal phase of acidic granodiorite in Skagit Mountains and of biotitegranite in Okanogan Mountains.

Batholiths in Okanogan Valley and in Pasayten 

formation (Cretaceous) of Hozpuieen Range. 

Marginal phase of acidic granocliorite in Skagit 

Mountains and of biotite-granite in Okanogan 

Valley. Minor intrusions in Cache Creek 

rocks northeast of Loomis.
62 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [miu,.233. 

Species and distribution of the plutonic rocks Continued.

Species. Occurrence.

Quartz-pyroxene-mica-diorite.. 

Hornblende-diorite.............

Quartz - bearing augite - inicadiorite.

Gabbro (uralitic) ...... J.....'.

Olivine-hornblende-gabbro ... 

Saxonite .......................

Peridot! tes and pyroxenites, alteredSmall mass at east end of Horseshoe.

Marginal phase of acidic granodiorite. western 

Skagit Mountains.

Do.

Abyssal representative of flows in Cache Creek 

group, Okanogan Valley, and intrusive (?) in 

serpentine, Mount Chopaka.

Marginal phase of acidic granodiorite, western 

Skagit Mountains.

Batholith in pre-Cretaceous rocks, Ruby Creek, 

Hozomeen Range.

Batholithic masses, Mount Chopaka.

In relative importance the rocks tabulated above vary widety. The 

most extensively developed class of rocks are probably the granodiorites. The granites, taken together, are little inferior in extent to 

the granodiorites; of the two types the biotite-granites are probably 

the more abundant. The quartz-diorites apparent^ come next, while 

diorite without essential quartz is very scarce. The gabbros and 

ultrabasic rocks have relatively slight volume. The most striking 

general fact is the preponderance of acidic over basic plutonic rocks.

GRANITES.

Biotite-muscovite-granite of Moiint Remmel type. The granite from 

the central belt, in which Mount Kemmel lies, is apparently the most 

acidic plutonic rock with which we have to deal. As seen in the field 

on weathered surfaces it appears almost white. This, however, is 

not the color of the freshest material, which is rather brownish, owing 

to the smoky tint of the quartz and the flesh color of part of the feldspar. Biotite and muscovite are essential, but both together constitute but a very small part of the rock. A gneissic banding evident 

on broad exposures, though not sufficiently distinct to appear in hand 

specimens, is developed in portions of the mass. This structure was 

observed on the slopes of Mount Rernmel, but the rock forming the 

ridge across the canyon to the west, while otherwise similar, is not 

foliated. An interesting feature is the local occurrence of small red 

garnets. The texture is evenly granular and the grain rather fine.

The essential mineralogic composition of a specimen from. Mount 

Remmel, as determined by microscopic study, is roughly indicated by 

the expression quartz > orthoclase > oligoclase > biotite-muscovite. 

In addition to small amounts of magnetite, zircon, and apatite, garnet 

occurs in well-formed rhombic dodecahedra about one-half millimeter
SMITH ANU 

CALKINSs u ] PETROGRAPHY. 63

in average diameter. Some evidence of pressure and shearing is 

afforded by undulatory extinction in the quartz and a tendency to 

linear arrangement of the mica. 

A specimen from farther north in the same belt of granite, though, 

very similar in megascopic appearance to the rock just described, is 

free from garnet and appears to have more plagioclase than orthoclase. Whether or not this soda-rich phase is merely local, and what 

is the proportion of the alkalies in the magma as a whole, we are not 

prepared to say, though we should rather expect to find potash feldspar predominant. It does not seem probable, however, that there is, 

on the whole, decided predominance of potash feldspar over soda-lime 

feldspar.

. Clcissificatory position.- The question will present itself at once to 

many petrographers Avhether or not it is proper to call this rock a 

granite, for it evidently has a close relationship with the adamellites 

of Brogger. Several considerations, however, have induced us provisionally to designate this and other related types soon to be described 

granites.

The term adamellite, it may be remarked in passing, is open to some 

objection on theoretical grounds. It is evident, for example, that if 

in the Mount Remmel rock a considerable part of the soda in the 

oligoclase were combined with potash in soda orthoclase, or went into 

albite intergrown with, orthoclase, the rock, though not changed in 

chemical composition, would be called a granite. The objection to 

the name on this ground is of course common to all terminology based 

on mineralogic composition, and is one of the strong arguments for 

basing the classification of rocks primarily on chemical composition. 

Without chemical analysis, however, we are unable to classify our 

rocks according to a chemical scheme.

But the principal reason for using the term granite here consists in 

the approximate character of our data in regard to the quantitative 

relations of the feldspars. Optical estimation of the mineral constitution of coarse-grained porphyritic rocks is attended with difficulty 

and uncertainty, and it did not seem justifiable, in view of the preliminary nature of this report and the scarcity of the material in hand, 

to have chemical analyses made. Since the use of the term adamellite would seem to imply a more exact knowledge of the constitution 

of the rock than we really have, it has seemed best to use the more 

familiar and possibly less definite term "granite."

It is desired, however, to call attention emphatically to the fact 

more important than the question of terminology that the most acidic 

plutonic rocks of the Northern Cascades are comparatively rich in 

oligoclase, and thus richer in soda than the typical granites.

Biotite-muscomte-granite of Okanogan Valley type. A rock closely 

related to the Mount Remmel type, but perhaps a little less siliceous, 

is represented by handsome fresh material collected a few miles west 

of the mouth of Okanogan River.
64 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [HULL.235.

The general line is light gray. The feldspars, taken together, constitute more than half of the rock, and quartz, often in large, irregular anhedra, is very abundant. Biotite in small flakes is present in 

small amount, and many yellowish brown crystals of titanite are 

rather noticeable megascopically. A little muscovite is present, but 

it is quite inconspicuous. The most interesting feature of the rock 

is the potash feldspar, which mostly occurs in phenocrysts measuring 

usually between 2.5 centimeters and 0.8 centimeter in diameter. The 

large phenocrysts have well-defined crystal boundaries, but have 

fairly numerous inclusions consisting of small feldspar grains and 

biotite, while 'quartz often penetrates the borders. Other smaller 

areas of the potash feldspar, however, are more irregular, some 

appearing as mere allotriomorphic plates poikilitically inclosing grains 

of the other constituents.

Microscopic examination shows the plagioclase to be oligoclase with 

faintly defined zonal structure. The potash feldspar, which shows 

in large part the twin structure of microcline, incloses oligoclase, 

biotite, and sometimes quartz and micropegmatite. Zircon, apatite, 

and magnetite occur as accessories in addition to titanite. The quantitative relation between potash feldspar and plagioclase can hardly 

be satisfactorily determined without chemical analysis; megascopicalty the alkali feldspar, and microscopically the plagioclase, appears 

the more prominent, and they are probably not far from .equal in 

amount. The remarks on the classification of the Mount Remmel 

type of granite have their application here.

The gneiss forming the last peak passed in our westward course 

across the Okanogan granite belt appears mineralogically very similar 

to the rock from Okanogau Valley. The feldspars are partly pink and 

partly white and glassy. The quartz, which is abundant, has a 

noticeable and peculiar greasy luster, due to its microstructure, 

which will presently be described. The essential minerals and their 

rough quantitative relations in. the one thin section examined are: 

Oligoclase > quartz > orthoclase > biotite > muscovite. Only the 

usual accessories, magnetite, apatite, and zircon, were noted.

The textural modification produced by pressure and shearing 

deserves brief notice. Megascopically the rock shows a distinctly 

banded appearance, but under the microscope it exhibits some more 

unusual phenomena. The micas exhibit the usual disposition in 

wavy lines, and the feldspar crystals have suffered some crushing. 

The quartz, however, shows the most interesting cataclastic structure. 

The original anhedra have been crushed to fine mosaics of elongated, 

lenticular, irregularly bounded grains, each exhibiting marked undulatory extinction. These folia of quartz have a parallel arrangement 

and show a fluidal disposition'about the larger grains of feldspar. 

The appearance of this structure in polarized light is intrinsically 

beautiful and most clearly expressive of the intense dynamic stresses 

which the rock has undergone.
PETROGRAPHY. 65

Biotiie-granite. The biotite-granites developed so extensively in 

the Okanogan Mountains and the adjacent portion of Okanogan 

Valley have a clear relation to the type just described, and mostly 

resemble it closely in mineralogic and textnral .characters. These 

rocks vary somewhat among themselves, yet not so markedly but that 

our present purpose may be served best by describing them together.

The biotite-granites are in general characterized megascopically by 

rather abundant quartz and orthoclase, the last mineral being very 

commonly but not always conspicuous for its porphyritic deArelopinent. The biotite is not generally abundant, and the hornblende 

and muscovite which occur locally are perhaps not to be considered 

as essential. Microscopically, small quantities of magnetite, apatite, 

and zircon are observed, while titanite is usually a rather abundant 

accessory.

The accessories and the micas and hornblende present no features

that entitle them to especial notice in this brief description. The 

quartz occurs commonly in rather large masses, which are found on 

microscopic study to be granular aggregates. The mineral is often 

very conspicuous megascopically, especially where, as is frequently the 

case, it has a smoky tint, contrasting Avith the white or pink of the 

feldspars. The feldspars are the most interesting minerals of these 

rocks, and of these, while orthoclase is rather the most prominent 

megascopically, plagioclase is found on microscopic study to be almost 

equally important.

The interesting porphyritic development frequently shown by the 

orthoclase is strikingly illustrated in the area near the foot of Lake 

Osoyoos and on the north side of the Horseshoe, where Avell-formed 

crystals may be picked up in any quantity from the sand that arises 

from the surface disintegration of the rock. In thin section these 

phenocrysts are found to inclose rather numerous individuals of plagioclase, green hornblende, and quartz, in order of abundance, all of 

which show good crystal form except the quartz. The inclusions, 

which are evenly distributed, generally show no definite crystallographic relation to their host, except that a considerable proportion 

of the plagioclase crystals appears to have approximately the orienta-- 

tion expressed as follows: a of plagioclase parallel to a of orthoclase, 

and c of plagioclase parallel to b of orthoclase.

These phenocrysts often show perthitic veining, and microcline 

twinning may be developed in a portion of the crystal. In addition 

to the phenocrystic alkali feldspar there is generally some microcline 

forming a poikilitic cement for the other constituents of the groundmass in which the phenocrysts are embedded. Where the potash 

feldspar is not porphyritic it is generally microcline and allotriornorphic toward all other minerals, even quartz inclosed in it sometimes 

showing sharp crystal form.

The plagioclase generally shows good crystal form. It is always

Bull. 235 04 5
66 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BULL.235.

slightly zoned,' but nearly all belongs to acidic oligoclase. It commonly shows much greater susceptibility to weathering'than the orthoclase, a fact strikingly illustrated in the rock from near Mie foot of 

Lake Osoyoos, where, although the potash feldspar is almost fresh, 

the plaglioclase is thoroughly clouded with mica, kaolin, quartz, calcite, and epidote.

The proportion between the feldspars in these rocks deserves especial comment. The plagioclase, not very conspicuous megascopically, 

is found by microscopic study to be of the same order of importance as 

the potash feldspar. Exact optical estimates in regard to the relative 

proportions between the two classes are made difficult by the coarse 

grain and porphyritic textures. While merely megascopic examination would probably lead to an overestimate of the potash feldspar,, 

the phenocrysts are rather more .apt to be lost in grinding thaii the 

groundmass, in which plagioclase predominates, so that estimates 

based solely on microscopic evidence, would lead to error in the opposite direction. Taking everything into consideration, it appears probable that on the whole the granites of this region contain more potash 

feldspar than plagioclase, but that the predominance of the potash 

feldspar is not very decided.

From the main type, constituting the larger areas, there are local 

variations. A specimen taken near the boundary north of Loornis 

differs from the ordinary porphyritic phase in having a slightly larger 

proportion of dark minerals, including some hornblende as well as 

biotite. Farther south toward Loomis the approach to the border of 

the mass seems to be attended by an increase in the basicity of the 

intrusive rock, and the principal zone contains types that, falling 

under granodiorite. and quartz-diorite, will be described further on.

GRANOD1ORITES.

Acidic granodiorite of Mount Baker district. In megascopic aspect

the plutonic rock, so important about the headwaters of Silica Creek, 

resembles the biotite-granites just described, in so far as it contains 

abundant quartz, a rather small amount of biotite as the characteristic ferromagnesian constituent, and feldspar constituting more than, 

half the rock. Close examination shows, however, that most of the 

feldspar is striated, a fact that distinguishes this rock clearly in classificatory position from the true granites.

In large masses the rock shows a light pure-gray color, caused by 

the combined effect of the dominant pure-white feldspar and colorless 

quartz 'with a rather small amount of biotite and a very little hornblende. The orthoclase may be seen on close examination showing the 

characteristic allotriomorphic relation toward the other constituents.

Careful study of the thin sections shows that the rough qualitative 

relations of the essential constituents may be indicated by the expression: Plagioclase > quartz> orthoclase and inicrocline> biotite^ 

hornblende. The last-named mineral is found in so small amount
SMITH AND 

CALKINS D ] PETROGRAPHY. 67

that it should perhaps be ranked as an accessory, together with a very 

little muscovite and ordinary amounts of magnetite, apatite, and 

titanite.

The plagioclase is generally idioinorphic and strongly zoned, the 

cores of the crystals usually belonging to andesine, while the more 

acidic shells are of oligoclase. The quartz occurs in the usual manner, 

forming coarse irregular aggregates, allotriomorphic against plagioclase and biotite. This mica is of the common greenish brown variety. 

