DE.PAS'TMEJTT OP THE INTEBIOE

BULLETIN

OF THE

UNITED STATES

GEOLOGICAL SURVEY

USTo.- 89

WASHINGTON"

GOVERNMENT PRINTING OIT1CE

1898

UNITED STATES GEOLOGICAL SURVEY

CHARLES D. WALCOTT. DJLKECTOK

SOME LAYA FLOWS

WESTERN SLOPE OF THE SIERRA NEVADA, CALIFORNIA

F. LESLIE RANSOME

WASHINGTON

GOVERNMENT PRINTING OFFICE

1898

CONTENTS.

Page.

Letter of transmittal ....................................................... 7

In trod action.................. .................. ............................ 9

General outline of the physiography of the region........................... 10

The occurrence and distribution of the lavas (latites)........................ 14

Petrography of the latites and of the other volcanic roclcs associated with them. 27

The Table Mountain flow ............................................... 28

The biotite-augite-latite ................................................ 37

The Dardanelle flow .................................................... 46

Associated volcanic rocks ............................................... 52

Chemical composition of the Sierra Nevada latites........................... 57

Classification of the latites.................................................. 59

The evidence of the lava flows as regards erogenic movements............... 69

Summary.........'.......................................................... 71

Index ...................................................................... 73

ILLUSTRATIONS.

PLATE I. Diagram showing the position of the area embraced by the map. 9 

II. Map of a portion of the region drained by the Stanislaus Eiver, 

showing the distribution of the Jatites and other Neocene lavas 

and tufts ................................... 1.................. 12

III. The Dardanelles from the west, showing the hummocky granitic 

surface in the foreground and the crest of the Sierra Nevada in 

the distance ................................................. 14

IV. Table Mountain flow resting nuconformably upon beds of fragmental andesito, south of Squaw Hollow..................... 20

V. Contact between the massive latito of the Table Mountain flow 

and the underlying andesitic breccia, 1£ miles east of Clover 

Meadow .......................................:............. 22

VI. Andesitic conglomerate underlying Table Mountain flow, ! £ miles

east of Clover Meadow....................................... 24

VII. View of bluff which terminates the ridge about 2 miles oast of 

Clover Meadow, showing the stratification of the andesitic 

beds.......................................................... 26

VIII. Spheroidal facies of augite-latite of the Table Mountain flow.... 28

I.. Columnar facies of augite-latite of the Table Mountain flow..... 30

X. VieAv of the Dardanelles from a high point to the south, looking

over the canyon.of the Middle Stanislaus River............... 32

XI. Microsectious of latites (seinidiagrammatic).................... 34

LETTER OF TRANSMITTAL.

DEPARTMENT OF THE INTERIOR, 

UNITED STATES GEOLOGICAL SURVEY,

Washington, D. 0., June 19, 1897.

SIR: I have the honor to transmit herewith an illustrated paper by 

Dr. F. L. Kansome on some lavas from California that are regarded as 

intermediate between trachytes and andesites. It may be noted that 

these rocks occupy the same position among the effusives that certain 

of the rocks called monzonite by Brogger do among the granolites. 

It is recommended that the paper be published as a bulletin.

Very respectfully, yours,

H. W. TURNER,

Geologist. 

Hon. CHARLES D. WALCOTT,

Director United States Geological Survey.

1

U. S. GEOLOGICAL SURVEY BULLETIN NO. 89 PL. I

DIAGRAM SHOWING THE POSITION OF THE AREA EMBRACED BY THE MAP (PL. II).
SOME LAVA FLOWS OF THE WESTERN SLOPE OF THE 

SIERRA NEVADA, CALIFORNIA.

BY *!F. LESLIE EANSOME.

INTRODUCTION.

The field relationships of the rocks described in the folio wing'paper 

were studied during the summers of 1895 and 1896, while I was engaged 

in geologically mapping portions of the Sonora and Big Trees quadrangles, under the direction of Mr. H. W. Turner. It was seen that this 

particular set of lavas offered a promising field for more detailed work 

than could be given to the region as a whole, and Mr. Turner kindly 

suggested that I should undertake their investigation as a special problem, to be carried along in conjunction with the regular area! work of 

the quadrangles. It was found that, in addition to the andesitic tuffs 

and breccias (designated upon the completed folios of the Gold Belt of 

California "Neocene andesite-tuff," or "Neocene andesite"), which are 

so widely and monotonously developed over the broad western slope of 

the Sierra Nevada, there occurs within the district studied another series 

of lavas in the form of massive flows, of much more limited distribution. They are in some cases closely associated with the breccias and 

tuffs, but are always readily recognized by their prevailingly massive 

character and by certain very distinctive lithological features. Taken 

as a whole, they form a series of superimposed flows, extending in a 

southwest direction from some as yet unknown source near the crest of 

the range in Alpine County down to the little village of Knights Ferry, 

in Stanislaus County, on the border of the Great Valley a distance of 

more than 60 miles as the crow flies. Only one of the flows is known 

to have extended the whole distance, and they have all suffered considerable dissection through the very incisive gashing of the present 

streams, but in a general way the line of flow maybe said to follow the 

course of the Stanislaus Eiver. These flows were poured out within 

the period of eruptive activity, during which the andesitic breccias and 

tuffs were spread for hundreds of square miles over the western slope 

of the Sierra; but their eruption was immediately preceded by an interval of sharp erosion, which cut out the channels down which they flowed

9
10 LAVA FLOWS OF THE SIERRA NEVADA. [BULL. 89.

toward the valley. Subsequently they were again partly covered by 

fresh andesitic breccia, especially in the higher portions of the range.

The distinctive chemical feature of these rocks is a rather high percentage of total alkalies, with the potash somewhat in excess of the 

soda. Chemically they stand between typical andesites and typical 

trachytes, and belong to a general chemical group of the effusive rocks 

which it seems necessary to classify under a new name. Without 

anticipation of a discussion which has its proper place after the rocks 

themselves have been described, the name latite (derived from the 

Italian province of Latium or Latia, where rocks closely related to those 

described in the present paper occur abundantly), may be considered 

for the present as used merely to indicate^the group of lavas which 

form the subject of the present paper, for the purpose of avoiding confusion with the ordinary clastic andesites abundant in the same field.

The laboratory work embodied in the preparation of this paper was 

carried on in the petrographical laboratory of Harvard University, and 

my thanks are due to Professor Wolff for the excellent facilities there 

enjoyed. I am also indebted to Mr. Turner not only for the original 

permission to undertake the work, but for generously aiding it in many 

ways and for furnishing field notes of such occurrences of the latites 

as fell within his own portions of the general area.

GENERAL OUTLINE OF THE PHYSIOGRAPHY OF THE

REGION.

The accompanying map (PI. II) embraces a rectangular strip of conntry 03 miles in length and 14.5 miles in width, with its longer dimension 

lying very nearly northeast and southwest. It includes portions of the 

Oakdale, Sonora, Jackson, Big Trees, Dardanelles, and Pyramid Peak 

atlas sheets, and the general position of the district covered is indicated 

in the annexed diagram (PL I). Considerably more than half the area 

lies within the Big Trees sheet. The extreme southwestern portion, 

lying west of longitude 120° 30' and south of latitude 38°, is from the 

northeast corner of the unfinished Oakdale sheet. The topography is 

here only partly indicated, and the areas of latite are drawn with 

approximate outlines subject to revision when the region is examined 

in detail with a finished topographical map. A similar explanation 

should also be made with regard to the corner of the map lying east of 

longitude 120°, which is a part of the Dardanelles sheet. The work in 

this area was limited to a rapid reconnaissance, before the completion 

of the topographical base, and the areas of Neocene lavas will require 

slight modifications and considerable additions when the areal geology 

of the Dardanelles quadrangle is worked out in full.

The elevations on the map range from a general altitude of about 500 

feet, near Knights Ferry, to 9,529 feet, on the summit of Dardanelle 

Cone, in Alpine County, corresponding to an average grade of 150 feet 

per mile for this portion of the Sierra slope. As a whole, this area is
RANSOME.] PHYSIOGRAPHY OF THE REGION. 11

practically destitute of alluvial valley bottoms, and is drained by 

streams of torrential character. It is traversed from end to end by 

the comparatively young consequent Stanislaus Eiver, with its two 

principal branches, the Xorth and the Middle forks, and may be 

regarded as a thoroughly typical transverse strip of the great tilted 

and dissected peneplain which forms the western slope of the Sierra 

Nevada. The rocks upon which this somewhat uneven peneplain has 

been carved are those of the so-called "Bed-rock series" of the Gold 

Belt folios, and are of Juratrias and earlier age. In the foothill region 

they consist of closely compressed clay slates, schists, limestones, 

quartzites, and various igneous rocks, while in the higher portions of 

the slope gneissoidal and granitic rocks prevail.