The orthoclase has the usual structural relationships, occurring in 

fairly large spongiform individuals, allotriomorphic toward all the 

other constituents but quartz. Intergrowths of orthoclase and quartz 

are found, in some of which, contrary to the usual quantitative and 

 structural relations, the feldspar is subordinate and makes cuneiform 

figures in the quartz. The general order of crystallization for the 

essential constituents is: Plagioclase, biotite, quartz and potash feldspar (nearly contemporaneous).

As regards classification this rock clearly falls within the group of 

granodiorites, which are defined by Lindgren as 

A member of the great family of rocks with predominating soda-lime feldspars, 

distinguished by a granular texture, grayish color, and a mineral composition of 

quartz, oligoclase or andesine, orthoclase or microcline, hornblende or biotite 

(usually both), the accessories being titanite, apatite, magnetite, and zircon/'

The small amount of dark minerals, however, and the high percentage of quartz rather noteworthy in view of the predominance and 

moderately basic character of the plagioclase place the rock well 

toward the acidic end of the granodiorite group. On the other hand, 

the character of the feldspars very clearly separates it from the granites or the quartz-inonzonites.

The basic rocks which have already been noted as occurring in the 

marginal portion of this mass include granodiorite of a more basic 

type, diorite, and gabbro, which will be described in their places. 

The origin of the marginal variations will also be discussed later.

Basic type of granodiorite, The extensive masses of granodiorite 

found along Columbia River, in the Okanogan Mountains, and in 

Skagit Valley are of a type more basic than the rock of 'the Mount 

Baker district, from which it differs in containing as much hornblende 

as biotite and a considerably smaller though still essential proportion 

of quartz, while orthoclase plays a still more subordinate role than in 

the rock last described. ;

The typical material is a gray rock of moderately coarse-granular 

texture. The feldspars, which constitute together about half the 

rock, are generally pure white, though in exceptional cases where 

they are clear and glassy they appear gray, giving the rock a darker

» Lindgren, W., Ani. Jour. Sci., 4th series, vol. 9,1900, p. 281. In the article referred to, Doctor 

Lindgren has discussed thoroughly the limits of this group and its relation to neighboring 

types. As he points out, the granodiorites form a well-defined natural group, which is extensively developod in the Sierra Nevada, and which has perhaps received insufficient recognition 

from European petrographers.
68 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BULL.235.

tone. The outlines of the striated feldspar are idiomorphie, but the 

orthoclase when recognizable is always in the form of a cement for 

the other constituents. By observation of the basal reflections it 

often may be seen to form irregular plates often 1 square centimeter 

or more in area, thickly interspersed with crystals of plagioclase and 

the dark minerals. The quartz, which is colorless, occurs in irregular grains. The hornblende always shows a tendency to prismatic 

form, and occasionaly builds well-developed crystals with a maximum length of about 1 centimeter. The biotite forms tablets that are 

sometimes hexagonal, but oftener of irregular outline.

Microscopic examination shows the presence as accessories of considerable magnetite, apatite, and titanite, and of a little zircon.

The relative amounts of the essential minerals are indicated by the 

expression: Plagioclase > quartz > hornblende > < biotite > orthoclase.

The plagioclase almost always shows some zonal banding, which, 

however, is not generally very distinct. Usually the central and larger 

portion of each crystal is andesine, while the peripheral portion is 

oligoclase. The hornblende and biotite are of the most common varieties, the amphibole being deep green and pleochroic, and the mica 

a deep greenish brown lepidomelane with an interference figure that 

is clearly biaxial, but in which the hyperbolic brushes do not separate 

in a complete revolution of the stage.

The general order of crystallization seems to be as follows: Apatite, 

titanite, zircon and magnetite, plagioclase, hornblende and biotite, 

quartz and orthoclase. It is interesting, however, to note that innumerable exceptions to this general order occur in every slide. Each one 

of the essentials has been found to inclose all the other minerals 

excepting orthoclase; in a few cases large irregular grains of iron ore 

inclose plagioclase and quartz. The hornblende 0 and biotite sometimes show the poikilitic structure developed to an extreme degree.

Basic segregations occur in the granodiorite, which mineralogically 

differ from the normal rock in containing a larger proportion of the 

ferromagnesian constituents, among which hornblende is usually 

dominant. Of the light-colored minerals, quartz becomes very subordinate, while the orthoclase increases relatively and sometimes 

equals or exceeds the plagioclase, which is generally andesine as in 

the normal granodiorite.

Such a rock forms blotches in the normal granodiorite west of the 

Horseshoe, just described. The rock consists of irregular interlocking sponge-like individuals of orthoclase, often an inch or more in 

diameter, filled with inclusions of the other constituents. These in 

the aggregate exceed the cementing feldspar, and the presence of the 

latter is recognized macroscopically only by observation of the mottled 

reflections from cleavage faces.

The thin section cut from this rock shows a single crystal plate of 

orthoclase, in which are interspersed, without any regularity of
8c i»s.D ] PETROGRAPHY. 69

orientation, plagioclase, hornblende, biotite, quartz, and augite, 

besides the usual accessories.

DIORITKS.

Quartz-mica-diorites. The rocks of this spe'eies show a most markedly close relationship with the more basic granodiorites, the mineral 

constituents and their structural relations to one another being the 

same as in the granodiorites. It will not be necessary, therefore, to 

describe them very fully. The difference between the two classes of 

.rocks lies in the quantitative relations of the constituents, the quartzdiorites being distinguished by having a large'proportion of ferromagnesian. minerals, with quartz and orthoclase distinctly subordinate and 

not readily seen megascopically. The accessories are the same as 

in the granodiorite, but magnetite and apatite are more abundant, 

titanite rather less so, and zircon scarce. The plagioclase is, as would 

be expected, rather more basic than in the granodiorites. The crystals are strongly zoned, with oligoclase, andesine, and labraclorite 

entering into their constitution. Usually the average composition is 

not far from Ab4 An3 .

Such are the general characteristics of the quartz-mica-diorites of 

this region. There is, however, some variation within the group. On 

the side closer to granodiorite lie the gneissic quartz-diorite of Clover 

and a rock from the marginal zone of the biotite-granite north of 

Loo in is. The latter rock, being even grained and of moderately 

fine texture, is well fitted for analysis by direct optical measurement of the constituents in thin section, according to the method of 

Rosiwal."

The results obtained by this method, the average composition of 

the plagioclase being estimated as Ab4 An3 , are as follows:

Mineralogic composition of quartz-diorite north of Loomis.

Quartz ................................................ 11.8

Orthoclase............................................. 4.9

Albite................................................. 31.4

Anorthite -..-...-.-........--...-.. - .........-... ..... 16.7

Biotite ...._-._-.-.--.-.------.-..-----.--..-.--..-.. 16.8

Hornblende............................................ 15.6

Augite-.-.---....--.. --....-- -----.-.-...--......-. .6

Magnetite............................................. 1.9

Apatite................................................. .3

Total.....-..............:....................... 100.0

In addition to the constituents measured there is a small amount of 

titanite. The order of crystallization is in general the following: 

Accessories; plagioclase; augite, hornblende, and biotite; orthoclase 

and quartz.

The quartz-diorite of Ruby Creek is apparently somewhat more

aRosiwal, A., Verhand. d. K. -k. geol. Reichsanstalt, 1898, pp. 148-175.
70 CASCADE RANGE NEAR FORTY-NINTH PARALLEL, [BULL. 236.

basic. The quantitative relation of the essential constituents is: Plagioclase > hornblende > quartz > orthoclase > biotite; magnetite 

and apatite are rather abundant accessories, and some titan.ite occurs. 

The plagioclase is in idiomorphic strongly zoned crystals whose kernels are often as basic as Abt Ant , but whose outer shells belong to 

andesine and oligoclase. The order of crystallization of the essentials 

is'very clear. The plagioclase is always in well-developed crystals.

The horn blende forms prisms which are sharply idiomorphic against 

quartz and orthoclase, but are xenomorphic against the the plagioclase. 

The biotite, which is represented by pseudomorphs of chlorite, exhibits 

the same relations toward the respective light-colored minerals as 

does the hornblende. The quartz and orthoclase are in characteristic anhedra.

, Quartz-pyroxene-mica-diorite. This rock is found in a rather small 

mass at the east end of the Horseshoe. Megascopically it appears as 

a dark greenish gray, evenly granular rock of rather fine texture. 

Under the microscope its constituent minerals are found to be plagioclase, hypersthene, angite, hornblende, biotite, quartz, orthoclase, 

with accessory apatite, zircon, and iron ore. The accessories are all 

relatively abundant, zircon occurring in unusually large crystals. 

The plagioclase is in zonally built crystals, the kernels usually being 

approximately of the composition Ab, An t and the rims belonging to 

oligoclase. The quartz and orthoclase are subordinate in quantity 

and fill.the anhedral spaces between the other constituents.

Especially interesting is the mode of occurrence of the ferromagnesian minerals, which are generally intergrown with one another. The 

most common intergrowths are of either pyroxene with the hornblende, but not infrequently all four minerals are found in parallel 

intergrowth, the order of succession from center to periphery being: 

Hypersthene, augite, hornblende, and biotite.

The rock is similar to some of the Electric Peak diorites, and the 

intergrowths of the ferromagnesian minerals are identical in character with those so well described and figured in Professor Iddings's 

classic memoir on the petrography of Electric Peak and Sepulchre 

Mountain^

Quartz-augile-mica-diorite. This rock, found in the peripheral zone 

of the granodiorite at Mamie Pass, is a rock well toward the basic 

end of the quartz-diorite group.

Megascopically it appears as of moderately coarse grain and of 

dark-gray color. Ferromagnesian constituents are abundant, including dark-brown biotite in irregular foils, and black minerals with 

prismatic cleavage. The feldspar, which is of a light-gray color, 

constitutes about half the rock, while the quartz is not to be recognized macroscopically without careful search.

"Eruptive rocks cf Electric Peak and Sepulchre Mountain: Twelfth Ann. Rept. Q. S. Geol. 

Survey, pt. 1,1891, pp. 603-60T, PI. L.
SMITH ANDT TTFTPnaTf AVTTV . 71 CALKINS. J PEIROURA1 H.Y. II

Microscopically, accessory iron ore, apatite, and titanite are noted. 

The most abundant constituent is found to be plagioclase, which is 

chiefly labradorite, but it shows pronounced zonal structure, and a 

peculiar and characteristic mottled appearance in polarized light, 

owing to an irregular intergrowth of different forms of plagioclase 

with different optical orientations. The species thus intergrown vary 

from calcic labradorite to oligoclase.

The ferromagnesian constituents are greenish augite, rather palegreen hornblende, and biotite, which is strongly pleochroic and of a 

deep reddish brown color. The amphibole and pyroxene together 

slightly exceed the mica in quantity. The augite always occurs intergrown with hornblende, the former generally being in the. form of 

irregular areas inclosed in the latter,, with the vertical and ortho 

axes in common for the two minerals. The hornblende is massive, 

sharply marked off from the pyroxene, and is thought to be original. 

The biotite is also frequently intergrown with hornblende, the basal 

pinacoid of the biotite coinciding with the orthopinacoid of the 

amphibole.

Quartz, which occurs in the usual small anhedra, is scarcer than in 

the diorites already described, and orthoclase, in the usual interstitial relation, is a rare constituent.

The order of crystallization in the granodiorites and quartz-micadiorites is, in general: accessories, plagioclase, ferromagnesian minerals, quartz, and orthoclase.

Probably in close chemical relation to the quartz-diorite is a rock 

occurring on the ridge east of Granite Mountain. Macroscopically it 

differs from it considerably, being of a lighter grayish green color. 

The chief constituent .is gray feldspar with twin striations on the 

elongated basal cleavage faces. Subordinate to the feldspar is a 

dark gray-green mineral with prismatic cleavage.

Under the microscope the structure is seen to be medium grained, 

hypidiom orphic granular, and the essential constituents are found to 

be.plagioclase and amphibole, the latter perhaps in part secondary. 

There is a little interstitial orthoclase, but no quartz. A little biotite, 

iron ore, apatite, titanite, and epidote are also present. The titanite, 

in sharply developed crystals of rhomboidal section, is remarkably 

abundant. _The plagioclase, which is somewhat clouded by decomposition products, is similar in microstructure and in chemical composition to that of the quartz-bearing diorite just described.

GABBROS.

Olivine-hornblende-gabbro. This rock, found in the peripheral zone 

at Granite Mountain, is very dark in general hue, with ferromagnesian 

minerals in the aggregate predominant over feldspar. Under the 

microscope it is seen to be composed essentially of plagioclase, monoclinic pyroxene, olivine, and hornblende, this order being approxi-
72 CASCADE RANGE FEAR FORTY-NINTH PARALLEL.

mately that of relative abundance. The plagioclase and olivine are 

generally in the form of grains with irregularly curved boundaries. 

These are in wrapped, though rarely completely inclosed, by allotrioinorphic plates of pyroxene, with which the hornblende is intergrown.

The plagioclase, which is without zonary banding, shows in sections 

perpendicular to the brachypinacoid a maximum extinction angle of 

about 44°, indicating a composition near Abj An2 . It is but slightly 

altered.

The olivine is very largely decomposed to talc and serpentine, the 

process of alteration being attended by the usual separation of iron ore.

The pyroxene is in thin section almost colorless, with a faint tinge 

of green. An imperfectly developed cleavage is sometimes found 

parallel to the orthopinacoid.

The hornblende is partly green, partly deep brown. As already 

noted, it nearly always occurs in parallel intergrowth with the pyroxene, sometimes.included in that mineral in the form of small splinters 

or plates, but more frequently surrounding it. The boundary between 

the brown hornblende and the pyroxene is always absolutely distinct; 

that of the green amphibole is less evidently so, because of the similarity in color, but appearances indicate that all or nearly all of the 

hornblende is primary. The brown and green hornblende, however, 

frequently appear to grade into each other, and it is suggested that 

the latter may be derived from the former by some process of 

reduction.

There are irregular aggregates of actinolite which may arise from 

the decomposition of pyroxene or olivine.

Uralitic gabbro of Palmer Mountain. In the exposure east of the 

head of Palmer Lake this rock shows inacroscopically a marked ophitic 

structure of rather coarse grain. Microscopically the rock is found 

to consist essentially of plagioclase and hornblende. The amphibole 

is peculiarly mottled, its color in thin section varying from deep 

grass green to colorless. It is generally massive, but sometimes forms 

fine-grained aggregates. Although no pyroxene was found in the section, the ophitic relation of the hornblende toward the feldspar, in connection with the altered character of .the rock, is rather suggestive of 

derivation from pyroxene. The plagioclase is less basic than is usual 

in gabbro and apparently belongs to the andesine division. The feld: 

spar is rather badly decomposed, with the production of much calcite, 

mica, zoisite, and common epidote. No olivine seems to have been 

present in the rock, which apparently belongs near the acidic end of 

the gabbro family. " Uralitic gabbro of Mount Cliopaka. This rock is dark grayish 

green in mass and is texturally quite different from the gabbro of 

Palmer Mountain. The most prominent constituent is a green amphibole, which, instead of being ophitic, is in ragged prisms with a 

tendency to parallel arrangement. Under the microscope basic pla-
I PETROGRAPHY. ' *T3

gioclase is seen to be about equally abundant with the ferromagnesian mineral. -A little diallage is found, but it is always surrounded 

by the amphibole, and the latter appears to have originated in part 

or entirely from the decomposition of pyroxene. It is deep to pale 

green, often fibrous, and with fringe-like borders. The feldspar has 

also undergone alteration, chiefly of a sort that indicates the agency 

of deep-seated forces rather than ordinary weathering. The large 

individuals are often changed to fine mosaics of clear grains, though 

the original twin striations, with crenulated borders, in some cases 

remain visible. Throughout the generally clear feldspar minute needles of green amphibole, evidently secondary, are thickly interspersed, 

and grains of zoisite are disseminated in moderate abundance. There 

are no vestiges of olivine in the rock.

ULTRABASIC KOCKS.

Serpentines and pyroxenites of Mount Cliopcika. These rocks are 

deeply altered, often containing no remnants of the primary minerals, 

one specimen being found to consist essentially of dolomite, serpentine, and talc, showing no traces of the original texture.

In another interesting rock the chief constituent is an amphibole 

almost colorless in thin section, and probably to be referred to treinolite. This rock also contains some diallage, enstatite, and serpentine 

with felted structure which may represent olivine. The treinolite 

occurs partly in moderate-sized, extremely irregular individuals, but 

much of it is finely granular. Occasionally it surrounds diallage 

with parallel orientation, and may be derived from the alteration of 

the pyroxene by a process similar to uralitization.

Saxonite of Ruby Creek. The ultrabasic rocks of Ruby Creek are 

dark gray-green granular aggregates in which silvery-bladed crystals 

of enstatite are more or less prominent megascopically. Under the 

microscope the essential constituents are found to be olivine and 

enstatite, sometimes one and sometimes the other predominating. 

Grains of deep-broAvn chromite or picotite are also present. Decomposition has affected the rock only to a moderate extent. The most 

important secondary constituent is talc, Avhich is epigenetic upon both 

olivine and enstatite, but serpentine accompanied by secondary 

magnetite is replacing olivine in the usual manner.

HYPABYSSAL ROCKS. 

CLASSIFICATION AND DISTRIBUTION.

We have now to consider a large number of dike rocks, of great 

petrographic diversity, which have no known connection with volcanic flows, and are usually in evidently genetic relationship to plutonic masses. Passing by the apophyses from intrusive masses, differing from the parent rock only in texture, Ave shall discuss here only a
CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BULL. 235.

group of rocks supposedly produced by secondary differentiation from 

large bodies of magma. In period of intrusion these are not widely 

separated from the bathblithic masses, and are generally distinctly 

more acidic or more basic than the parent rock. Thus they fall chemically into two groups, the one comprising the acidic granite-porphyries, 

aplites, and pegmatites, and the other a variety of basic dike rocks 

which may be designated in the broad sense of the term lamprophyric. 

The occurrence of the rocks of these groups represented in our collection is indicated in the following table:

Species, dixtribution, and occurrence of the hypabyssal rocks of the region.

Species

Do.. ...........

Soda-rich graniteporphyry.

Do.............

Do..... ....--..

Granite-aplite ......

Granodiorite-aplite . 

"Soda-syenite" ....

Do.............

Do.............

Do...."........

Hornblende-porphyries.

Diorite (?)..........

' ' Mica-diabase " . . . .

Peridotite ..........

Locality.

Near Barren ..........

East of Pasay ten River . 

Granite Mountain . ....

Between Wenatchee

and Entiat. 

Okanogan Mountains . .

.....do ................

West of Loomis, and 

near Mamie Pass. -

South of Bighorn Peak. 

Near Orondo ..........

East end of Horseshoe . .

Mount Remmel ........

West of Hidden Lakes.

Main divide, head of 

Canyon Creek.

Granite Mountain .....

Near Orondo ...........

North of Park Pass ....

Mode of occurrence.

granodiorite. 

Dikes in granodiorite.

Dikes in Pasayten formation.

Do. 

Dike in diorite; periphery of acidic

granodiorite. 

Dikes in schists and gneisses.

Dikes in biotite-granite.

Do.

Dikes associated with granodiorite. 

Dike in granite or granodiorite.

Dikes in diorite.

Dike in granite.

Dike in Pasayten formation.

Dikes in Pasayten formation.

odiorite. 

Dike in schist.

ACIDIC DIKE ROCKS.

Granopliyre. This rock, collected at Orondo, shows, megascopically, a very few small crystals of feldspar and quartz in a dull-white 

aphanitic groundmass, which is slightly speckled with limonite. 

With the aid of the microscope it is found that this groundmass is 

granophyric and composed of quartz and alkali feldspars. There are 

no ferromagnesian minerals.
PETROGRAPHY. 75

Grranite-porpliyries. In Antoine Coulee the granodiorite is cut by 

dikes of a handsome porphyry, which exhibits raacvoscopically abundant phenocrysts of feldspar and quartz, with small dark-green 

specks, in a gray aphanitic groundmass. In the thin section it is 

found that the most numerous phenocrysts are of oligoclase, while 

there are many small ones of altered biotite. There is a small proportion, however, of large phenocrysts of orthoclase, intergrown with 

quartz and poikilitically inclosing crystals of plagioclase-and biotite. 

The groundmass is composed, of quartz and alkali feldspar of rather 

peculiar structure, abundant irregular areas of micropegmatite being 

embedded in a microgranular paste.

Of the numerous. dikes in the vicinity of Barren a very common 

type is composed oil.a porphyritic rock, with abundant phenocrysts of 

quartz and feldspar in an aphanitic groundmass, dull white except 

for frequent stains of limonite. It is found by study of the thin section that the phenocrysts are quartz, orthoclase, and less plagioclase,

in a holocrystalline groundmass composed of qviarte and alkali feldspar in pseudospheru I itic in tergrowths.

Other dike rocks of similar megascopic appearance are found in the 

eastern portion of the same belt of Cretaceous rocks, which are, however, apparently richer in soda. The feldspar phenocrysts are all 

striated and belong to the species oligoclase-albite. The groundmass. 

consists in the main of quartz in broad irregular individuals inclosing laths of feldspar, but there is also a little microgranular interstitial material.

The quartz-porphyry occurring on Granite Mountain, in the Mount 

 Baker district, appears likewise rich in soda. It shows, in a white 

aphanitic groundmass, phenocrysts of striated feldspar, small grains 

of green ainphibole, and quartzes whose outlines are rounded by corrosion in a striking manner. The phenocrystic feldspar is determined 

microscopically to be oligoclase, but it' is veined with a colorless 

mineral having very nearly the same refractive index and double 

refraction and without twinning, which may be orthoclase. The 

groundmass consists of quartz and feldspar in micrographic intergrowth. Noteworthy is the occurrence of a comparatively large 

amount of titaiiite in irregular grains.

Pegmatites. The pegmatite intrusive in the schist below Entiat is 

composed of dominant orthoclase and quartz, with a little acidic plagioclase, considerable inuscovite, and numerous crystals of garnet 

ranging in diameter from one-half millimeter to 5 millimeters. .The 

rock has undergone dynamic stresses, which have produced schistose 

and niylonitic structures, but no such marked effect as the complete 

foliation produced in the schist itself.

A specimen of graphic granite collected near Mount Remmel and 

south of Park- Pass is composed of a large individual, of pink potash 

feldspar, which is found microscopically to consist of inicrocline with 

veins of striated feldspar, presumably albite. Included in this mineral
76 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BULL. 235.

are crystals of acidic plagioclase, quartz, and muscovite. Contrary 

to the usual rule, however, the quartz individuals have not a common 

orientation, although they appear macroscopically in cuneiform 

figures.

At several localities a sort of ribbon structure was observed in the 

small pegmatitic veins. The borders were fine grained and aplitic in 

texture, the next zone inward pegmatitic, and the center formed by a 

rib of pure quartz. 

Aplites. The aplites associated with the mica-granite have the 

usual mineralogic composition. Quartz is abundant, and the potash 

feldspars (orthoclase and microcline, often perthitic) ^predominate 

over the acidic plagioclase.

An aplitic rock of different type cuts the greenstones northwest of 

Loomis. The essential constituents are feldspar, much quartz, and a 

little biotite. The potash feldspar is inferior in amount to the-plagiov clase, which ranges from andesine to acidic oligoclase. Thus4he rock 

shows a chemical relationship to the neighboring granodiorite, from 

which it is probabty derived. It appears that the aplites resemble 

their parent magmas in regard to the proportion between the alkalies. 

. '' Soda-syenite. " The rock from Bighorn Peak referred to as '' sodasyenite " is a rare type and apparently is the product of an exceptional 

kind of differentiation from a granitic or granodioritic magma. It is 

very light colored and of moderately fine granular texture. Under 

the microscope plagioclase is seen to form much more than half the 

rock; the other essential constituents are orthoclase and quartz in 

about equal quantity. .There are also some green rhombic pyroxene 

and deep-green hornblende and iron ore, nearly equal to one another 

in amount, but their aggregate quantity is very small, and they may 

be considered accessory. Apatite and zircon are present as minor 

accessories.

The plagioclase, in polarized light, is remarkable for the fineness

and regularity of its .polysynthetic twinning after the albite law. A 

section almost strictly normal to the bisectrix showed a rather faintly 

defined zonal structure. The core gave an extinction angle of + 4°, 

while the broad external zone, constituting the greater portion of the 

crystal, extinguished at +9°. These angles correspond, respectively, 

to the compositions AbgAiij and Ab^i^. The orthoclase is in the 

usual interstitial relation and the plagioclase is usually idiomorphic 

against it, but not infrequently the boundary'bet ween the two feldspars is irregularly curved, and they sometimes appear to be intergrown. The p*yroxene and amphibole are generally in parallel 

intergrowth, and the iron ore is mostly associated with them.

LAMPROPHYRIC DIKE ROCKS.

General characteristics. The lamprophyric rocks of the collection 

comprise a wide variety of types, most of which find no place in the 

classification of lamprophyric rocks proposed by Rosenbusch. The
PETROORAl'HY. ° 77

only general statements that' may be made in regard to them are thai 

they invariably show a decided predominance of! plagioclase over 

orthoclase and are rarely very rich in biotite; thus they do not seem 

to have the large percentages of potash that characterize most of the 

rocks that have been described as lamprophyres.

Diorite-porpliyries. Rocks of this type containing quart/ are 

apparently the most abundant lainprophyric rocks found. A dark, 

fine-grained, porphyritic rock cutting the white gneiss of Mount Reininel contains a very few phenocrysts of labradorite in a holocrystalline gronndinass which consists chiefly of strongly zoned plagioclase 

(andesine to acidic oligoclase) in idiomorphic prisms, and which con 

tains considerable biotite and a smaller amount of deep-green hornblende occurring in small ragged individuals. The final products of 

crystallization are a small amount of quartz and an alkali feldspar, 

commonly in micrographic intergrowth.

The diorite collected at Orondo is of a similar type. The dike in 

the Cretaceous rocks west of the Pasayten is apparently somewhat 

move basic, carrying phenocrysts of zoned plagioclase (labradorite to 

andesine) and brown hornblende in a holocrystalline groundmass of 

plagioclase laths, a little quartz, and perhaps a second generation of 

hornblende. The diorite-porphyry from the Horseshoe has phenocrysts 

of zoned plagioclase (labradorite with more acidic shells), greenishbrown hornblende, augite (usually with borders of hornblende in parallel position), and biotite. The groundmass consists of the same 

minerals, together with some interstitial quartz and alkali feldspar.

Hornblende-porphyries. Interesting specimens of this character 

were collected from dikes cropping out along the divide north of Barron. One of these is characterized by the- presence of large phenocrysts of dark-green hornblende, Avith strikingly perfect crystal form. 

The microscope shows the presence of feldspar, apparently in two 

generations, although forming no prominent phenocrysts. There is a 

little green monoclinic pyroxene intergrown with the hornbleude, as 

well as considerable iron ore and apatite. A little quartz is present 

in the holocrystalline groundmass.

Another rock from the same vicinity also shows, megascopically, 

abundant pheuocrysts of amphibole in a crystalline groundmass. 