Toward the end of the base-leveling pro'cess, which, as shown by 

Diller ] and Lindgren 2 for other portions of the Sierra, lasted at least 

into the Mioceue, the series of volcanic eruptions began which continued through the Pliocene, and which ended by covering' the old Surface far and wide with a blanket of clastic andesilic material in the 

form of breccias, rolled gravels, and fine tuffs. At the same time 

began the differential elevation which has given the peneplain its 

present slope of about two degrees to the southwest. According to 

Lindgren, :! there is still recognizable a peneplain of Cretaceous age in 

the common altitude of many of the higher peaks of the middle Sierra, 

but no survival of such an intermediate stage of base-leveling has 

been detected in this region of the Stanislaus drainage.

The old surface revealed to-day by the stripping off of a great part of 

its andesitic cover is by no means a perfectly even one. If the sharp 

V-shaped canyons of post-Tertiary date were all filled up, and the remnants of the Tertiary volcanic cover quite removed, there would still 

remain a surface of gentle relief surmounted by occasional monadnocks. 

On the whole, though, it would be a topography of greatly subdued 

relief when contrasted with the possibilities for alpine types of form 

suggested by the nearly vertical schistose rocks and batholitbic plutonic masses out of which it was carved.

The peneplain character has not been equally well preserved in all 

portions of the region. In the foothill districts it is recognizable only 

in a very general way, erosion having largely obliterated the old surface or obscured it by the etching out of later and local lowlands. The 

reason for this is threefold: The foothill regions are not only composed 

of belts of highly tilted heterogeneous rocks, originally unfavorable to 

the production of an ideal peneplain, but in addition to this they were 

probably never so thoroughly covered by the coarse andesitic breccias 

as were the higher portions of the slope. Moreover, the lack of homogeneity in the underlying rocks has led to the rapid development in 

Pleistocene time of small subsequent streams along belts of weaker

1 Topographical revolution 011 the Pacific coast: Fourteenth Ann. Kept.TJ. S. Geol. Survey, Part IT, 

1894, pp. 410-421.

* Age of the auriferous-gravels of the Sierra Nevada: Jour. Geol., Vol. IV, 1896, pp. 893 and 898. 

8 Loc. cit., p. 897.
12 LAVA FLOWS OP THE SIERRA NEVADA. [BULL. 89.

rocks, and thereby effected a far more widespread degradation of the 

surface than in the higher region presently to be described, where the 

underlying rocks are not only more homogeneous, but have been more 

thoroughly protected from attack.

Nowhere within the area of the map is the old peneplain character 

better preserved than in the region included between the North Fork 

and the Middle Fork of the Stanislaus Eiver. All the higher ridges 

are capped by audesitic breccia, and as a rule present flat, even tops, 

with a very gently ascending grade to the northeast. As these ridge 

tops are generally bare, or covered only with patches of low-growing 

shrubs and scattered trees, they are the natural routes of travel 

through the district and are followed by the sheep and cattle herders, 

who make use of the higher mountain meadows during the summer 

months. In.contrast with the bare or open character of the ridges, the 

intervening slopes and canyons are generally heavily forested with 

noble trees, including the famous "mammoth trees " (Sequoia gigantea), 

the more graceful and scarcely less majestic u sugar pine" (Pinus lambertiana), and the massive "yellow pine" (Pinusponder'osa).

Following one of the ridges the traveler may ride for hours on a 

scarcely perceptible grade toward the northeast, with a wide prospect 

over the treetops on either hand and a view of similar ridges in the 

distance. But if, as Whitney says, speaking of the mining regions of 

the Sierra, " he turn and attempt to make his way across the country, 

in a line parallel with the crest of the range, he will discover that this 

apparent plain is cut into by the gprges or canyons in which the present 

rivers run in a most extraordinary manner; he will find it several hours' 

work to descend into one of these and rise again to the general level 

on the other side, even if he be assisted by a well-beaten trail." 1

The drainage of the middle portion of the slope differs from that of 

the foothill region in the absence or insignificance of purely subsequent 

Streams. The larger tributaries show a tendency to flow straight down 

tke tilted peneplain, entering the main trunk streams obliquely, and 

frequently after running for a long distance nearly parallel with them, 

as in the case of Beaver Creek and the North Fork of the Stanislaus, 

the former being at one point apparently in imminent danger of capture by the latter. As a result of this consequent system of drainage, 

the deep canyon of the Middle Fork receives practically no tributaries 

from its southern side, the brink of its canyon wall being the divide. 

The North Fork shows a similar poverty in tributaries on its northwest 

side, streams frequently heading close up to the brink of its gorge, but 

generally diverging from it at a small angle toward the west and running finally into the Mokelumne Eiver to the northwest. In other 

words, the general direction of consequent flow roughly bisects the 

angle made by the two main forks of the Stanislaus. The whole area 

is characterized by very active but concentrated erosion. The larger

1 Auriferous Gravels of the Sierra Nevada, Cambridge, 1880, pp. 63-64.
U.S.GEOLOGICAL SURVEY. BULLETIN N9 89. PL.I

MAP

OF A PORTION OF THE REGION DRAINED BY THE

STANISLAUS RIVER

CALIFORNIA

SHOWING THE DISTRIBUTION OF THE LATITES

AND OF THE ASSOCIATED NEOCENE VOLCANIC ROCKS

BY F.L. RAN SOME

1898

Scale 125,000

2 *

Contour Interval 50O feet

LEGEND

Khyolitf and rhyolitic tuff 

I Biotile-augite-latite 

Augite -latite 

Andesitic breccias and tiilTs 

Olivjne -basalt

GRADE PROFILES OF THE NEOCENE AND PRESENT eooo

CHANNELS OF THE STANISLAUS RIVER 

VERTICAL SCALE TWICE HORIZONTAL
KANSOME.] PHYSIOGRAPHY OF THE REGION. 13

streams, having cut through the Neocene cover of andesitic breccia, 

are still energetically sinking their steep-walled, V-shaped canyons into 

the underlying granitic rocks. These canyons as yet show little tendency to widen out into valleys, and remnants of the former extensive 

covering of andesite are often preserved on their very brinks. The 

vigorous nature of this trenching is well shown in the deep canyon of 

the Mokelmnne River, of which a small portion comes within the map 

just north of Bear Yalley, and also^in the whole canyon of the Middle 

Stanislaus. There are probably few better illustrations of a young 

V-shaped canyon than can be seen by looking westward from a point 

about halfway down the trail-which is shown descending into the gorge 

a mile and a half west of Mount Knight.

From Clover Meadow eastward the character of the country changes, 

although the change is not an abrupt one. The various residual 

andesitic ridges which have converged just west of Clover Meadow 

extend eastward as a single main ridge into the area of the Dardanelles quadrangle, between Highland Creek on the north and the Middle 

Stanislaus River on the south. About 2 miles east of Clover MeadQw 

the ridge ends in a steep bluff about 400 feet in height. The brink of 

this declivity affords a view (PI. Ill) which, aside from its somewhat stern beauty, is of considerable interest. For many miles to the 

northeast the eye overlooks a wild, hummocky surface of bare and glaciated granite, 1 stretching up toward the crest of the range, its dazzling 

whiteness being only partly relieved by a sparse growth of pines. In 

the near foreground the bald hummocks are interspersed with small, 

bright-green meadows, fringed with quivering aspens, and usually inclosing a.lakelet. Immediately to the east, and just across the low, 

hummocky foreground, the dark and rugged peaks of the [Dardanelles 

rise to an altitude 9,529 feet above the sea. The nearest peak, which 

may be conveniently called the West Dardanelle, can be plainly seen to 

be made up of a series of nearly horizontal volcanic layers, resting upon 

the granite and capped by a heavy flow of dark columnar lava, forming 

vertical cliffs several hundred feet in height. Beyond the Dardanelles 

appear the higher peaks forming the crest of the Sierra, also in part 

capped by volcanic rocks in nearly horizontal attitudes. These embrace some well-stratified andesitic tuffs, as observed by Turner 2 on the 

summit of Aruot Peak at an elevation of.10,000 feet.

This higher portion of the Sierra slope can not, then, like that west 

of Clover Meadow, be characterized as a series of more or less linear 

lava-capped ridges, separated by narrow canyons. The possibility of 

riding easily along the flat ridge tops has ended with the bluff upon 

which the observer stands. From here on to the summit the Neocene 

volcanic covering has been so thoroughly dissected and carried away 

that only a few scattered remnants testify to its once great extent.

'The term granite is used throughout this paper in a general sense, including all the "granodiorite," quartz-mica-diorite, etc., as well as true granite. 

2Geology of the Sierra Nevada: Seventeenth Ann. Kept. TJ. S. Geol. Survey, Part 1,1896, p. 708.
14 LAVA FLOWS OF THE SIERRA NEVADA. [BULL.89.

The region is best described as a rolling and huinmocky granitic slope 

a portion of the old peneplain modified by ice action and by recent 

erosion. Above this old surface stand isolated peaks and clusters of 

peaks, often true flat-topped buttes, composed of volcanic materials. 