Under the microscope it appears that the groundmass is holocrystalline, consisting of feldspar, a little quartz, and small well-developed 

prisms of pale-green diopside. The amphibole is of especial interest, 

for the phenocrysts are found to be parallel intergrowths of two 

varieties. The more, abundant is a colored hornblende, mainly deep 

brown, but shading into green near its borders. The other amphibole 

is colorless in thin section. It forms irregular areas within and borders about the colored variety, from which it is sharply marked oft!. 

Both minerals have an extinction angle of about 21°, but the colorless 

variety has a notably higher double refraction than the other. A 

small amount of diopside is also intergrown with the amphiboles.
78 * CASCADE EANGE NEAE FOETY-NINTH PAEALLEL. [BULL.235.

The rock is considerably altered, containing much chlorite, and the 

feldspar is mostly too much decomposed for determination, but in 

some specimens shows albite twinning and high extinction angles.

Diorite (?) of Granite Mountain. A dike rock associated with the 

granite at Mamie Pass is peculiarly interesting by reason of its mineralogic constitution and the structural relations of some of the 

accessories.

Megascopically it appears fine grained, though evidently crystalline. The color of the bulk of the rock is almost black, but there are 

oval and circular spots that are nearly white and stand out upon the 

weathered surfaces.

Under the microscope the essential constituents are seen to be, in 

order of abundance, feldspar; quartz, biotite. Green hornblende, 

iron ore, apatite, and titanite occur as accessories, though all in comparatively large amount. All the minerals are fairly fresh. Some 

epidote occurs in a rather peculiar manner, which will presently be 

described. The texture in the main is fine grained, hypidiomorphic 

granular, though a few feldspars stand out porphyritically. The 

whitish spots seen macroscopically are areas where quartz is' unusually abundant and mica almost absent. :

The plagioclase, which is idiomorphic and prismatic in the direction of the a axis, has a strongly marked zonal structure. The kernels of the crystals are andesine and the rims very acidic; the outermost portions, indeed, are often without the albite twinning found in 

the centers and may be of alkali feldspar. The mica is of a peculiar 

olive-gyeen color, but, like ordinary biotite, has straight extinction, 

high double refraction, and a very small optic axial angle. It occurs 

in peculiar radiating brush-like aggregates. The quartz is abundant 

and forms moderately large allotriomorphic individuals:

The most noteworthy feature of the rock consists in the anomalous

position of the apatite and the titanite in the sequence of crystallization. The titanite, which occurs in comparatively large individuals, 

frequently is penetrated by the idiomorphic crystals of feldspar. In 

one case titanite was observed inclosing quartz with polygonal outline, but generally it is idiomorphic against quartz. . The apatite, 

however, never shows a suggestion of crystal form. It occurs in 

broad, irregular plates, allotriomorphic against feldspar and biotite. 

In fact, the apatite, Avhose identification was based on the combination of high refractive index with weak double refraction, and confirmed satisfactorily by microchemical tests, plays a role very 

analogous to that of the quartz and is evidently one of the last products of crystallization.

The epidote occurs in veinlets and small inclosed areas, bordered 

by a fine .aggregate of feldspar, quartz, and magnetite. It is supposed to be of the nature of vein material, filling spaces produced by 

dynamic brecciation of the rock.
- PETROGRAPHY.. 79

Diabases. A specimen collected by Professor Russell near Ban-on. 

seems to be a normal diabase. It consists mainly of plagioclase and 

violet-brown titaniferous augite in the usual ophitic relation. There 

is much iron ore,-and there are in asses of iddingsite that appear to 

be pseudomorphs after olivine.

A rock collected near 0rondo is of a different and quite unusual 

type. The leading constituents are labradorite and augite, but there 

is also considerable biotite and a little quartz. The lath-shaped plagioclase and rather irregular foils of biotite are inclosed ophitically 

by the augite, while the quartz is interstitial. The rock is decidedly, 

different from the Yakima basalt which caps the plateau above this 

locality, and probably lias no genetic relation with that lava.

Peridotite. A rock apparentty intrusive in the granite north of 

Park Pass attracted especial notice in the field by reason of its strong 

effect on the magnetic needle of the plane table. It is a dark-colored

granular rock of high specific gravity, which proves under the

microscope to be an exceptionally fresh peridotite.

Olivine is the most abundant constituent, while diallage is next in 

order of abundance. Bordering the areas of diallage and included 

within that mioieral are small particles of a nearly colorless amphibole, 

the associated minerals always having their vertical and ortho axes in 

common. The amphibole is always massive and the boundaries 

between it and the diallage are always sharp; their relation seems, 

therefore, to be that of intergrowth rather than paramorphism. A 

little rhombic pyroxene (bronzite) is also present. The olivine is partially altered to a yellowish brown serpentine associated with a large 

proportion of secondary magnetite. The texture is that characteristic 

of the peridotites, the pyroxenes and amphibole occurring in irregular 

plates interstitial between the large rounded grains of oliviue.

CONCLUSIONS. 

PRELIMINARY STATEMENT.

The Cascade Mountains near the forty-ninth parallel are composed 

in greater part of igneous rocks that belong mainly to great batholitliic masses of rather acidic composition. In areal extent the batholiths of this region are perhaps exceeded by few examples, arid are. 

quite comparable with the immense intrusions of. the Sierra Nevada. 

To the student of batholithic magmas the Northern Cascades afford a 

most interesting field, and future workers there may obtain data bearing on such important theoretical questions as the normal succession 

of eruptive rocks, the laws and phenomena of differentiation, the 

'mechanics of igneous intrusion, and the geographic relations of petrographic provinces.

Few data bearing 011 such. broad problems were gathered by the 

present writers, but it seems justifiable (1) to consider briefly here
80 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [uuLL.235.

s * 

some phenomena supposed to illustrate differentiation on the margins

of batholithic masses and (2) to point out the apparent significance 

of certain relationships and general characteristics exhibited by the 

igneous rocks described on the preceding pages. As.the reader hardly 

need be reminded, theoretical speculation based on reconnaissance 

observations and 011 microscopic study unsupported by chemical data 

can not properly be carried far. The object of the considerations 

which follow is to point oat in connection with each of the points considered what appears to the writer the most probable bearing of the 

available evidence.

EVIDENCES OF MARGINAL DIFFERENTIATION.

The existence of basic peripheral zones in several intrusive masses 

has already been noted briefly, but consideration of their origin has 

been reserved for this place. The most notable examples were 

observed at two localities in the valley of the Columbia and about 

Granite Mountain in the Mount Baker district.

Columbia River Valley. The phenomena at both localities in 

Columbia River Valley were only observed in passing, but there 

appeared to be in both cases granodiorites irruptive into schists and 

gneisses, which are not notably more basic than the intrusive rock. 

The peripheral part of the intrusive mass is very variable, but on the 

whole decidedly richer in ferromagnesian minerals than is the typical 

granodiorite away from the contact. The basic material is cut by 

innumerable dikes of more acidic material. There is no evidence at 

these localities of marginal absorption, and differentiation is suggested 

as the most probable explanation of the facts. The observed phenomena seem to indicate that a marginal basic zone was formed, 

partly solidified, and then broken up and injected with more acidic 

material from the still liquid interior portion of the mass.

Granite Mountain. At this locality the phenomena are better 

exposed and have been studied more closely than in the case of Columbia River localities, though still very incompletely. The field observations and the results of petrographic study of the specimens collected may be summarized as follows:

(1) The intrusive rock at a distance from the contact is an acidic 

granodiorite of fairly uniform character (which may be referred to as 

the normal type).

(2) The peripheral portion of the intrusion is very variable and 

more basic on the whole than the normal granodiorite.

(3) The rocks of the peripheral zone comprise granodiorites, diorites, 

and gabbros, showing close petrographic relationship to the normal 

granodiorite and to one another.

(4) The rocks into which the igneous materials were intruded are 

metaniorphics, chiefly of sedimentary origin, not notably more basic 

than the normal granodiorite.
SO£KINS.D ] PETROGRAPHY. -81

(5) There is no evidence of any considerable assimilation of the 

metamorphics by the igneous rock.

There is a lack of chemical data in regard to the constitution of all 

the rocks concerned, which is counterbalanced to a greater extent for 

the igneous than for the metamorphic rocks by microscopic study. 

It seems altogether improbable, however, that the peripheral rocks 

could have been formed by assimilation, especially in view of the fact 

that no physical evidences of assimilation were observed. The close 

consanguinity of the rocks of the peripheral zone can not be .devoid 

of significance, and seems to point to differentiation as the most probable agency concerned in the production of the various species.

In regard to the details of the process, our field notes afford little 

evidence. There is certainly not any such regular concentric arrangement of zones as occurs, for example, at Togo Peak/1 nor was evidence 

obtained of distinct intrusion of one rock by another.

RELATIONSHIPS AND GENERAL CHEMICAL CHARACTERS OF THE IGNEOUS ROCKS.

The petrographic descriptions have, it is hoped, brought out the 

fact that the igneous rocks of the region show certain family traits in 

common. This point is most clearly illustrated by the plutonic rocks, 

which are most fully represented by specimens, and the chemical 

. characters of which are most capable of inference from the mineralogic composition. We have, therefore, in order to exhibit their relations most graphically, constructed the following table, in which the 

well-defined types of plutonic rocks represented by fresh specimens 

are arranged in order of acidity and their essential mineralogic constitution shown.

nPirsson, L. V., Geology of Little Belt Mountains: Twentieth Ann. Kept. U. S. Geol. Survey 

pt. 8, p. 564.

Bull. 235 04 6
Quantitative illations of essential minerals in plu

Rock.

rite.

Olivine-horiiblende-gabbro

Quartz.

Much ........

.....do........

.....do........

Little ........

Little ........

Orthoclase.

....do...

....do...

....do...

little.

Plagioclase.

clase.

.....do. .......................

.....do......:.;...............

.....do..................:.....

Muscovite.

accessory.

Biot

..... do

.....do
PETROGRAPHY. 83

With the table before us it is easy to point out the following important facts:

(1) The rocks form a graded series, each closely related to its neighbor and varying from one end of the series to the other according to 

definite/laws. With few exceptions, each essential constituent either 

decreases or increases in importance as we pass from the most acidic 

toward the most basic type.

(2) There is an absence throughout the series of alkaline rocks 

allied to syenite, essexite, shonkiriite, etc. The rocks in this table 

all belong to the granite-dioritic and gabbro-peridotitic magmas of 

Rosenbusch.

(3) It is noteworthy that even among the granites there are no rocks 

in which potash feldspar predominates markedly over plagioclase.

We may now consider briefly how far the other classes of igneous 

rocks shONv similar relationships and general characteristics.

The volcanic rocks fall into a graded series, passing from rhyolite 

through dacite and andesite to basalt, without including any trachytes 

or other alkaline types. Corresponding to the absence of granitic 

rocks with dominant potash feldspar is the absence of rhyolites in 

which phenocrysts of orthoclase play an important part.

The hypabyssal rocks show less complete gradation and less evident relationships than the plutonics and volcanics. Some of themost acidic have abundant orthoclase phenocrysts, while in others 

apparently as acidic the phenpcrystic feldspar is plagioclase. The 

"soda-syenite" of Bighorn Peak also shows exceptionally an alkaline composition, and many of the pegmatites have orthoclase as the 

dominant feldspar. In short, many of the hypabyssal rocks, chemic- 

.ally considered, would fall outside of the series formed by the plutouic 

and volcanic rocks. This apparent discrepancy is explainable, however, by supposing that the hypabyssal rocks are the product of differentiation of a higher order than that which produced the others, 

and does not affect the significance of the close relationship betAveeri 

the various volcanic and plutonic rocks.

The facts that have been set forth in the preceding paragraphs 

appear to have the following important consequences: The igneous 

rocks of the region show in general a close consanguinity, and their 

variations follow definite laws. This fact appears to indicate that 

they were all derived from a homogeneous magma. If this be true, 

this parent magma, as indicated by the composition of the derived 

rocks, was characterized chemically by relatively low. content of alkalies and predominance of soda over potash.

It is worthy of note that the assertions of the last paragraph seem 

applicable also to the .rocks of the Sierra Nevada, of eastern Oregonj 

and of the more southern portions of the Cascades. In other words, 

the regions in question all belong to a single great petrographic 

province. .
84 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [nuLL.235.

STRUCTURE.

GENERAL FEATURES.

In a general way the Cascade Mountains at the forty-ninth parallel 

may be said to consist of a synclinorium. As far as age relations 

are known the oldest rocks occur upon the extreme east and extreme 

west flanks of the range, being the slates and greenstone of Okanogan 

Valley and the schists on the boundary north of Maple Falls. Both 

the east and the west sides of this synclinorium are anticlinal, for 

Tertiary rocks occur resting against these oldest rocks. The large 

area of Cretaceous strata, the Pasayten. formation, constitutes the 

.central portion of the synclinorium, and minor synclines and anticlines will undoubtedly be worked out eventually; indeed, their position can be suggested from the results of this reconnaissance.

The presence of intrusive rocks in large masses naturally makes 

the structural relations less apparent than would be the case in a 

mountain range including only stratified rocks. The batholith of 

granitic rocks which makes up the Okanogan Mountains is perhaps the 

most important igneous member of the Cascades. Little can be definitely determined as to the original upper limit of such a batholith; 

but if the intrusive contact was approximately horizontal, the present 

relations indicate the subsequent development of an anticline that 

forms the eastern limb of the synclinorium mentioned above. These 

relations are: The intrusive contact, or upper surface of the granitic 

batholith, has an elevation of from 1,000 to 2,000 feet at Lake Haipwil, 

where the granodiorite is quite involved with the older rocks; a few 

miles farther west, on Mount Chopaka, it is at least 5,000 feet higher, 

while west 'of that the intruded rocks disappear, altogether.