Distinctly below it are the deep trenches of the larger streams, their 

character being well shown in the fine gorge of the Middle Stanislaus, 4 

miles southeast of Clover Meadow. An idea of the general character 

of the region may be gained from PI. X (p. 32), which is a view of the 

Dardanelles from the south, looking across the canyon of the Stanislaus. 

The foregoing account of the physiography of the region embraced 

in the accompanying map (PI. II) is little more than a bare outline, 

intended to present some picture of the old uneven peneplain, with its 

Neocene cover of fraginental audesite, down which the latitic lavas 

flowed, and of the general character of the erosion by which it has 

since been modified. No reference has been made to the influence of 

ice action upon the drainage, for the reason that there is no patent 

evidence that the important streams have retained any traces of ice 

interference. Definite moraines are rare, and although a few morainal 

patches occur on some of the ridges as low down as 5,500 feet, they are 

not shown on the present map. Various details of topography which 

are closely connected with the occurrence and distribution of the latites 

can be more intelligibly discussed under that head than in a general 

preliminary sketch, and will be for the present deferred.

THE OCCURRENCE AND DISTRIBUTION OF THE LAVAS

(LATITES).

The latites were early differentiated in the field into three varieties, 

belonging to at least three distinct flows. These are, in the order of 

their geological sequence: (1) a dark, compact augite-latite of <sowewhat basaltic aspect, with conspicuous tabular crystals of labraclorite 

and smaller phenocrysts of augite, which for convenience will be 

referred to as the Table Mountain facies; (2) a moderately dark-gray 

biotite-augite-latite, in which glistening tablets of biotite are the most 

conspicuous phenocrysts; (3) a dark, very compact augite-latite, with 

small, scattered phenocrysts of labradorite and augite, which may be 

called the Dardanelle facies from its occurrence on the extreme summit 

of the West Dardanelle.

The Table Mountain facies forms the longest flow of the series, having been traced from the West Dardanelle, where its surface attains an 

elevation of about 8,600 feet, down to Knights Ferry, where it forms 

plateaus, with black, bowlder-strewn surfaces, about 500 feet above 

sea. The rough, bowlder-like masses, from a foot to 2 feet in diameter, 

locally known as "nigger-heads," which are frequently abundant on 

the surface of the flow near Knights Ferry, are of the same character 

as the solid lava beneath them; and as the latites rarely show any
BULLETIN NO. 89 PL. II)

E HUMMOCKY GRANITIC SURFACE IN THE FOREGROUND AND THE CREST OF THE SIERRA NEVADA

IN THE DISTANCE.
KANSOME.] OCCURRENCE OF THE LATITES. 15

signs of weathering into soil, these were possibly originally loose 

fragments borne along on the surface of the lava stream.

My information concerning this portion of the Table Mountain flow 

is incomplete. It is known to extend almost continuously for 7 miles 

up both banks of the river, to Byrnes Ferry, forming irregular, plateaulike areas which break off abruptly on the river side in vertical columnar cliffs. These areas were evidently continuous at one time, but have 

been dissected by the river, now flowing several hundred feet below 

them. Andesitic breccia is reported by Turner 1 beneath the Table 

Mountain flow at Byrnes Ferry, and a considerable bed of similar breccia occupies the same relative position just south of McCartney Creek, 

about 4 miles northeast of Knight's Ferry.

Near Byrnes Ferry the flow turns eastward, leaving the'river and 

entering the edge of the Sonora quadrangle just west of Montezuma, or 

about latitude 37° 53'. Here it again resumes a northeasterly course, 

running generally parallel with the Stanislaus Eiver at an average distance of about 5 miles to the southeast, until it enters the southern 

border of the Big Trees quadrangle, just west of Shaws Flat. It is 

this section of the flow that is known as the Tuolurnne Table Mountain, 

a physiographical feature of considerable natural and historical interest. The old river gravels in the Neocene channel, beneath the so-called 

basalt, being auriferous, were actively exploited during the earlier days 

of mining activity. The line of famous Mother-Lode veins, passing 

through Angels, Carson Hill, Eawhide, and Quartz Mountain, runs 

beneath the lava near Eawhido, and reappears on the southern side as 

a heavy vein, determining a small southeast spur shown on the map. 

Being thus in the center of one of the most productive mining districts 

in the State, several references to the Tuolurnne Table Mountain are 

found in the older geological literature of California. Trask,2 writing 

in 1856, says:

This celebrated locality, of which so much has been said and written of late, is one 

of the most remarkable and interesting places to be found in this State.

That portion of the mountain which has so recently attracted attention on account 

of the placer deposits found beneath its surface is situated near the towns of Sonora 

and Columbia, being about equidistant from either locality. A portion of Shaw's 

Flat is situated immediately at its base. The superior portion of the mountain is 

composed of basaltic rock having the prismatic form; but in a few instances, at different points, it assumes the pentagonal shape so common to the columnar form of 

this rock.

I have traced this basaltic overflow in an east and west direction for the distance 

of nearly 40 miles on its course, and it is probable that it will be found to extend to 

a much greater distance eastwa.rd than at present known.

Its breadth is very variable throughout its course, in no instance, I believe, less 

than 400 feet, and often one-fourth of a mile. It seems to have followed the course

1 The rocks of the Sierra Nevada: Fourteenth Ann. llept. TJ. S. GeoL.Survey, Part , 1894, p. 491.

2 Report on the Geology of Northern and Southern California, Sacramento, 1856; State Senate Doc. 

14, p. 20.
16 LAVA FLOWS OF THE SIERRA NEVADA. {BULL. 89.

of a stream, filling its bed and banks, and to have flowed in this course for the 

entire length that it is now observable upon the surface.

To the east [sic] of Columbia it crosses the present bed of the Stanislaus at two 

different places, but what its position beyond this may be is at present unknown 

with any degree of certainty. From the relative position of the Stanislaus at the 

present time, the evidences are almost demonstrative that at the period of its occurrence it flowed into and down the former bed of this river, displacing the latter and 

filling up the space between its banks. The depth of the banks to the bed may be 

puetty accurately measured by the thickness of the basalt above that bed, which is 

about 100 feet on a general average.

Professor Whitney, in his volume on the geology of California, 

devotes several pages to a description of this portion of the flow, and 

of the auriferous gravels beneath the lava, accompanying his report 

with illustrations and sections. His account is too long to quote entire, 

but the following portions are pertinent to the lava flow itself, and are 

characterized by Whitney's usual graphic descriptive power:

One of the most striking features in the topography and geology of Tuolumne 

County is the so-called "Table Mountain," a name given throughout the State to 

the flat table-like masses of basaltic lava which have been rendered so conspicuous 

by the erosion of the softer strata on each side, and which now exist as elevated 

ridges, dominating over the surrounding country and remarkable for their picturesque beauty, but still more so on account of the important deposits of auriferous 

detritus which lie beneath them.

The Table Mountain of Tuolumne County is a flow of lava originating in the lofty 

volcanic region beyond the Big Trees of Calaveras. .... It comes down on the north 

side of the Stanislaus, forming a nearly continuous ridge, elevated more than 2,000 

feet above the river. Just below Abbeys Ferry ("Abbott Ferry " on map) the Stanislaus has broken through the once continuous basaltic ridge, which has been irregularly worn away for some distance from the river, but which reappears as a 

continuous mountain a little southwest of Columbia and continues on the south side 

of the river, forming a conspicuous feature of the scenery as far as Knights Ferry, 

a distance of about 20 miles from the point where it crosses the river and enters 

Tuolumne County. As seen from a distance, this Table Mountain reveals its origin 

at once in the contrast between the long straight line of its upper edge and the 

broken and curving ones which eroded hills of. the auriferous slates everywhere 

exhibit. Its dark color and the comparative absence of trees or shrubs on its top 

and sides also indicate very clearly that the material of which it is composed is very 

different from that of the surrounding hills.

On approaching Table Mountain and examining the material of which it is composed, and the position which it occupies, it is seen at once that it is a vast lava flow, of 

which the upper surface remains very nearly at the level and with the form which it 

originally had at the time of its consolidation, while the edges and the surrounding 

country have been denuded and washed away, so that the topography of the region 

is entirely different from what it was; in fact it is almost the reverse of it. No one 

can deny that a stream of melted lava, running for 40 miles down the slope of the 

Sierra, must have sought and found a depression or valley in which to flow, for it is 

impossible that it should have maintained, for any distance, a position on the crest 

of a ridge. Nor could the valley of the Stanislaus, now 2,000 feet deep, have existed 

at that time, for this flow of lava is clearly seen to have crossed it at Abbeys Ferry. 

The whole face of the country must, therefore, have undergone an entire change since 

the eruption took place during which this'inass of lava was poured out. ....

The summit of Table Mountain is occupied by a heavy bed of basaltic lava, of a 

very dark color and dense texture. It is occasionally distinctly columnar, and
HANSOMB.] OCCURRENCE OF THE LATITES. 17

appears to luivo all been poured out in ono flow, as there are no partings or divisions perceptible in the mass, which in the vicinity of Sonora is from 140 to 150 feet 

in thickness. Its width, at a point near the Buckeye Tunnel, was found to be about 

1,700 feet. The sitrface of the basalt is very nearly level, with a gentle slope down 

the valley. 1

In his volume on the auriferous gravels,2 the same writer summarizes 

his earlier account of the mountain, adds some further notes, and 

appends an outline map showing the approximate extent of the dissected lava flow between Abbeys Ferry and Knights Ferry. He also 

gives several transverse sections showing the structure of the mountain as revealed by mining operations. He speaks of the "basalt" 

overlying the andesite breccia, a relation which both Mr. Turner and I 

have confirmed at several points.

To the descriptions quoted there is little to be added concerning this 

portion of the flow, save to note that it attains a width of three-fourths 

of a mile northwest of Moutezuma, and that the columnar structure is 

a decidedly noticeable feature of the dark crags which surround the 

mountain in this region, rendering it an almost impassable barrier, and 

its level top a secure resort for hawks and eagles. Eoads skirt the 

cliffs on either side, but a practicable route across the line of the flow 

is found only where the volcanic cap has been cut through by erosion, 

effected by an undermining of the softer underlying rocks. The main 

stage road, connecting Sonora with the Great Valley, passes through 

such a gap about three-fourths of a mile northwest of Shaws Flat.

The extent of the general erosion that has transformed the old 

Neocene lava stream into the most imposing and continuous mountain 

mass in the vicinity is Avell shown in one of Whitney's wood cuts,3 

which pictures the Table Mountain from the southeast, probably near 

Chinese Camp, with the Bear Mountains (monadnocks) rising in the 

distance above its' even crest line,,

North of Shaws Flat, the Table Mountain flow turns westward 

toward the Stanislaus Eiver. Just west of Springfield it appears to 

rest in a shallow trough eroded in audesitic breccia, but this relation 

could not be definitely established. It terminates a mile to the south 

of Parrott Ferry in a columnar cliff overlooking the canyon of the 

Stanislaus, the stream flowing a thousand feet below the bottom of 

the lava. Looking northward, across the river, the continuation of the 

flow can be seen as a dark capping upon the summit of a granite peak 

rising precipitously from the water's edge, just west of the ferry. The 

base of the latite is here 1,100 feet above the' bottom of the canyon 

and rests directly upon the granite. The distance between the two 

dissevered portions of the flow is just under 1£ miles.

From Parrott Ferry northward the flow has been, dissected into a 

chain of separate but closely contiguous areas, which extends for 8

'Geological Survey of California, Vol. I, Geology, 3805, pp. 243-246.

2 Auriferous Gravels of the Sierra Nevada: Mom. Mus. Couip. Zool. Harvard Coll., Vol. VI, 1880, pp. 

131-137. 

3 Geology of California, 1865, p. 244, iig. 30.

Bull. 89 2
18 LAVA FLOWS OP THE SIERRA NEVADA. [BULL. 89.

miles along the west bank of the Stanislaus, regularly gaining in elevation, until the base of the flow at the end of this distance has an 

altitude of 3,000 feet above the sea and about 1,800 feet above the bed 

of the Stanislaus, giving a grade of about 125 feet to the mile.

Along this 8 miles the Table Mountain latite reposes upon a variety 

of underlying rocks. At the southern end, near Parrott Ferry, it 

rests upon granite. About three-quarters of a mile farther north the 

underlying rock is a limestone, belonging to the Calaveras formation.1 

The chief evidence for regarding this limestone as of Carboniferous age 

is the occurrence of Fusulina at Hites Cove.2 A portion of the lava 

also rests upon the nearly vertical edges of a lenticular area of 

quartzose Calaveras schists inclosed in the limestone. Between the 

latite and the schists is a thin layer of breccia made up of fragments of the underlying schist. Still farther north the third area 

shown on the map is separated from the limestone by a thick deposit 

of auriferous gravel. Due east of the town of Yallecito the latite rests 

upon a bed of white rhyolitic tuff 200 feet in thickness, which in turn 

rests upon gravels. The rhyolite, although very plainly a tuff, is frequently divided into small columns by a rather regular prismatic parting. In one case where these columns were measured they were found 

to average 4 or 5 inches in diameter and about a foot in length between 

the joints. Columnar structure in tuffs, while not common, is not 

unknown. Moderni, as cited by Washington, 3 describes a columnar 

trachytic tuff in the Bolsena region.

To the east and southeast of Douglas Flat the relation of the latite 

flow to the ordinary aiidesitic breccia of the region and to the rhyolitic 

tuff is very interesting. The main ridge which separates Douglas Flat 

from the canyon of the Stanislaus is made up chiefly of andesitic breccia in a succession of nearly horizontal beds of great aggregate thickness, in places at least 700 feet, resting sometimes on the Bed-rock 

series and sometimes on an underlying bed of rhyolitic tuff. The latite 

flow occurs, not as a rule on the crest of this breccia ridge, but on its 

eastern side, overlooking the deep canyon of the Stanislaus, in characteristic flat-topped benches. These thin out on the west and overlap 

unconformably upon the andesitic breccia, while on the east they are 

terminated abruptly by perpendicular cliffs, frequently over 200 feet 

high, from whose edges are obtained grand views into-the canyon 

below. At the base of these cliffs there is a bed of white columnar 

rhyolitic tuff, which appears to be at least 100 feet in thickness, and 

beneath this again a bed of auriferous gravel, varying in thickness and 

sometimes locally lacking. By a rather curious coincidence these 

benches of latite hang upon the slope at just the proper altitude to conceal the base of the andesitic breccia upon which they partly rest, the 

latter not appearing at the bottom of the cliffs at any point visited.

~ ' See Gold Belt folios; also Lindgren, Am. Jour. Sci., 4th series, Vol. Ill, 1897, p. 302.

2 Turner, Fourteenth Ann. Kept. TJ. S. Geol. Survey, Part II, 1894, p. 44G; also Seventeenth Ann. 

Kept., Part 1,189G, p. 600. 

3 Italian petrological sketches: Jour. Geol., Vol. IV, 1896, p. 543,
UANSOME.] OCCURRENCE OF THE LATITES. 19

From the northern end of this.' chaiii of dissected areas there is a 

gap of 3 miles before another remnant of latite is met with, capping a 

small hill just south of Mill .Creek. The structure of this hill is rather 

complicated. On its western side the massive augite-latite is separated from the Bed-rock series by three beds of soft, light-colored tuff, 

while on the eastern side the place of the tuffs is taken by a sheet of 

gray, highly glassy lava with a pitchstone-like luster, which has been 

found to be a vitrophyric biotite-latite, somewhat resembling petrographically certain faci'es of the biotite-augite-latite forming the second 

flow of the series, and which is generally found resting upon the Table 

Mountain flow when the two lavas occur together. Chemical evidence 

seems to indicate, however, that it is perhaps a remnant of a distinct 

and earlier flow which preceded the Table Mountain flow.

Between the vitrophyric lava and the augite-latite cap occurs a very 

thin layer of reddish lava, of somewhat uncertain affinities, which has 

been found at only one other point, near Clover Meadow, and is there 

apparently beneath the Table Mountain flow. There is thus an indication that the long Table Mountain flow was not really the first of the 

latitic eruptions, but may have been preceded by a vitrophyric lava 

very similar to the biotite-augite-latite which preceded the Dardanelle 

flow. The field studied, however, affords no certain evidence on this 

point, and it must be left as a possible contingency that may meet 

with confirmation or denial when the geology of the Dardanelles quadrangle is fully investigated.

Immediately to the north of Mill Creek there is a small mass of the 

vitrophyric lava hanging upon the slope of a small spur overlooking 

the Stanislaus. It is evidently a continuation of ttie fragment south 

of Mill Creek, but here occurs alone, resting upon the edges of the 

Calaveras quartzite.

Following up the western bank of the North Fork of the Stanislaus, 

a small remnant of the Table Mountain flow is found about a mile and 

a half east of Manuel's, perched on the brink of the canyon at an 

elevation of about 3,200 feet and resting immediately on the granite.