If, on the other hand, the upper limit of the granitic magma did 

not approach in any degree a horizontal plane, then the remnants of 

older rocks resting upon the intrusive rocks may represent portions 

of an older anticline or possibly owe their present position to elevation resulting from the invasion of this magma. In either case it 

appears justifiable to consider the granite mass as playing the role of 

an anticline between the Okanogan Valley depression containing 

Tertiary sediments and the Pasayten Valley area of Cretaceous strata.

FOLDS IN THE PASAYTEN FORMATION.

The portion of the Hozoraeen Range which is made up of this formation may be described as anticlinal. Along Pasayten Valley the 

dips observed were all°to the east and northeast. On Chuchuwanten 

Creek a minor syncline is a probable element in the structure, 

becoming more important novth of the boundary. The main anticline 

is well shown at the head of Canyon Creek, where the axis is in the 

valley. North of this the rugged crest, which forms the main divide, 

is composed of conglomerate with a steep western dip (PI. II, B),
SMITH AND~| QTVRTTnTirRTT 8 ^ CALKINS. J STKUCIUKE. 50

.while to the south the divide is on the eastern dip. This fold has a 

general north-south trend, and the western limb of the anticline 

extends well down Slate Creek, so that the so-called slate on that 

creek and on Canyon Creek have the same west dip as the similar 

shales at the head of Three Fools Creek and are believed to represent the same portion of the Pasayten formation. West of the intrusive diorite on Ruby Creek the dips in the altered shale are steep, 

indicating possible reduplication of the strata by close folding. This 

compression would account largely for the degree of alteration noted 

here, by which the rocks appear older than the shales near the 

divide.

In the quartzite, slate, chert, limestone, and schists of Skagit Valley the structural relations Avere not worked out. On Devil Creek 

the Cretaceous shales appeared to overlie unconformably these older 

rocks; Near the mouth of Lightning Creek the chert, quartzite, -and

schist, while much broken, appear to show a general east-west structure, while in the schists farther south the schistosity trends more 

north-south.

STRUCTURE IN THE MOUNT BAKER DISTRICT.

The older rocks in the eastern part of this area are closely folded 

and the structural relations could not be ascertained in the rapid 

reconnaissance. The general trend of the structure is probably not 

far from north-south. Northwest of Mount Shuksan the shale and 

sandstone beds are vertical and strike N. 40° W. Farther north, on 

the peaks south of Twin Lakes, the schists and associated rocks strike 

N. 5°-30° E. and show steep dips both to the east and to the west. 

The structure here is doubtless a closely compressed anticline, with 

its axis near Twin Lakes. This type of folding may be regarded as 

characteristic for this region.

In his more careful survey of the area immediately north of this 

Daly" has been able to determine the structural relation's in similar 

rocks which are of Paleozoic age. The axial direction of the folds 

there is east-west, and northwest-southeast faults are responsible for 

a fivefold duplication of beds.

Along the North Nooksak the sedimentary rocks appear younger 

and the structure is much less involved. The Eocene strata farther 

west are only moderately folded and appear to occupy embayments in 

the older schists.

PHYSIOGRAPHY.

SCOPE OF DISCUSSION.

The earlier geologic history of this northern portion of the Cascade 

province has been broadly outlined in the foregoing descriptions of 

the formations and their structural relations. The present attitude

« Summary Report Geol. Survey Canada, 1901, p. 46.
86 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BULL. 235.

of the Cascade Range and the origin of its topographic features, however, are to be attributed to geologic action of more recent date than 

any of the rocks described except the Mount Baker lavas. Certain 

observations were made on the physiography of the region which may 

bear upon the broader problem of the origin of the ranges of the 

Pacific slope. In this discussion reference will be made to the nature 

of the uplift by which the Cascade Range received its present elevation, and also to the vigorous erosion by which these mountains have 

been sculptured to their present form. In the latter process glacial 

action has been most important.

In the boundary section of the Cascade Range the only rocks known 

to be younger than the Cretaceous are the andesitic lavas which appear 

to overlap the Pasayten formation on the east, and therefore to be 

somewhat younger. The very late lavas from Mount Baker are 

excepted in this statement. Farther south, however, Miocene lavas 

and sediments are involved in the very heart of the range, which is 

known to have been uplifted somewhat after the close of the Miocene.

The Cascades therefore constitute a relatively young range, and it 

becomes of importance to determine if any traces remain of the 

uplifted surface.

RECOGNITION OF A PENEPLAIN SURFACE.

The difficulties attending the search for topographic features antedating the uplift of the Cascades have been succinctly stated as follows by Daly in his preliminary report : a

All indications point to the fact that erosion is responsible for the existing form 

of these mountains. No constructional surfaces other than those slopes assumed 

by moving rock waste have been recogrized in the belt; no fault sc'arp or fold 

recent enough to have preserved any of its original form, even in a damaged condition. , has been observed. Vigorous dissection by denuding agencies has removed 

a vast volume of rock from the structurally complex range. Yet the existing

diversity of relief can not be far from the maximum due to the cycle of degradation through which the mountains are now passing.

The area thus described is not exceptional in the degree of dissection attained, yet it is adjacent to a region where the best evidence of 

an older surface can be seen. Standing on the summit of the peak 

immediately south of Twin Lakes, in the Mount Baker district, at an 

.elevation of approximately 6,000 feet, one can'see two types of topography. To the north and east the peaks are acute and the ridges serrate, so that the sky line presents a most irregular aspect; to the west 

the sky line is even and the region as far as the eye can see appears 

a high plateau upon which rests the white cone of Mount Baker. 

More careful observation shows that this apparent plateau is composed of flat-topped ridges, with a somewhat uniform elevation of 

5,000 to 6,000 feet and a gentle westward inclination, between which

"Summary Report Geol. Survey Canada, 1901, p. 41.
SMITH AND" 

CALKINS. PHYSIOGRAPHY.

are the deep, steep-sided canyons of the North Nooksak and its tributary streams..

These ridges have rather broad crests, of smooth and grassy character, in marked contrast to the valley walls below and to the cliffs, 

pinnacles, and crags a few miles farther east. The completeness of 

dissection or maturity of relief- that characterizes the latter case is 

most plainly not yet attained in this adjacent area, since here there 

exist remnants of the topography that apparently antedated the present cycle of erosion.

The recognition of this older surface agrees with the results of the 

physiography study of other parts of the Northern Cascades/' Before 

the uplift which inaugurated the erosional activity which lias so

FIG. 1. Plateau representing uplifted lowland surface; western portion of Skagit Mountains, 

with Mount Baker; looking west from Bear Mountain.

thoroughly sculptured most portions of the range, the Cascade area 

had been more or less thoroughly reduced to a lowland. Where this 

old lowland surface has been recognized the degree of peneplanation 

appears to have been fairly perfect, with relatively few monadnocks 

remaining above the general surface. Uplift of this lowland-gave 

opportunity for the streams to intrench themselves and to cut deep 

canyons, as in the vicinity of Mount Baker. Where the uplift reached 

its maximum, as in the more eastern portion of the Skagit Mountains, 

the rock mass was brought into the zone of most effective erosion 

and the work of dissection was more rapid, reaching within the same 

period a more mature stage in the topographic cycle than where the 

u plight was less in amount. Expressed more definitely, where the 

change in elevation was only 5,000 to 6,000 feet remnants of the 

uplifted surface remain and can be seen in the broad, flat divides;

a Smith, G. O., and Willis, Bailey,.Geology of Washington: Prof. Paper U. S. Geol. Survey No. 

19,1904.
88 CASCADE EANGE NEAE FOETY-NINTH PAEALLEL. [BULL.2&.

where it was 7,000 feet and over no traces of the old lowland persist, 

the peaks being acute pinnacles and the divides mere knife edges. 

This difference can be seen by comparing" the views illustrated in 

fig. 1 and PL IV, B, the point of view being the same.

In other parts of the boundary section identification of the old 

lowland surface has been less certain. In the Okanogan Mountains 

there is an approximate uniformity in the heights of the prominent 

peaks,-which are about 8,000 feet, and in several cases' the summits 

exhibit flat surfaces that suggest an older topography. A case of this 

kind is Ampitheater Peak, illustrated in PI. Ill, A, where the steep 

slopes are in marked contrast with the fairly level top. This feature 

is especially noticeable from the summit of Cathedral Peak (PI. Ill, B), 

which itself has an even-topped shoulder at the same elevation as 

the top of Ampitheater Peak.

In the Hozomeen Range, near the head of Three Fools Creek, there 

are several long spurs with approximately the same elevation, that 

extend westward from the crest. PI. II, B, shows the beginning of 

two of these spurs, from a point on the third. The crest here is 

extremely rugged, and the coarse conglomerate which composes it is 

a rock that would naturally form monadnocks above the lowland 

surface, which may be represented by the crests of these long spurs. 

The Cretaceous rocks here are steeply inclined, and the structure 

could not determine the form of the spurs.

PHYSIOGRAPHIC SUBDIVISION OF CASCADE RANGE.

The subdivision of the northern portion of the Cascade Mountains, 

as proposed on page 14, appears to possess some basis in the physiography of the range. It has been thought probable from the observations in other parts of this mountain range that the uplift was 

effected not by a simple broad elevation of the lowland surface, but 

by an upwarp which in some areas at least was complex in character

and comprised upwarps along several parallel axes. So, in this .northernmost part of the Cascades, the Okanogan Mountains, Hozomeen 

Range, and Skagit Mountains may represent distinct upwarps separated by downwarps which determined the position of Pasayten and 

Skagit rivers. Along these relatively lower lines the valleys of 

these rivers have been eroded, so that the broad valleys are not to be 

considered as indicating the altitude of the downwarped surface, but 

only the positions of such axes.

The valley of the west fork of Pasayten River is a broad feature, 

quite different in type from the valley of the West Ashnola or of the 

other fork of Pasayten River. This may be in part due to the difference between the Cretaceous sediments and the granite and andesite of the other valleys, but the hypothesis that it represents in part 

a down warp'seems plausible. The divide between this valley and 

Chuchuwanten Creek is broad and flat-topped and possibly approxi-
U. S. GEOLOGICAL SURVEY IULLETIN NO. 235 PL. Ill

A. AMPHITHEATER PEAK, OKANOGAN MOUNTAINS. WASHINGTON. 

-'; - ".-," Sculptured by glacial cirques.

B. CATHEDRAL PEAK, OKANOGAN MOUNTAINS, WASHINGTON.
PHYSIOGRAPHY. . 89

mates the actual warped surface, inclining upward to connect with 

some rather even-crested spurs on the flanks of the Hozomeen Range. 

Another argument for the downwarp hypothesis for the Pasayten Valley is that this axis probably finds its continuation southeastward, 

in Methow Valley, where Mr. Willis has believed a similar downwarp to exist. The existence of a depression between the Hozomeen 

Range and the Skagit Mountains is even more hypothetical. It must 

be noted, however, that the valley of the upper course of Skagit River 

is a broad feature as compared to the deep canyon below, where the 

river turns west and crosses what is considered the axis of the upwarp 

of the Skagit Mountains. This canyon is one of the wildest gorges in 

the whole Cascade region and is similar in scenic beauty to the betterknown Frazer River Canyon.

There is a suggestive parallelism between this warping of the postMiocene lowland surface and the older structure of the range. The

upwarp slope that so abruptly differentiates Mount Chopaka from

Okanogan Valley appears to correspond, with the structure, as described 

on page 84. Thus the upwarp of the Okanogan Mountains follows 

apparently an anticlinal axis, and the downwarp that is supposed to 

adjoin it on the west accords in position with the broad syncline by 

.which the younger rocks of Cretaceous age are infolded in the range. 

The highest parts of the Hozomeen Range, which lie west of the 

divide, are also composed of older rocks, and this anticlinorium extends 

probably to the western slope of the Skagit Mountain upwarp. This 

parallelism between the old structure and the later warping can only 

be mentioned in this provisional way, since what is at present known 

of the structural and physiographic relations is insufficient to warrant more definite or conclusive statements.

RELATION OF CASCADE MOUNTAINS AND INTERIOR PLATEAU.

One other characteristic of'this portion of the Cascade Mountains 

must be mentioned. The remarkable manner in which these practically stop at the boundary has already been described. This proini-. 

nent feature in the orography of the western border of the continent 

was recognized by G. M. Dawson, who especially states that the Coast 

system of British Columbia should not be- confounded with the Cascade Mountains of Washington, as the former " replaces and partially 

overlaps" the latter."

Thus it is the interior plateau of British" Columbia which is found 

immediately north of the Cascade Range, the forty-ninth parallel being 

the approximate line of division between these two diverse topographic 

provinces. The reason for this abrupt change can be found, possibly? by the extension of the hypothesis worked out in the physiographic study of the Cascade Range in central Washington. There 

the upwarped surface of the Cascades gradually slopes down until it

a Trans. Royal Soc. Canada, sec. 4,1890, p. 4.
90 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [HUH,.235.

reaches the plain of the Columbia and the marginal warpings of the 

old peneplain surface merge into the even plateau surface bordering 

Columbia River and extending far eastward. The difference between 

plateau and mountain range is there simply one of degree of elevation. 

In a similar manner it appears that the upwarps by which the Cascade 

Mountains were uplifted and to which they owe their prominence in 

the vicinity of the international boundary suddenly die out. PL IV, 

A, illustrates the abruptness of this change in topographic character. 

North of the forty-ninth parallel, then, the eastern portion of the Cascades is replaced by the interior plateau. Farther west the western 

portion of the Skagit Mountains might possibly be considered as continued by the Coast Ranges, but the wide area occupied by the Frazer 

delta makes such orographic continuity very doubtful.