A quarter of a mile farther upstream an interesting portion of the 

flow is encountered, which extends along the river almost continuously 

for 3£ miles to Squaw Hollow. The comparatively shallow drainage 

area of Love Creek is separated along this distance from the deeper 

canyon of the North Stanislaus by an even, flat-topped ridge, capped 

for the greater part of its length by andesitic tuff and breccia. The 

Table Mountain flow not only occupies the greater part of the valley of 

Love Creek, but also forms a distinct bench on the river side of the 

ridge, just below its crest. The outer edge of this bench is nearly 

always a vertical cliff, and the latite can generally be seen resting upon 

the granite. The relation to the andesitic breccia at the rear of the 

terrace is not easily determined. It is not always plain whether the 

andesite breccia is the later and rests upon the latite, as the mapping 

at first sight suggests, or whether the latter is really the younger rock,
20 LAVA FLOWS OF THE SIERRA NEVADA. [BULL. 89.

which, having flowed down a channel cut through the breccia, has by 

a curious coincidence left its remnants lying unconformably upon both 

granite and breccia in such a way as to conceal their contact. In spite 

of its inherent improbability, there are indications which point to the 

latter hypothesis as the true one, especially as a similar relationship 

was observed east of Douglas Flat. That such a condition does obtain 

only a short distance away is shown at a point 1£ miles south of Squaw 

Hollow. (PL IY.) Here the nearly horizontal beds of light-gray 

andesitic breccia, with an aggregate thickness of 700 feet, are well 

exposed in a steep, bare slope, the lowermost bed reposing on the 

granite. The base of the Table Mountain flow is also very well 

exposed, and can be seen resting in striking iiucomformity upon the 

eroded edges of the horizontal breccia beds, the plane of contact sloping down toward the river at an angle of about 20 or 25 degrees. The 

bottom of the flow is separated from the breccia by a thin layer of 

andesitic rubble or conglomerate, evidently derived from the underlying beds. -Above this somewhat angular conglomerate comes the 

vesicular and more or less brecciated under surface of the massive 

latitic flow, passing, a little higher up, into a horizontally platy structure, which in turn is succeeded by a rude columnar parting. Although 

the base of the flow slopes down toward the bottom of the canyon at a 

considerable angle, its upper surface is more nearly level and forms 

a gently sloping bench, which breaks off abruptly toward the river in 

cliffs from 100 to 150 feet in height.

There is thus proof at this point, not only that the Table Mountain 

flow rests unconform ably above a considerable thickness of the audesitic breccias, but that, at the time of its extrusion, the latter beds had 

been extensively eroded and a channel cut in them, which, here at 

least, was closely coincident with, though not so deep as, the present 

canyon of the North Stanislaus.

Near the crest of the ridge the Table Mountain flow becomes quite 

thin, and is overlain by biotite-augite-latite about 100 feet in thickness, 

which in turn is capped by about 75 feet of augite-latite, here occupying the summit of the ridge. This upper flow is lithologically nearly 

identical with the Table Mountain flow, but has somewhat smaller 

plagioclase phenocrysts, and on account of its position is correlated 

with the Dardanelle flow. The biotite-augite-latite occurs in three other 

places on the river slope of the ridge, in every case in small patches 

resting upon thicker masses of the Table Mountain flow. It is best 

seen, however, to the west of the ridge, in the little valley of Love 

Creek.

A few yards east of McKay's mill the attention is arrested by a low, 

gently arching lobe of dark-gray lava, which rises from the narrow 

floor of the valley with so clean and bare a surface that it appears to 

have been erupted within historical times. Its surface shows no sign of 

weathering, and is divided by cracks into rough polygonal blocks from
.ULLETIN NO. 89 PL. IV

FORMABLY UPON BEDS OF FRAGMENTAL ANDESITE SOUTH OF SQUAW HOLLOW.

d is andesitic breccia in nearly horizontal beds, upon whose edges the rudely columnar augite-latite can be seen resting

n the upper left-hand portion of the illustration,
RANSOME.] OCCURRENCE OP THE LATITES. 21

a foot to 2 feet in diameter. The rock cleaves most readily transverse to these rude vertical columns, the cleavage faces showing the 

characteristically abundant, glistening biotite crystals of the biotiteaugite-latifee. Upstream from McKay's mill the latite is found to fill 

most of the bottom of the little canyon, with a final isolated patch 

resting in the col at its head. As the ravine itself is excavated in 

granite, it is evident that it must have existed in substantially its 

present shape before the lava flow took possession of its stream bed. 

In other words, it is a remnant of a small Neocene valley. This result 

is startling when it is remembered that the main Stanislaus Eiver has 

cut a gorge 1,000 feet deep directly across the Table Mountain flow 

upon Avhich a portion of this .biotite-augite-latite rests, while near 

Sonora the waste of the surrounding country has been sufficient to leave 

the same flow as a mountain mass, conspicuous for miles around. But, 

startling as it appears, there seems to be no avoidance of the conclusion 

here drawn. This survival explains why the old peneplain character is 

better preserved in this portion of the Sierra slope than in the foothill 

region; the rocks are more homogeneous and resistant, and the active 

erosion is largely concentrated in the deep canyon-cutting of the 

longer and more vigorous streams. This phase of denudation, although 

productive of striking results, is least calculated to obscure the peneplain character of the surface upon which it acts. It is quite probable 

that the present small stream of Love Creek has had its cutting power 

greatly decreased by the capture of its former head-water drainage by 

the deepening and widening of the North Stanislaus Canyon.

Near Squaw Hollow the line of the flow turns eastward and crosses 

the present canyon of the North Fork of the Stanislaus, another obvious 

instance of deep cutting since the eruption of the lavas. This canyon 

is not to be compared to that of the Middle Stanislaus, but some idea 

of its depth and the steepness of its walls may be gained when it is 

stated that the trail connecting the two groves of mammoth trees 

crosses at this point on a narrow bridge, and a horseman must travel 

more than 12 miles in a straight line up or down the stream before 

corning to another practicable crossing.

Two miles east of Squaw Hollow a remnant of the Table Mountain 

flow occurs resting upon a ridge of granite and surmounted by a small 

patch of the biotite-augite-latite. Another fragment occurs on the 

same ridge a little farther'east. From these small areas there is a 

considerable gap in the continuity of the lava flows, until they are met 

with again, some 3 miles to the east, in the upper drainage of Griswold Creek. The most interesting occurrence here is about 1£ miles 

south of Fenuessy Meadow, on the divide between Griswold and Skull 

creeks, where a portion of the biotite-augite-latite can be plainly seen 

resting upon the audesite breccia, and in turn covered by a second bed 

of the latter. The volcanic rocks at this point cap a small elliptical 

hill and rest upon the basal granite of the region. At the eastern end
22 LAVA FLOWS OF THE SIERRA NEVADA. [BULL.89.

of the hill the latite is about 40 feet thick, and well exposed on the 

southern side, resting upon the breccia. Above the latite is a bed of 

soft, light-colored tuff, about 15 feet thick, which in turn is overlain by 

the ordinary andesitic breccia which caps the hill. At the west end of 

the hill a similar sequence is exposed, only here the latite is not more 

than about 25 feet thick, and rests directly upon the granite. Just to 

the east of the hill is a strip of augite-latite which appears to underlie 

the biotite-augite-latite, but the relation is not clearly shown. Other 

considerable masses of. augite latite occur on GriswOld Creek, above 

Fennessy Meadow, but they were somewhat hastily examined, and it 

is not known whether they should be correlated with the Table Mountain flow or with the Dardauelle flow. . Near the head waters of Beaver Creek the audesitic breccia surrounds 

an area of granite, portions of which are higher than the bottom of the 

breccia, indicating a considerable irregularity in the old peneplain at 

this placet The biotite-augite-latite occurs at three points about the 

edge of this inclosed area, resting on the granite at the base of the 

breccia, and apparently overlain by the latter. The southernmost of 

the three patches is overlain by a portion of the Dardanelle flow.

The line of the latitic flows crosses the main breccia ridge at this 

point and appears on its eastern side in the drainage area of the Middle 

Stanislaus. Whether the flows are really continuous under a portion 

 of the andesitic breccias is a.question that was not determined with 

absolute certainty. The mapping indicates such a continuance, and 

the hypothesis is strengthened by the fact that on the eastern side of 

the ridge a portion of the sloping terrace formed by the Dardanelle 

flow and the underlying biotite-augite-latite is occupied by a small 

meadow, with strong springs issuing from beneath the andesitic breccia 

at its rear. As such springs are not common along the sides of these 

ridges, save where the porous breccia beds rest upon an impervious 

foundation, the presumption is that the massive Dardauelle flow here 

passes beneath a portion of the clastic series.

To the south and east of Clover Meadow the latites are well exposed. 

They occupy in general the crest of the ridge already described as 

running eastward toward the Dardanelles, and rest with evident unconformity upon the andesitic breccias and tuffs, or directly upon the 

granite, as seen about a mile to the south of Clover Meadow. All 

three of the flows are represented on the ridge. The earliest or Table 

Mountain flow is the most extensive, and rests upon a rather uneven 

surface of the clastic audesites. It varies greatly in thickness from 

point to point, and has a warped and twisted surface, rendering its 

mapping difficult on a small scale. At the western end of the ridge, 

about half a mile due east of the small pond in Clover Meadow, 

occurs an insignificant patch of the red lava, identical with that 

found south of Mill Creek, and occupying a position below and 

apparently geologically beneath the Table Mountain flow. Near the
\D. 89 PL. V

E MOUNTAIN FLOW AND THL UNDERLYING ANDESITIC BRECCIA 1.1 MILES EAST OF CLOVER MEADOW.
OCCURRENCE OP THE LATITES. 23

eastern end of the ridge the contact of the latite with the clastic 

andesite is finely shown (PI. V). The lower portion of the massive 

flow is usually highly vesicular, and at the point shown in the illustration there is a cavity about 3 feet in height in the under side of the 

flow, its interior being lined "with exceedingly frothy lava. At a short 

distance from the bottom the latite becomes less vesicular and takes 

on the usual platy structure, passing with increasing thickness into 

columnar parting. The character of the underlying andesite at this 

place is shown in PI. VI. The material shows a rude stratification 

and the fragments are rounded or subaugular, indicating that they 

were water deposited.