This physiographic differentiation of the Cascade Mountains and 

the interior plateau is on the basis simply of a difference in amount 

of uplift. The geologic history of these adjacent provinces may show 

no important differences, and indeed, as far as known, the earlier 

structures appear to extend from the one to the other. Slight differences may develop, however, in the course of the investigation of 

these areas. An example of this is found in the occurrence of an 

Eocene peneplain in the interior plateau region, while in the Cascades 

peneplanation. of Eocene age has not been recognized, and indeed in 

central Washington the Miocene lavas,are known to rest upon a surface possessing considerable relief. The post-Miocene folding and 

the subsequent peneplanation which have been determined for the 

Cascade region appear to have been also epochs in the history of the 

interior plateau. G. M. Dawson recognized both of these periods of 

peneplain development and described the latter period as follows:

Local accumulations of volcanic material, together with the slight folding to 

which the Miocene beds, whether volcanic or otherwise, have been subjected, must

have caused the area of the old Eocene peneplain to be less uniform than before;

and denudation, acting on its projecting parts, began again to reduce these toward 

the general level. This action was long continued and had important effects in 

bringing the interior plateau region again down nearly to the base-level of erosion." ''.'".'.

This surface, which largely represents post-Miocene reduction, was 

uplifted in the latter .part .of Pliocene time; over the Cascade Mountains area the amount of general elevation was about 8,000 feet, but 

north of the .forty-ninth parallel,, judging from published descriptions of the interior plateau, one-half of that amount may be regarded 

as an approximate measure of the mean elevation. During the uplift 

of the interior plateau the antecedent Frazer intrenched itself, just 

as, at the same time, Skagit River maintained its right of way across 

the uplifted Skagit Mountains and the Columbia cut its canyon 

across the broad upwarp of the Cascade Range.

aTrans. Royal Soc. Canada, sec. 4, 1890, p. 16.
U. S. GEOLOGICAL SURVEY BULLETIN NO. 235 PL. IV

A. INTERIOR PLATEAU OF BRITISH COLUMBIA. 

Seen from Bauerman Ridge, Okanogan Mountains, Washington.

B. RUGGED TOPOGRAPHY NEAR FORTY-NINTH PARALLEL, MOUNT BAKER 

MINING DISTRICT, WASHINGTON.

 . v. .: ..'. . . Looking north from Bear Mountain. - -. .= . --.,:-.- , : ...
PHYSIOGRAPHY. .91

GLACIAL SCULPTURE..

Mention lias already been made of the part played by glacial sculpture in the production of the present topography. The great number 

of glacial cirques throughout this boundary region is the most noticeable evidence of such erosion. In the Okanogan Mountains every 

peak has at least one such amphitheater, with its flat debris-covered 

floor often containing a small pond. Some peaks, like Amphitheater 

Peak, have four or five cirques, so that there is only a remnant of 

the originally dome-shaped mountain mass. Only rarely, however, 

has the cutting back of these cirques produced a peak of the Matterhorn type, as the crest is usually long and even, although very narrow. In many cases it ,i.s evident that the vertical jointing of the 

granite has materially assisted the ice in its work. Everywhere the 

indications are that glacial erosion began its attacks on a much less 

rugged topography than that of the present.

The asymmetric character of the sculptural features produced by the

later alpine glaciation impressed the authors in the field, and is evident from an inspection of the contour map of the eastern part of the 

area surveyed. Some of the clearest examples of the phenomena are 

afforded by the U-shaped canyons which drain eastward from the main 

divide into the west fork of the Pasayten. Their northern walls are 

of the greatest simplicity, hardly modified by the small post-Glacial 

torrents that flow down their slopes, but their southern or "shady" 

sides are broken by niches or hanging cirques, obviously of glacial 

origin, and the heads of the main canyons themselves have a northerly 

direction.

The higher peaks, from which the glaciers retreated at a comparatively recent date, show equally an asymmetric form a characteristic 

profile like that of a breaking wave. But the most cursory glance at 

the map reveals the curious fact that while the high cirques generally 

have, as we should naturally expect, an aspect more northerly than 

southerly, the great majority of them face in an easterly^direction, 

and their average or prevailing aspect is about due northeast. The 

prevalence of this tendency can not be accidental, but must have 

resulted from some cause that has obtained throughout the region 

where it is observed.

It in fact appears that the predominance of eastward-facing cirques 

is dependent on at least two concurrent causes. The first of these is 

the prevailing north west-southeast trend of the principal drainage 

lines a feature, it may be remarked in passing, that can hardly be 

without significance, but whose origin the authors are not yet prepared 

to explain. It is evident, however, that the northeastern slopes of the 

ridges, since they receive less sunlight than their southwestern slopes, 

offer more favorable sites for the establishment of alpine glaciers. 

It is believed, therefore, that the peculiarity of the drainage mentioned 

above has been the most important factor in determining the prevailing aspect of the cirques.
.92 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BULL.235.

The most notable examples of cirques that, contrary to the general 

rule, have a westerly outlook, occur along the divides whose directions are transverse to the prevailing trend, notably along those, 

already mentioned, which separate the western tributaries of the 

main branch of the Pasayten and along the crest of the Hozomeen 

Range, where it has a direction almost strictly north and south. This 

north-south portion of the main divide has been carved by the eating 

back of the glaciers from both east and west, but seems to have proceeded rather more actively on the east.

Such irregularity here can hardly be explained as a result of preGlacial topography. It is suggested, therefore, that it may be due to 

the prevalence of west winds, which would have the effect of drifting a 

part of the snowfall across the divide, thus causing a greater accumulation on the east, or leeward, side. This climatic factor mayu be supposed to have acted over the whole region where east-facing cirques 

prevail, its influence being concurrent with that of the prevailing 

trend of the streams.

The peak north of Park Pass, with four cirques containing rockrimmed tarns upon its northeastern flank, also appears to require the 

agency of the climatic cause, though the position of these cirques may 

be in part explained by the proximity of the deep valley of Ashnola 

River on the east, on the slopes of which the snow would accumulate 

more readily than on the. more open and gentle declivity west of the 

mountain.

In the Cascades the glaciers that produced these cirques appear to 

have been of the valley type and to have largely followed the direction of present drainage lines. The largest of these was,, of course, 

the Okanogan Glacier, but smaller ice streams occupied the valleys 

farther west and flowed northward. Remnants of the Pasayten 

Glacier still persist in the mountains at the head of the valley, and 

the shape of the valley shows the former extent of the ice. Upper 

Skagit Valley has also been thoroughly glaciated.

COULEES.

Within the glaciated Okanogau Valley there is a perfect labyrinth 

of deserted stream channels, by which the Similkameen and other 

tributaries united with the Okanogan at various stages of glaciation. 

Willis mentioned these in an early paper/' and clearly stated their 

origin. These channels, which commonly take the name of "coulees," 

were observed from the vicinity of Lake Chelan northwest to the 

international boundary, and in the upper portion of Okanogan Vallej^ 

are so complex that a careful and detailed survey would be necessary 

before a correct interpretation of the drainage changes could be made. 

Mention can here be made, therefore, only of a few of these occur-

«Willis, Bailey, Changes in river courses in Washington Territory chie to glaciation: Bull. 

U. S. Geol. Survey No. 40,1887. ' '
SMITH ANIJ 

CALKINSB] RESOURCES. 93

rences, without any attempt even to outline the interesting history 

which may sometime be worked out for this region.

On the east wall of Okanogan Valley there are several parallel 

gaps steep-sided gashes in the general western slope. These have 

much of the aspect of "displaced blocks" and are striking features, 

one cliff being a precipice of 600 feet. Thirteen miles due west, on 

the opposite side of the valley, however, there is to be seen a similar 

series of. gaps, which plainly represent abandoned channels of Salmon 

Creek. These ^channels were successively occupied and deserted by 

this stream as the advancing Okanogan Glacier pushed the lateral 

drainage higher up the valley wall. There are four of them, the 

floors of which are successively higher, proceeding west, until the deep 

canyon at present occupied by Salmon Creek, which owes its depth 

to post-Glacial erosion, is reached.

Antoine Coulee near the mouth of. the Methow is'a similar feature 

on a much larger scale. It is 10 miles in length, and its floor is 

approximately at the level of the Great Terrace of the Columbia. 

This steep-walled defile, which cuts across the spurs sloping down 

to Columbia River, is believed to be also an abandoned stream channel. Russell" explains it as the fissure behind a displaced block. 

His argument rests upon a supposed greater pre-Glacial depth of the 

Columbia Canyon, whereby the bounding slopes were steeper and 

therefore better fitted for landslides. This supposition is opposed by 

the fact that at the point in question the present flood plain of the 

Columbia is on bed rock even to the water's edge. The thickness of 

the Okanogan Glacier at this point was undoubtedly sufficient to 

divert the Methow drainage along the valley side, where it would have 

started the excavation of such a side channel as Antoine Coulee.

Throughout northern Washington it is apparent that stream erosion may have accomplished tasks that seem incredible, and nowhere 

is its efficiency more forcibly shown than in Okanogan Valley, with 

its intricate system of channels, many of which show glacial action 

to have also contributed to their erosion.

RESOURCES.

AGRICULTURE.

Within the section described in this bulletin, agriculture can not 

be regarded as very important. In Okanogan Valley the meadows at 

the foot of Lake Osoyoos and bordering Similkameen River and H.aipwil Lake furnish limited areas for raising hay. Along the east side 

of Haipwil Lake there are also bench lands where grain and vegetables are cultivated, the soil being fertile, but irrigation necessary, so 

that the scarcity of available water limits the productive area. The

«Russell, I. C., Geology of the Cascade Mountains: Twentieth Ann. Kept. U. S. Geol. Survey, 

pt. 2,19(10, pp. 201-302.
94' CASCADE RANGE WEAK FORTY-NINTH PAEALLEL. [BULL.235.

uplands of Okanogan Valley are used for grazing small bands of 

horses, but the rainfall is insufficient to make this range very valuable.

West of Okanogan Valley several ranches have been taken up on 

the southern slope of Mount Chopaka, but the elevation is too great 

for the land to have much agricultural value. The open grassy slopes 

of this vicinity, however, furnish an excellent summer range for 

cattle, and by opening the trail, through the thickly wooded ravines 

the area available for grazing might be increased, The ridge tops 

and south slopes are covered-with a. luxuriant growth.pf bunch grass 

and other nutritious forage plants, so that; the area east of the forestreserve boundary has.value for grazing purposes. The distance to 

present shipping points, however, detracts from the importance of 

stock raising in this region.

The next agricultural land encountered in the boundary section is 

in Skagit Valley near the mouth of Beaver Creek. A few acres of 

bottom land on the east side of the valley and a natural meadow on 

Beaver Creek have been utilized for raising hay, which is cut and 

baled by hand and packed out. In this vicinity forage is extremely 

scarce, and this hay is the only supply that can be depended upon.

AVest of the Skagifc Mountains the region has the same agricultural 

value as other parts of western Washington. Small ranches have been 

established and fruit raising and dairying are proving profitable. 

Whatcom County will doubtless become more and more important as 

an agricultural district.

FORESTS.

The greater part of this area is included within the Washington 

Forest Reserve. In the Okanogan Mountains and the higher portion 

of the Hozomeen Range the forests are quite open and few trees attain 

a size comparable with those of the forests of west Washington. In 

upper Skagit Valley heavy forests become a characteristic feature of 

the region, and along the lower course of Skagit River the forest trees 

are large and symmetrically developed. Here and east of the Skagit 

Mountains the lumber industry is very important, and the magnificent forests of fir and cedar are rapidly disappearing.

GOLD AND SILVER. 

EASTERN DISTRICTS.

Okanogan Valley has been the scene of mining operations for a 

considerable period. The search for placer gold dates back to the 

time of the original survey of the boundary, when coarse gold was 

found on the Similkanieen, immediately south of the forty-ninth parallel, in quantities that caused much excitement. In later years 

development work has been carried on to a considerable extent in the
GOLJ:> AND SILVER. 95

gold-quartz mines, although there Avas less activity in 1901 than a few 

years before.

The Palmer Mountain tunnel near Loomis had been driven for 

several thousand feet into the greenstone, and had cut twentyeight veins, which follow sheer zones but have well-defined walls. 

The larger of the veins are of quartz, while the smaller ones contain much calcite. The ore minerals are pyrite, chalcopyrite, and 

galena. The Golden Zone mine is located on the west side of the 

Similkameen about 2 miles south of the boundary. The principal 

vein trends N. 20° E., with the hanging wall well defined and persistent. The country rock is granite and the vein material quartz 

and pyrite, with free-milling gold except where galena occurs in association. The highest value in these lead ores is $10, but the average 

gold value is reported as about $25, with silver never exceeding 4 

ounces. The ore is concentrated and amalgamated at the mill immediately below the mine. These two mines are probably fairly representative of this Palmer Mountain district.

In the Okanogan Mountains, from Mount Chopaka west to Pasayten 

River, and along the higher part of the Hozomeen Range, the country 

in the vicinity of the forty-ninth parallel appears quite barren of ore 

deposits. In the lower valley of Pasayteu River the alluvial gravels 

have been thoroughly test-pitted many years since, apparently without promising results. All of the rocks of this region are remarkably 

free from even the common quartz veins.

In the vicinity of Barron, and below on Slate and Ruby creeks, there 

have been mining operations. The rocks here are more closely folded 

and quartz veins become numerous. Several mines are worked at 

Barron, and prospecting is being done throughout the Slate Creek district. Ruby Creek was the scene of great activity in early days, when 

the placers yielded rich returns to the miners, creating a typical rush 

of short duration. Recently hydraulic mining on a large scale was 

attempted at the mouth of Ruby Creek, but the extensive plant, 

which includes a long and expensive flume, has proved a failu're. 