As already noted, the eastern end of the ridge falls off abruptly in a 

high blufl?, in which are exposed over 400 feet of nearly horizontal beds, 

composed of andesitic sands and gravels partly consolidated. They 

form a part of the audesitic tuff series, but are somewhat more Avaterworn and better stratified than usual in this region. (PI. VII.) The 

craggy masses in the upper right-hand corner of the illustration are 

composed of an andesitic breccia, which lies at a considerable angle 

and unconformably upon the stratified audesitic beds and underlies the 

Table Mountain flow. It appears to belong to the period of latitic 

eruptions, and to have immediately preceded the first of these. It 

has very little horizontal persistence, but is probably the equivalent of 

the conglomerate noted in a similar position beneath the lower latite 

flow, east of McKay's mill.

At the western end of a little nieadow lying on the crest of the ridge, 

near its eastern end, the Table Mountain flow exhibits the interesting 

rounded forms shown in PI. VIII. These recall certain spheroidal 

structures occurring in the Mesozoic basalts at Point Bonita, 1 in the 

Coast Eanges, although they are not so perfect as the latter. They 

are clearly not due to weathering and exfoliation, as the surface 

shown is perfectly bare of soil and exhibits only the merest traces of 

superficial decomposition. It is undoubtedly a structure produced 

during the cooling of the molten mass, and is replaced a few yards away 

by the ordinary columnar structure (PI. IX). The surface shown in the 

illustration, PI. VIII, is probably but little different from that of the 

original flow, and exhibits well its locally rolling character. That the 

ice at one time surmounted the ridge is indicated by the granitic bowlders which occur perched here and there upon the lavas, but it does 

not appear to have acted as an effective eroding agent.

At various places on the ridge the biotite-augite-latite rest's upon the 

Table Mountain flow with an average thickness of something less than 

50 feet, while on top of it again are masses of the Dardanelle flow, with 

an observed thickness of 100 feet. This latter rock generally shows a 

smaller columnar structure than the Table Mountain flow, the columns 

being rarely a foot in diameter and usually short and irregular.

>Univ. of Calif., Dept. Geol., Bull., Vol. I., 1893-90, pp. 71-114.
24 LAVA FLOWS OF THE SIEERA NEVADA. [BULL. 80.

'Probably no known area in the Sierra Nevada presents a more interesting succession of volcanic rocks than the cluster of peaks known 

as the Dardanelles. As a whole they have never been closely studied, 

and the present information has been derived merely from a short 

reconnaissance of the western peak, and- an ascent to its summit. 

This peak is made up of a series of volcanic flows resting upon the 

granite as a basement, at an elevation of about 7,500 feet above sea. 

On the west side (the side shown in PI. Ill) the lower member of the 

volcanic series is composed of several flows of olivine-basalt, aggregating from 500 to GOO feet in thickness. This basalt has suffered 

greater decomposition than the latites, and forms a steep, weathered 

slope, leading up to the base of the lofty cliffs which give the peak its 

striking outline. That the rocks composing this slope are true surface 

flows is indicated by the frequent vesicular and amygdaloidal bands 

from 10 to 40 feet in thickness, which are exposed in the small gullies 

channeling the weathered rock. The vesicles are usually lined with 

zeolites in the form of thin incrustations.

Besting sometimes directly upon the olivine-basalt, sometimes sepparated from it merely by a thin layer of volcanic conglomerate, is a 

thick mass of dark, columnar augite-latite, forming a vertical cliff 

over 400 feet in height.. The lower 25 or 30 feet of the cliff face shows 

a very vesicular facies, becoming compact and columnar higher up. A 

short distance away from the mountain it could be seen that the columns became much larger some distance up the cliff, but it was not 

possible to determine whether this difference in size was significant of 

any division into an upper and lower flow, or whether the whole cliff 

face consisted of the Table Mountain flow. Hand specimens from the 

base of the cliff show a facies much like the typical Dardanelle flow, 

while fragments fallen from the upper portions exhibit the thoroughly 

characteristic features of the Table Mountain facies. The difference, 

however, is not greater than might easily obtain between the middle 

and basal portions of a single thick flow.

The conglomerate, mentioned as occurring between the olivine-basalt 

and the base of the latite, is composed chiefly of waterworn volcanic 

pebbles, some of which are identical with the underlying basalt, while 

others appear to be andesitic, or possibly latitic, in character. The 

bed is a lenticular one, about 12 feet in thickness and of small lateral 

extent.

Bhyolitic material was not observed on the west side of the peak, but 

an area of massive rhyolite is shown on the map just west of the peak 

arid crossed by the trail going down to Highland Creek. This is the only 

-area of undoubtedly massive rhyolite met with in the district embraced 

by the map. It rests immediately upon the granite, and. like the rhyo 

litic tuff of the region, is probably older than the andesites and latites.

Above the heavy columnar Table Mountain flow, and forming the 

extreme summits of the West Dardauelle, some rounded, dumpling-
 UNDERLYING TABLE MOUNTAIN FLOW H MILES EAST OF CLOVER MEADOW.

ments and the rude stratification of the whole, These are outlying pinnacles left by differential erosion upon the steep nil I slope.
KANSOME.] OCCURRENCE OF THE LATITES. 25

shaped masses could be seen, which the glass showed to have the 

smaller columnar structure generally associated with the uppermost, 

or Dardanelle flow.

On the southeast side the ascent to the top of the peak is not difficult. It was found that the lowermost member of the volcanic series 

on this side is a rhyolitic tuff, inclosing foreign waterworn pebbles, and 

about 50 feet thick, probably resting on the granite, although, the base 

was not seen. Above the tuff the same olivine-basalt already mentioned is exposed for a thickness of 150 feet. The succeeding 300 feet 

of vertical elevation is occupied by a very rough talus slope, composed 

of fallen columns from the cliffs above, which on this side show a 

height of nearly 500 feet by aneroid barometer. The lower 200 feet of 

the cliff exposed is coarsely and somewhat irregularly columnar; 

toward the top this passes gradually into a zone characterized by a 

horizontally platy structure, which in turn is succeeded by an irregularly jointed and vesicular upper portion, becoming a flow breccia at 

the extreme top. No evidence was found on this side of the mountain 

to indicate that this thickness of 500 feet is made up of any more than 

the single Table Mountain flow. Its bottom, however, was not seen.

On the top of this thick flow, exposed in the saddles between the 

three summits shown on the map, lies the biotite-augite-latite of the 

second flow, here 50 feet in thickness.

The summits themselves are composed of remnants of the Dardanelle 

How, which on the western knob has a thickness of at least 100 feet. 

It shows the usual small columns and fresh bare surface, its dissection 

being due rather to an undermining and falling away of the columns 

than to its own weathering. The entire thickness of the latites here 

exposed is at least 710 feet, and of the entire volcanic accumulation 

above the granite 1,210 feet. These figures, however, are from aneroid 

readings, while the topographical map would indicate a total thickness 

of 1,400 feet. It is noteworthy that this thickness does not include 

any of the ordinary andesitic breccia which elsewhere occurs in such 

volume beneath the latites.

The Dardanelle Cone, 9,529 feet, the highest peak of the group, was 

not visited. .It owes its name to its sharp conical summit as seen from 

the west, but, like the West Dardanelle, appears to be made up of 

horizontal volcanic rocks resting upon the granite. The lower beds 

are light in color, suggesting rhyolitic or andesitic tuff's.

The view from the summit of the West Dardanelle is in many Avays 

an exceedingly interesting one. In the immediate foreground, to the 

west and north, lies a broad basin of bare, glaciated granite, rounded 

and polished by the ice, and dotted here and there with lakes or grassy 

meadows. To the south lies the gorge of the Middle Stanislaus too 

deep and narrow for its bottom to be seen, even from such a vanta,ge 

point. But if the eyes are withdrawn from what lies just below them 

and allowed to sweep the horizon, the attention is at once attracted by
26 LAVA FLOWS OF THE SIERRA NEVADA. [BULL.89\

the several peaks of similar structure to that upon which the observer 

stands; that is, they are made up of nearly horizontal flows or breccia 

beds, resting upon a granitic basement. Not only are they of similar 

structure, but they stand with their tops close to an imaginary plane 

having a noticeable slope to the southwest, the general western slope 

of the range, which is rendered more apparent when seen from so high 

an altitude. Toward the west the ridges are lower, and, as has been 

shown, are composed in part of the same latitic flows. To the east 

and northeast they are higher and less continuous, being frequently 

isolated peaks, and less is known of the nature of their volcanic caps. 

It is probable that they are in part composed of latite, as Whitney 1 

mentions the occurrence of lava similar to the Table Mountain flow 

south of Hermit Valley. But they are probably largely made up of 

the ordinary audesitic breccia of the range.2 This appears to be 

especially true of the ridges to the southeast across the main Stanislaus 

Eiver. It is evident that in Tertiary times this portion of the range 

was a peneplain, or a surface of comparatively gentle relief, which at 

the end of the Neocene was covered by volcanic tuffs and flows. 