Prospecting has been done on the upper Skagit in the vicinity of 

Lightning Creek, but no success has been reported.

' MOUNT BAKER DISTRICT.

The Mount Baker district .is a more promising field for investigation 

by mining men. Some veins of free-milling gold have been found and 

partly developed. This district is yet young, since prospecting only 

began a few years ago, a condition easily understood in view of the 

difficulties of travel in the Skagit Mountains. The first find of 

importance was made as late as 1897, and the mine that was developed 

in consequence is the only one that could be said to be upon a producing 

basis in 1901. This is the Lone Jack, on the Post-Lambert group of
96 CASCADE RANGE NEAR FORTY-NINTH PARALLEL. [BULL.285.

claims, on the eastern slope of Bear Mountain and near the head of 

the west fork of Silicia, or Slesse, Creek. The vein is 4 to 5 feet, of 

clear-looking, solid quartz, which does not suggest by its general 

appearance any value as a metalliferous vein. The ore, which is both 

free gold and telluride, occurs throughout the vein, although mostly 

Concentrated in a pay streak which lies near the hanging wall, 

or more rarely near the foot wall, or even in the center of the vein. 

Samples from any part of the vein are apt to show minute particles 

of free gold. This vein outcrops for several thousand feet, strikes a 

little west of north, and has an inclination of about 45° to the west, or 

into the mountain. It is a fairly regular fissure vein, including some 

horses of country rock, but having no great variation in width.' The 

rock cut is a schist with lenses and stringers of quartz resembling 

gold veins, which often give the rock a gneissoid appearance. There 

is, however, no evidence of transition between such quartz stringers 

and the large fissure veins.

The value of the Lone Jack ore was reported in 1901 as averaging 

$25 to $30 to the ton. Picked samples from the pay streak have been 

reported as assaying as high as $850, and a 2-ton smelter test is said 

to have netted $450. In 1901 the work of building a stamp mill on 

the creek below the mine was being actively pushed. This will treat 

the ore by amalgamating the free gold and concentrating the tellurides.

Another type of ore deposit is at the Grand Excelsior mine, on 

Wells Creek, about 1 mile southeast of the bridge over the Nooksak. 

Here the work done has been in a mineralized zone in the green conglomerate and chert. Sulphides occur, scattered through the rock, 

and the irregular body of mineralized rock appears to be near the 

surface and approximately parallel with the slope. No definite information could be obtained as to the values in this ore.

Other properties on Tumuieahai Creek and in the vicinity of Hannegan and Twin Lake basins were visited in the course of the rapid 

reconnaissance, but underground development had not reached a 

point where much could be ascertained as to the true value of the 

ore deposits. Gold appears to be the principal ore value, but both 

silver and copper ores are also reported.

The only suggestions that can be made in this report for the guidance of the prospector in this district are those based upon the general 

structural relations of the region. The older rocks of the eastern part 

of the district have been closely folded, crushed, and fissured, and also 

cut by dikes of igneous rocks. The conditions here appear to have 

been more favorable for the introduction and deposition of ore minerals. In the granite, yet farther east, the prospectors report less 

evidence of ore-bearing veins, while below Shuksan, in the western 

part of the district, the rocks have been less metamorphosed and the 

ore. minerals present do not appear to have been concentrated in 

well-defined veins.
RESOURCES. ' . 97 

COAL.

There are productive coal mines in the extreme northwestern part 

of Washington at Cokedale and at Bine Canyon. In Skagit Valley 

near Hamilton there are also coal prospects in beds the age of which, 

according to fossil leaves determined by Dr. F. H. Knowlton, is the 

same as that of the beds at Cokedale, but no development has been 

accomplished at that locality. None of these localities were visited 

in the course of this reconnaissance, and of others that were visited 

none appear sufficiently encouraging to warrant development. Among 

 them was a prospect in the Swank formation in the hills southwest of 

Wenatchee. The country rocks there are shales with a northwesterly 

strike and fairly steep westerly dip. The principal seam shows about 

2 feet of soft, shaly coal of poor quality. It is noteworthy that the 

important coal measures in the Cascade Mountains southwest of this 

locality are not in the Swank formation, but in the younger Roslyn 

formation.

Three prospects in the vicinity of the international boundary were 

visited. One of these is situated in the southeast quarter of sec. 17, 

T. 40 N., R. 5 E., about midway between Sumas and Keese. The 

coal seam strikes north-south with a dip 75°-85° W. The coal is from 

2£ to 3 feet thick and is bright for outcrop coal. It is much crushed, 

with slips cutting across the vein, displacements of this character 

haAdng the effect of increasing the apparent thickness of the seam. 

North and west of this locality green schist is found, so it is probable 

that the coal measures are cut off on that side by faulting.

The second prospect is in the bank of Canyon, or Cowap, Creek, 

about 1 mile from its mouth. The seam, which strikes east-west and 

dips steeply to the north, has a total thickness of about 4 feet, but 

contains much bony material.

South of the Nooksak, in a canyon emptying nearly opposite Cowap 

Creek, at an elevation of about 3,000 feet, there is a third coal prospect, to which a good trail has been constructed from the road in the 

valley. The country rocks are shales, sandstones, and conglomerates, 

presumably of Tertiary age, striking northwest and dipping 45° northeast. They are underlain a short distance to the south by metamorphosed sediments of much greater age. The coal vein is nearly 4 feet 

thick, but is divided by a thin seam of shale. The coal is soft and 

much broken and slickensided, as though by shearing and squeezing, 

a fact which suggests that the contact with the older rocks may be a 

fault plane.

Bull. 235 04 7

INDEX.

Page. 

Acidic dike rocks, description of......... 74-76

Artamellite, suggestion of name of....... 63

Agriculture in the Cascades, comparative

unimportance of.-..--.....------- 93-94

in Skagit Valley....................... 94

Alkali in igneous rocks of Cascades, general low content of................ 83

Amphitheater Peak, character of........ 88

view of.................................. 88

Amphitheaters, occurrence and forms of 91-92 

Andesi tes, description of ................. 56-60

occurrence and character of.......... 31

Antoine Coulee, extent and origin of..... 93

glacial deposits in..................... 38

granite-porphyries in................. 75

schist and gneiss in.................... 22

Aplites, occurrence and character of..... 76

Austin Pass, rocks near................... 27,57

Baker, Mount, elevation and location of. 17 

formation and age of .......:.....--.. 35

lavas of, character of..-........-.----. 35

relative age of..................... 86

N pre-Cretaceous rocks near............ 21

pyroxene-andesite in. ......_..._...... 57-59

district of. (See Mount Baker dis- i

trict.) 

Barron, Wash., fossils near............... 28

mining operations near............... 95

rocks near .......................... 29,75,79

Basalt, occurrence and character of. 33-34,60-61 

Basaltic angite-andesite, occurrence and

character of .-....-.'.........-..... 59

Batholiths in Okanogan Mountains, occurrence and importance of...... 84

Bauerman, H., cited on Cascade Mountains ............................... . 14

cited on geology of Washington...... 12

Bauerman Ridge,elevations on........... 13

view from ............................. 90

Bear Mountain, fossils at...............:. 25

.view from ............................. 87,90

Bighorn Peak, elevation of............... 14

soda-syenite near..,................... 76

Biotite-granite, occurrence and character

of................................ 47,65-66

Biotite - muscovite - granite, occurrence

and character of................ 48,62-64

Blackwelder, Eliot, moraine traced by... 36 

Blue Lake, Tertiary beds near............ 33

Brogger, W. C., reference to.............. 63

Cache Creek series, correlation and character of ............................. 22-23

occurrence of.......................... 32-33

Page. 

Calkins, F. C., cited on Yakirna basalt.... ' 60

part of report prepared by........... 11

work of ..........................^..^.. 11

Canadian boundary party, work of ...... 20

Canyon Creek, coal prospects near....... 97

fossils on and near .................... 27

rocks at head of....................... 29

Canyons, formation of .................... 90

Cascade Range, climatic differences on 

slopes of............................ 18

composition of....-...---....-....---.. 79-80

description of.......................... 13-17

formation and age of.................. 86

general featuresof.................... 84

geology of northern partof.........j. 20-92

glaciationin........................ 15,41-43

map of ................................. 21

nor them termination of.............. 13

physiographic subdivisions of........ 88^89

reconnaissance across, work of....--. 11-12

route followed ...................... 12

relation of, to interior plateau........ 89-90

to Coast ranges.................... 89-90

subdivisions of ........................ 14

topographic features antedating formation of..--.-.-...-.-...-........ 86

true, definition of ..................... 14

western foothills of, Eocene beds in.. 30,34 

western side of, glacial deposits on .. 42 

Cathedral Peak, biotite-muscovite-granite near ............................ 48

character of..........'................. 88

elevation of............................ 14

pass near............................... 19

view of................................. 88

Chelan Lake, granodiorite near......._ 45

Chilliwhack Lake, formation of, by moraine............................... 41

Chopaka, Mount, location and elevationof................................... 13,14

ranches near .......................... 94

rocksof................................ 47

serpentines and pyroxenites in....... 73

uralitic gabbro in ..................... 72-73

Cirques, occurrence and character of..-. 91 92 

Climate of northern Washington, character of.............:..-........... 17-19

Clover, Wash., rocks near....... 22,34,45-46,56

Coal, occurrence and descriptions of.. 30,34,97 

Coast system of British Columbia, relation of, to Cascade Range......... 89

Columbia River Valley, glaciation in .... 35-41

marginal differentiation in........... '80

99
100 INDEX.

Page.

Columbia River Valley, Pleistocene deposits in............................ 35-41

rocks in....................... 21-28,32,44,67

Contact phenomena, occurrences of ..... 80-81

Coulees, occurrence, extent, and character of ............................ 92-93

Cowass Creek. (.See Canyon Creek.) 

Cretaqeous conglomerate on Hozomeen

Range, view of .................... 33

Cretaceous strata, character and occurrence of............................ 28-30

fossils in ............................... 28

Ouster, H., expedition of ................. 16

Ouster Ridge, name proposed for ........ 16

Dacite, occurrence and character of..... 33,56

Daly, R. A., cited on Chilli whack Lake.. 41 

cited on granitoid rocks .............. 50

cited on structure of Mount Baker

district............................. 85

cited on "tandem cirques"........... 16

quoted on formation of the Cascades. 86 

quoted on northern Cascades......... 14

' survey by.............................. 25

Dawson, Ot. M., cited on Cache Creek

series.......:..;.................... 22

cited on orography........'............ 89

cited on peneplain development-..... 80

Dawson, J. W., cited on name Similkameen............................... 28-29

Dawson, W. L., cited on glacial geology

of Washington ................. 36,42

cited on glacial erratics............... 37

quoted on origin of gravel deposits... 39 

Doming, Wash.; Tertiary sandstone bluff

near:............................... 42

Devil Creek, gorge on..................... 15

structure near......................... 85

Diabase, occurrence and character of.... 46,79

Dike rocks, occurrence of .................. 48,49

Diller, J. S., mention of ................... 27

Diorite, description of..................... 69-71

occurrence of..2.............-...'....... 48,78

Diorite-porphyries, occurrence and character of ............................ 77

Dioritic rocks, occurrence and character of............................... 45-46

Downwarps in Cascade Range, indicationsof...'.......................... 88

Drainage, direction of .................... 91

features of. '.. .......................... 17

Entiat,Great Terrace near ............... 40

.rocks near .............................. 45,75

Eocene beds, occurrence of............... 30,34

Erosion, influence of ................... 83-88,93

glacial, evidences of................... 91-92

Fish Lake, quartz-diorite near ........... 46

Fort Hope trail, description of ........... 20

trip over ........................ ....... 12

Forests in northern Cascades, importance of............................ 94

Fossils, occurrence of........... 24,25,27,28,34

Fuller, W. H., fossils collected by ........ 27

Gabbro, occurrence and character of. 46,71-73 

Garrey, George H., moraine traced by... 36 

Geography of the Cascade region......... 12-19

Geology of northern Cascades............ 20-92

Ptige.

Gibbs, George, cited on Cascade Range... 13 

cited on geography of northwestern

boundary.......................... 12

Glacial deposits, occurrence and character of -.._--...----....-...- -..--.- 35-42

Glacial sculpture, features of............. 91-92

Glaciation, extent of...................... 92

traces of ...................... 15-17,35-41,92

Glaciers, present occurrence of .......... 17,92

Glaucophane - schists, occurrence and

character of....................... 54

Gneiss, occurrence of..................... 22

Gold in Cascades, occurrence of .......... 94-97

Golden Zone mine, nature of vein in ..... 95

Grand Excelsior mine, character of ore

deposit in .......................... 96

Granite, occurrence and character of.... 43-46,

50,62-66 

graphic, occurrence of.-...--........- 75

Granite Mountain, rocks on ........ 51,71,75,78

marginal differentiation near ........ 80

.Granite-porphyries, occurrence and character of -...........-....'........... 75

Granitic rocks, belt of .................... 47

extent and charactar of............... 50

zone of, eastern boundary of ......... 49-50

Granodiorite, acidic type of .............. 66-67

basic type of-......--....--.-----...-.. 67-69

megascopic features of................ 44

occurrence and character of.......... 45,

47-48,51,66-69 

Granophyre, occurrence and character

of.-.......----..---.......-------..- 74

Gravel deposits, occurrence of, in Pasayten Valley.......................... 42

occurrence and origin of........ 39-40,42-43

Grazing in Okanogan Valley, extent of.. 94 

Great Terrace, description of............. 40

elevation of--..-..-.--.....-.....-....- 40

location and description of ........... 37-41

origin of . ^............................. 41

Haipwil Lake, agriculture near __..____._ 93

granodiorite west of .................. 48

Hamilton, Wash., alluvial plain at....... 4!J

coal near............................... 34,97

rocks near .......:..................... 21,34

Hannegan Pass, volcanics near._._._...,.. 27

Hardan, Wash. (See Maple Falls.)

Hay in Skagit Valley, production of .... 94

Hidden Lakes, rocks near .......... 33,56,59,60

Hornblende-porphyries, character and

occurrence of..........--..-.---... 77

Hornblende- pyroxene - andesi te, occur-

' rence' and character of......... 33,56-«57

Horseshoe, The, rocks of......... 47-48,65,70,77

Hozomeen, Mount, eleva-tion of........... ' 16

Hozomeen Range, climatic conditions

of .................................. 18

Cretaceous conglomerate in, view of. 33 

definition of ........................... 14

description of..'........................ 15

folding on...............'............... 84

forests on, importance of .............. 94

rocks on................................ 49

spurs on.. ................................ 88

upwarp represented by............... 88-89
INDEX. 101

Page. 

Hypabyssal rocks, description of......... 78-79

distribution and classification of..... 73-74

table of................-................ 74

Hypersthene-basalt, occurrence and character of............................ 34,60

Ice sheet, elevation of..................... 88,41

Iddings, J. P., cited on eruptive rocks.... 70

Igneous rocks, character and form of occurrence of ........................ 43

description of ................ 21,31-34,43-84

origin and extent of................... 83

relationships and character of........ 81,83

(See also Plutonic rocks.) 

Interior Plateau, relation of Cascade

Range and......................... 89-90

view of................. --.....-.-.--.-- 90

Intrusive rocks, classification of.......... 43-44

description of.......................... 43-51

> occurrence and character of.... 44-45,47-51

Iron, occurrence of........................ 25

Jacks Mountain, elevation of............. 16

sedimentary and volcanic rocks in... 23 

Keese, Wash., coal prospects near........ 97

rocks near ............................. 34

' gravel terraces near..................: 42

Knapp Coulee, granodiorite near......... 45

Knowlton, F. H., cited on Tertiary fossils. 34 

Lamprophyric dike rocks, description of. 76-79 

Landes, Henry, fossils collected by ...... 34

Lava, occurrence and character of...:... 52-53 

near Mount Baker. (See Mount

Baker lava.) 

Lightning Creek, structure near......... 85

Lindgren, W., cited on granodiorites.... 67

Lone Jack mine, description of........... 95-96

Loomis, Wash., gold mines near.......... 95

rocks near........... 22-23,32,46-47,52,69,76

Lowland surface, former, identification of 87-88 

Lumber industry, importance of......... 94

Mamie Pass, rocks near................ 50,70,78

Maple Falls, Wash.,gravel terraces near. 42 

rocks near ............................. 26

Marblemount, Wash., rocks near ........ 25

Marginal differentiation, evidences of... 80-81 

Mesozoic rocks, supposed occurrence of . 27 

Metabasalt, occurrence and character of. 61 

Metamorphic rocks, occurrence and character of............................ 52-53

Methow River, granodiorite near ........ 45

Mining district, Mount Baker, location of. 17 

Miocene lavas in central Washington,

position of ................I........ 90

Moraines, occurrence of.......:........ 36,37,41

Mount Baker. (See Baker, Mount.)

Mount Baker district, gold mines in ..... 95-96

rocks in........................... 25-28,66-67

structure in................. ......'...... 85

Mount Baker lava, character and occurrence of----------.---....-J........ 57-59

Nokomokeen, Mount. (See Jacks Mountain.) 

Nooksak River, rocks near ................ 58-59

coal prospects south of................ 97

gravel terraces along ................. 42

rocks in canyon of.................'.... 27

structure along........................ 85

Page. 

Nooksak River, North Fork of, descrip-

 tion of..........-....'--------....... 17

Nooksak Valley, rocks in ................. 34

Northwest boundary, geologic reconnaissance of, parties assigned to ...... 11

geologic reconnaissance of, route of.. 12 

Okanogan Glacier,extentandthicknessof 36-38 

Okanogan Mountains, climate of......... 18

description of.......................... 14-15

elevation of............................ 88

forests on, importance o f ............. 94

rocks in.....................:.... 47-48,65-67

upwarp represented by............... 88-89

views in................................ 88

Okanogan River, terraces on ............. 13

Okanogan Valley, agriculture in......... 93-94

description of......---.-...........-..- 13

elevations in................1.......... 13.

erosion in.............................. 93

glaciationin........................... 35-41

gold and silver in...................... 94

Pleistocene deposits in ................ 85-41

rocks ill................. 21 -22,130-32,45,63-64

Olivine-hornblende-gabbro, occurrence

and character of .................. 71-72

Orondo, Wash., rocks near ............ 74,77,79

Oroville, rocks near.....:................. 22,32

Osoyoos Lake, agriculture near.......... 93

country near, aspect of ............... 18

elevation of......-...-...-.----........ 13

reconnaissance begun at.............. 12

rocks near................:...... 33,46,65-66

Paleozoic rocks, supposed occurrence of. 26-27 

Palmer Lake, rocks near.................. 46,52

Palmer Mountain, gold-quartz mine on.. 95 

rocks near............................. 23,72

Park Pass, cirques near. ................... 92

description of.......................... 19

rocks near .......................... 48,75,79

Fasayten formation, character and

thickness of........................ 29-30

folds in..............................:.. 84

occurrence of.......................... 28

origin of name of......'......--........ 28-29

Pasayten River, rocks near............... 29

Pasayten Valley, downwarp represented

by......--....-.------------.-.-.-. 88-89

elevation of............................ 15

glacial debris in ....................... 41

glaciation in........................... 92

gravel deposits in .....i............... 42

Pegmatites, occurrence and character of 75-76 

Peneplain, existence of................ 86-88,90

extent of............................... 87

Peridotite, occurrence and character of. 79 

Peters Canyon, gravel deposits in, origin

of ................................... 39-40

Petrography of Cascade Mountains, conclusions on......................... 79-83

discussion of.......-----------......... 51-79

Physiography of Cascades, description of 85-93 

Pirsson, L. V., cited on geology of Little

Belt Mountains.................... 81

Plateau west from Mount Baker, charac-

 ter of..-'--......------..------------ 86

Pleistocene formations, lava occurring in. 35
102 INDEX.

Page. 

Pleistocene glacial and stream deposits,

classification of.................... 36

Pliocene uplift, elevation of.............. 90

Plutonic rocks, description of............ 61-73

distribution and classification of..... 61-62

quantitative table of essential minerals of............................. 82

relative importance of................ 62

tableof- - -. - - 61-62 

(See also Igneous rocks.) 

Pre-Cretaceous rocks, occurrence and

character of ...._.._ . ..' 21-27

Puget Sound basin, gravel deposits in ... 43 

Pyroxene-andesite, occurrence and character of ................ 33-34,57-59,60,73

Quartz-augite-mica-diorite, description

of................................... 70-71

Quartz-diorite, occurrence and character

of................................ 45-46,49

Quartz-mica-diorites, description of ..... 69-70

Quartz-yorphyry, occurrence and characterof............_................ 75

Quartz-pyroxene-mica-diorite, description of.............................. 70

Quaternary formations, description of... 34-42 

glacial and stream deposits of........ 35-42

Rainier, Mount, lavas of.................. 59

Remmel, Mount, diorite-porphyries in... 77 

elevation of............................ 14

graphic granite near.................. 75

type of biotite-muscovite-granitein.. 62-63 

Rhyolite, description of................... 55-56

occurrence of.......................... 31,34

Riverside, Wash., gneiss near............. 22

Roads and trails in northern Washington,

account of.......................... 19-20

Rosenbusch, H., classification of lamprophy r ic rocks by.................... 76

mention of -...-................'........ 83

Rosiwal, A., cited on method of analysis. 69 

Roslyn formation, occurrence of coal in. 97 

Ruby Creek, gold mining on.............. 95

gravel terraces in gorge of............ 42

rocks on... ....... ....... 28-29,49-50,69-70,73

Russell, I. C., cited on accumulations in

Antoine Coulee.................... 37

cited on age of Slate Creek rocks..... 28

.cited on dikes near Barren............

cited on geology of Cascade Mountains ---..--......--................ 11,93

cited on glacial geology of Washington . . ................__.. ._ 36

 cited on gravel deposits in Peters

Canyon ...:........................ 39

cited on name of Pasayten formation ................................. 28-29

cited on Okanogan Glacier ........... 36,39

cited on Ruby Creek serpentine...... 49

diabase collected by........;.......... 79

quoted on fossils from Barron and

Crater Pass........................ 28

quoted on origin of Columbia terraces . ... ..................... 38,39

Ruth Creek, rocks in....... .__......... 26

Salisbury, R. D., cited on glacial geology

of Washington.....!............... 36

Page.

Salisbury, R. D., cited on Columbia terraces............................... 38

quoted on extent of terminal moraine. 36-37 

Salmon Creek, previous channels of...... 93

Sauk, Wash., rocks near....._- _-..... 25

Sauk Mountain, rocks of._._....-...--.--- 25,60

Sauk River, rocks along and near........ 24-25

Saxonite, occurrence and character of... 73 

Sciiists, occurrence and character of... 22,53-54 

Sculpture, glacial,' description of......... 91-92

Sedimentary rocks, occurrence of...... i. 20-31

Serpentines, occurrence and character of. 49,73 

Shuksan, Mount, granite near............ 49

Shuksau, Wash., gravel terrace near .... 42

rocks near............................. 27

Silicia Creek, granite near, character of. 50 

Silver, occurrence of...................... 94-97

Similkanieen formation. (See Pasayten

formation.) 

Similkanieen River, agriculture near.... D3

bend of, elevations in.................. 13

description of.......................... 16,17

former channels of.................... 92

Tertiary sediments on, view of....... 33

terraceson ............................. 13

Similkanieen Valley.gold in.............. 94

rocks in................................ 33

Skagit-Cutnberland mine, fossils at...... 34

Skagit Mountains, location and general

features of......................... 11-17

upwarp represented by.. . ..- 88-89 

Skagit River, description of.............. 17

Skagit 'River basin, rocks in.............. 21-22

Skagit Valley,-agriculture in............. 94

coal in.................................. 97

description of.......................... 16

downwarp in.......................... 88-89

elevation of............................ 15

forests in, importance of.............. 94

glaciation in........................... 92

gravel deposits in ..................... 42

rocks in.................... 24,50,53,54,60,67

uplift in................................ 87

Slate Creek, rocks on __....._.._...._..... 28,29

structure near......................... 85

Slate Creek district, pi-ospecting in ...... 95

Smith,.G. 0., cited on rocks of Mount'

Rainier __..........-.. .......... 59

cited on Swatik formation ............ 30

cited on Yakima basalt ............... 32,60

part of report prepared by ........... 11

reconnaissance in Cascades by........ 24

work in charge of ..................... 11

Smith, G. O., and Willis, Bailey, cited on

geology of Washington ........... 87

cited on Puget Sound gravels --...... 43

Soda-rhyolite, occurrence and character

of.'.-....................-... ..... 55-56

Soda-syenite, occurrence and character

of.-....--..-......-....--,.. --- 76

Squantl Falls, view of Tertiary sediments

near................................ 29

Stanton, T. W., quoted on fossils from

Canyon Creek ..................... 27

Stream erosion in northern Washington,

importance of ..................... 93
INDEX. 103

Page. 

Stream deposits, occurrence and features

of.................................... 35-42

Structure, discussion of................... 84-85

Sumas Prairie, elevation of..-......;..... 17

Swauk formation, character of........... 30-31

Synclinoriuin in northern Cascades, evidence of............................. 84

 Table Mountain, geologic character of... 32 

"Tandem cirques," occurrence of........ 16

Terraces in Columbia Canyon, description of.............................. 38-41

Tertiary sediments, description of....... 30-34

on Similkameen River, view of... 33 

Three Fools Creek, rocks on.............. 29

structure near..................... 85

view near.......................... 33

Toats Coulee Creek, gravel deposits east

of................................... 42

Topography of the Cascades.............. 12-17

remnants of old........................ 86-88

Trails in northern Washington, account

of................................... 19-20

Tummeahai Creek, mining properties on. 96 

Tummeahai Lake, rocks near ............ . 26

Twin Lakes; fossilsat........._..'......... 25

Twin Lakes Pass,rocksqear.............. 26

Ultrabasic rocks, description of.......... 73

Uplift in northern Cascades, elevation

and extent of...................... 87T88

results from........................... 87-88

Upwarps in Cascade Range, indications

of................................... 88

Page.

Uralitic gabbro, occurrence and character of............................ 72-73

Volcanic rocks, description of............ 54-61

distribution and classification of ..... 54

occurrence and characterof.......... 23,

25,27-28,HI,35 

table of ................................ 55

Washington, northern, climate of........ 17-19

resources of.:.......................... 93-97

roads and trails i»...................... 19-20

vegetation in ..........................' 18

Washington Forest Reserve, area included in...................'........ 94

Wenatchee, Wash., coal near............. 97

rocks near ...............;....... 30,31,55-57

Whatcom County, agricultural importance of............................ 04

Whitestone Hills, character of ....;....'.. 32

Wickersham, rocks near.............I.... 27

Willis, Bailey, cited on Columbia terraces..:............................. 38

cited on glaciers in northern Washi ng ton.--.....-.....--..-......-.... 30 -

cited on river courses in Washington. 92 

downwarp observed by ............... 89

reconnaissance in Cascades by........ 24

survey by...._...................... 12

Willis, Bailey, and Smith, G. O.,cited on

geology of Washington .'.......... 87

cited on Puget Sound gravels......... 43

Yakima basalt, occurrence and character

of.......I...................'.. 31-32,00-01

0