Moreover, the latite now crowning the Dardanelles can not mark the 

upper limit of this accumulation, for, as has been shown in the preceding pages, these lavas flowed down channels in the andesite, and were 

in turn covered by fresh accumulations of the same breccia. The only 

remnants of all this volcanic covering now visible from the summit of 

the West Dardanelle are a few residual peaks and ridges which, owing 

to a more resistant capping, or to other causes, have survived the general 

degradation. The picture of profound denudation, shown in the 

uncovering of the old granite surface and its deep trenching by such 

streams as the Stanislaus, would be impressive in any case, but it 

becomes doubly so when it is remembered that all this has taken place 

in post-Tertiary times.

Thus far the latitic lavas have been described as if they were confined 

in their distribution to the main line of flow outlined in the preceding 

pages. But this is not entirely the case. As shown on the accompanying map, the biotite-augite-latite occurs in small isolated areas at considerable distances from the main flow-axis, even appearing in the 

drainage area of the Mokelumne Eiver, to the north of the Stanislaus 

Basin. It is possible that there may be a few more of these patches 

than have been indicated, as they frequently occur very unobtrusively 

near the contact of the andesite breccias with the underlying granite, 

and are often concealed in the heavy timber. In such situations it is 

generally impossible to determine positively whether the latite really 

underlies the audesite or vice versa. South of the Middle Stanislaus 

are several small areas of the biotite-augite-latite which plainly rest 

upon the audesitic breccias amd tuff's, in most cases with evident uncon1 Auriferous Gravels, 1880, p. 131.

2 See Turner, Geology of the Sierra Nevada: Seventeenth Ann. Kept. U. S. Gcol. Survey, Part 1,1890, 

pp. 708-709. for some interesting notes on this region, with views of the audesite breccia (PL XXXVI).
BULLETIN NO. 89

ABOUT 2 MILES EAST OF CLOVER MEADOW, SHOWING THE STRATIFICATION OF THE ANDESITIC BEDS. 

a resting unconforrrably upon the stratified tuffs and conglomerates and underlying the Table Mountain latite, which is not shown.
RANSOME.] MICROSCOPICAL PETROGRAPHY. 27

formity. This relation is well shown about 2 miles southeast of Mount 

Knight, where the latite, beginning with a point on the top of the 

ridge overlooking the Middle Stanislaus, runs obliquely down over the 

beveled edges of the nearly horizontal clastic andesite, resting finally 

on the schists of the Bed-rock series just above Kose Creek.

As will be seen in the section devoted to the petrography of the latites, 

the biotite-augite-latite has characteristics that render its distinction 

from a tuff not always easy. The fact that it has a wider distribution 

than the two undoubted massive flows, also suggests that it may have 

had a different origin. But the field evidence does not support the 

view that it is in any sense a water-deposited tuff. It is entirely 

devoid of the horizontal bedding characteristic of the known tuffs of 

the region, and on the other hand it possesses the more or less uneven 

upper and lower surfaces, and the ability to lie upon perceptible slopes, 

which are characteristic of true lava streams. It also resembles lavas 

in being coarsely columnar in structure, although, as has been shown, 

this structure may also occur in undoubted tuffs. The basal contact 

of the biotite:augite-latite was nowhere, seen sufficiently well exposed 

to give a decisive answer to the question whether it is tuffaceous or 

massive in character.

PETROGRAPHY OF THE LATITES AND OF THE OTHER 

VOLCANIC ROCKS ASSOCIATED WITH THEM.

As frequently emphasized in the preceding account of its distribution, the lava composing the Table Mountain and Dardanelle flows is 

dark in color and basaltic in general appearance. The earlier writers, 

without exception, referred to it as basalt, and until very recently no 

reason had appeared for revising their determination. In 1895, however, Turner wrote as follows:

The basalt of tkeTuolumne Table Mountain is also a dark, heavy rock, but as may 

be noted below [referring to an accompanying chemical analysis] has an unusually 

high percentage of silica for a basalt. It is also characterized macroscopically by 

containing numerous cavities and tabular porphyritic feldspars which are sometimes 

half an inch long. 1

In a later paper, published after the field seasons of 1895 and 1896, 

occurs the following paragraph:

Tertiary trachytes are known thus far only in the area of the Big Trees sheet. 

They occur both as tuffs (?) and massive flows,, the latter strongly resembling 

basalt in. macroscopic appearance. They are placed with the trachytes chiefly on 

the basis of their chemical composition. Indeed, the Tuolurnne Table Mountain 

basalt has so high an alkali content that it is placed in the table with the trachytes 

for comparison. This flow can be traced from Knights Ferry, in Stanislaus County, 

across the Sonora area into the Big Trees district, not fur from where specimens 

85 and 86 Tuolnmne were collected. As the writer has only cursorily examined 

these trachytes, the matter of their classification will not be further considered at 

present. 2

'Rocks of the Sierra Nevada: Fourteenth Ann. Kept. U. S. Geol. Survey, Part II, 1804, p. 491. 

2 Further contributions to tlie geology of tho Sierra Nevada: Seventeenth Ann. Kept. TJ. S. Geol. 

Survey, Part 1,1890, p. 729.
28 LAVA FLOWS OF THE SIERRA NEVADA. [nuLL.89v

By way of preliminary explanation, it may be stated that both the 

"trachytes" and the "basalt" referred to in the foregoing citation 

are portions of the latitic flows which form the subject of the present 

paper. This separation into trachyte and basalt, it will appear, was 

not without excuse so long as hand specimens from somewhat widely 

separated localities were made the basis for such distinction, and the 

mere fact that lavas belonging to one chemical and mineralogical type, 

if not, in some cases, to one flow, could be tentatively classed as 

trachytes in one place and basalts in another, is not without its bearing on the question of their proper classification.

THE TABLE MOUNTAIN FLOW.

Megascopically the Table Mountain latite shows great uniformity, 

from the end of the flow, near Knights Ferry, to the Dardanelles, the 

highest point at which it has been studied. It may become locally 

vesicular, especially at the top and bottom of the flow, or show slight 

variations in the number and sixe of the phenocrysts, but in general 

the description of any one hand specimen will apply with but slight 

modification to any portion of the 60 miles of flow.

A specimen (1820 S. N.) from just, west of Parrott Ferry, at the 

point where the river has cut its gorge across the line of the lava 

stream, may be considered as typical. This is a dark rock, of compact 

texture and basaltic aspect, characterized by an abundance of large 

glassy plagioclase phenocrysts lying in a dense, nearly black groundmass. The plagioclases are tabular parallel to the brachypinacoidal 

faces, a common size being about 2 Inm in thickness, 8 nnn in breadth, 

and 10 """ in length. A length of 15 mm may, however, be frequently 

observed. The cleavage faces, on the freshly fractured rock surfaces, 

always show twinning according to the albite law, and not infrequently 

an additional twinning following the Carlsbad law. Dark olive-green 

augite can be distinguished in the form of phenocrysts, but it is neither 

an abundant nor a conspicuous constituent as compared with the 

plagioclases. The rock is somewhat vesicular, the vesicles being 

usually elongated in the direction of flow, and occasionally filled with 

calcite.

Under the microscope the large plagioclase crystals are by far the 

most conspicuous mineral in the slide. Augite is much less abundant, 

but occurs in phenocrysts of considerable size and usually of irregular 

outlines. Olivine is moderately abundant in small, more or less idiomorphic phenocrysts up to 0.5 mm in length. The groundinass is 

hyalopilitic.

The large plagioclases generally show approximate crystallographic 

outlines, but they are often rounded and sometimes deeply embayed. 

Although perfectly fresh, they are apt to be crowded with inclusions of 

dark, glassy base, giving them a mottled appearance not unlike the
BULLETIN NO. 89 PL. VIII

L FACIES OF AUGITE-LATITE OF THE TABLE MOUNTAIN FLOW. 

of a little meadow on the crest of the ridge, about 1J miles east of Clover Meadow.
EANSOME.] TABLE MOUNTAIN FLOW. 29

crystal figured by Eoseubusch1 from a Hungarian augite-audesite. 

They are invariably twinned in accordance with the albite law, but 

the resulting lamellae are of very different widths, ranging from those 

just visible up to 0.5 """ or over. The frequent combination of Carlsbad with albite twins renders the determination of the feldspars by 

Michel Levy's method comparatively easy. In a section at right angles 

to the plane of the brachypinacoid, angles of extinction were obtained 

on each half of the Carlsbad twin of 14.5° and 33.5°, indicating a labradorite with about the composition Ab3 An4 . A section cut approximately parallel to thebrachypiuacoid and revealing no twinning showed 

the emergence of a slightly oblique acute bisectrix and gave an extinction angle of about 16° with the basal cleavage, the angle varying 

somewhat for different portions of the crystal.

Pericline lamella} are occasionally observed in conjunction with the 

albite twinning.

An attempt was made to determine the specific gravity of the plagioclase phenocrysts by suspending fragments in Thoulet solution. 

Some very small and apparently pure grains neither floated nor sank 

at 2.684, but the specific gravity of particles over a millimeter in diameter was found to be about 2.651. The latter figure is undoubtedly 

lower than the true specific gravity of the feldspar, as it is impossible 

to secure fragments that are free from inclusions and yet large enough 

to give satisfactory determinations by suspension in a heavy liquid.

The augite pheuocrysts are generally irregular and rounded in out 

line, but are sometimes crystallographically bounded in the prism zone. 

They are very pale green in color, nonpleochroic, and resemble diopsidej 

but the extinction angle on c is often over 40°, and sometimes as high 

as 45°, and they are more properly classed as pale augite. As Zirkel 2 

points out, such pale-green augites are characteristic of rocks high in 

alkalies, while brownish augites are more common in basalts.

The olivine, like the other minerals in the slide, is perfectly fresh, and 

forms small crystals, usually .less than 0.5 inm in length, and showing 

slightly rounded crystallographic outlines. Although occurring in 

much smaller crystals than the augite, it appears to be nearly as 

abundant in the thin section, and may be regarded as an essential 

constituent of the rock.

The groundrnass, from which the pheiiocrysts are distinctly differentiated, shows a rather coarse hyalopilitic structure, made up of feldspar 

microlites, grains of magnetite, augite, olivine, and glass. Structurally, 

it is very similar to the olivine weiselbergite of Eosenbusch,3 as seen 

in one of Voigt and Hochgesang's thin sections. The feldspar microlites usually show distinct albite lamella}, which extinguish at considerable angles, indicating a labradorite but little, if any, less basic than 

the phenocrysts. As one of the distinctive characters of the latites

1 Mikroskopischo Physiographic (3d ert.), Vol. 1,1892,1'l. XXIV, fig. 3.

2 Lehrbnch dor Potrographie, 2d ed., AT ol. I, 1893, p. 281.

3 Op. cit., Vol. II, 1896, p. 954.
30 LAVA FLOWS OF THE SIERRA NEVADA. [BULL. 89.

described in this paper is their relatively high potash content, and as 

Washington 1 has described orthoclase in rocks of almost identical 

chemical composition from Italy and Asia Minor, pains were taken to 

determine whether any of the microlites were potash feldspars. But 

microscopical study gives no ground for believing- that any other feldspar than labradorite is present. Some of the labradorite phenocrysts 

were observed to be bordered by an extremely narrow zone of more 

acid feldspar possibly orthoclase. This, however, is not common.

The glassy portion of the ground mass appears to make up less-than 

half its bulk. It is light brown in color, and quite turbid from the 

presence of very minute globulites. The magnetite occurs in small 

but distinct grains, rather abundantly and evenly distributed through 

the section. The olivine and augite grains in the grouudmass differ in 

no way but in their small size from the same minerals in the phenocrysts, and are not to be sharply differentiated from the latter. The 

olivine frequently occurs as inclusions in the augite, and the latter is 

sometimes included in the large labradorite phenocrysts. Apatite 

occurs in small prisms, commonly included in the augite.

Turner 2 has given a microscopical description of a specimen (36 S. N.) 

collected from Table Mountain near Shaws Flat. He says:

Microscopically the Table Mountain basalt shows large tabular feldspars, smaller 

augites, and numerous olivine grains in a nearly opaque groundmass, in which are 

very abundant feldspar microlites. This groundmass doubtless contains a large 

amount of magnetite, and strongly resembles some of the sections of the older 

basalt. There is a good deal of brownish serpentinoid substance in the groundmass. The porphyritic feldspars are polysynthetically twinned and have a corroded 

appearance, due to the abundant inclusions of aggregates of opaque particles, with 

some glass inclusions. There is also some serpentine in-the largo feldspars.

An analysis of this specimen is appended to his description and has 

been quoted in Column I of the table of chemical analyses on page 58.

Mr. Turner having kindly allowed me to examine two thin sections 

of this rock, it was found that it differed from most of the specimens 

collected at other points along the Table Mountain in the slightly 

greater abundance of the olivine, in the presence of the serpentinous 

patches, and in a rather unusual opacity in the glassy base. A single 

rounded crystal of slightly pleochroic orthorhombic pyroxene was noted 

included within a large augite phenocryst, but this mineral is very 

rare in the Table Mountain flow. The groundmass is hyalopilitic. The 

opacity of the groundmass is seen with high powers to be due to the 

dense crowding of minute globulites of rather peculiar character. 

These globulites occur also in the Dardanelle flow, and as they have 

been there more studied their description will be for the present 

deferred.

A specimen (1016 S. N.) taken on the trail passing over the top of

1 Italian petrological sketches: Jour. Geol.; Vol. IV, 1896, p. 547 et seq., ami On igneous rocks from 

Smyrna and Pergamon: Am. Jour. Sci., 4th series, Vol. Ill, 1897, pp. 41-50.

2 Bocks of the Sierra Nevada: Fourteenth Ann. Eept. U; S. Geol. Survey, Part II, 1894, p. 491.
IULLETIN NO. 89 PL, IX

ES OF THE AUGITE-LATITE OF THE TABLE MOUNTAIN FLOW.

e, The light-colored bowlders in the foreground and the larger masses on top of the lava columns are glacial erratics.
RAKSOME.] TABLE MOUNTAIN PLOW. 31

the mountain between Sonora and Tuttletown is thoroughly typical 

and shows particularly Avell the numerous inclusions in the large labradorite phenocrysts. These inclusions are usually composed of globulitic glass, with microlites of labradorite and augite, and are similar 

to the fine groundmass of the rock.

Northeast from Parrott Ferry the Table Mountain flow was investigated microscopically at many points, with the general'result of showing great structural and inineralogical uniformity. In general, as the 

flow is followed higher up into the mountains the olivine becomes 

somewhat less, abundant and sinks to crystals of smaller dimensions. 

The large labradorite phenocrysts, while preserving their size and 

characteristic mottling, seem, to become progressively slightly more 

acid, numerous determinations by the Michel L6vy method indicating 

that in the more eastern portions of the flow a labradorite of the 

approximate composition AbjAni predominates. Apatite is a constant 

accessory, occurring in the grouudmass and in tbe augites.

About 1^ miles southwest of Collyer's a facies (1845 S. IsT.) occurs in 

which the labradorite phenocrysts are somewhat smaller than usual, 

the rock standing megascopically about halfway between the normal 

Table Mountain facies and the usually finer-grained rocks of the third, 

or Dardanelle, flow. A thin section shows the usual phenocrysts of 

labradorite, augite, and olivine. The labradorites are twinned with 

beautiful sharpness and vary considerably in the number of inclusions 

contained within them. One long crystal of irregular shape was 

observed to be a veritable sponge, inclosing glass and inicrolites of 

plagioclase and augite. The groundinass is hyalopilitic and contains a 

little carbonate scattered through it.

A specimen (.1945 S. IST.) from the portion of the flow 1 mile northeast 

of McKay's mill, shown in PI. IV, also 'has somewhat smaller plagioclase phenocrysts than usual, and resembles in megascopic character 

the Dardanelle flow, which lies above it, separated by the biotite-augitelatite. Under the microscope, however, it shows no marked difference 

from other thin sections from the same flow. There are the same large 

labradorites mottled with glassy inclusions and showing albite twinning lamelliB combined with those of the Carlsbad and pericline laws. 

Angite is present in large, irregular pheuocrysts and in smaller crystals 

Avith idiomorphic cross sections transverse to the prism. Olivine is 

distinctly less abundant and occurs in smaller crystals than in that 

portion of the flow near Shaws Flat already described. In this particular slide it has been almost wholly altered to serpentine, a rather 

uncommon condition in the Table Mountain flow. The groundmass is 

finer, less opaque, and typically hyalopilitic.

Across the north fork of the Stanislaus the small area 1£ miles east 

of Squaw Hollow presents a thoroughly typical facies (1913 S. K.), both 

megascopically and microscopically. The large labradorites frequently 

show Carlsbad twins and give extinction angles corresponding to the
32 LAVA FLOWS OF THE SIERRA NEVADA. [BULL.89.

mixture Ab3An4 . They sometimes show deep and intricate einbayments, and are full of the usual inclusions. The augite occurs in characteristic phenocrysts and also as small grains, which are sometimes 

heaped together in a manner suggesting the aggregates formed by the 

magmatic resorption of hornblende in many audesites. Like the Shaws 

Flat facies described by Turner, the glassy base is dark and semiopaque, and the slide contains small irregular patches of greenishyellow serpentine. The latter does not show definite outlines, and is 

not a pseudomorph after any crystalline mineral. It permeates portions of the slide irregularly, and may "fill some small vesicles. Augite 

and olivine are less abundant than in the Shaws Flat rock, the latter 

mineral occurring only in small crystals in the groundmass.

The small mass (1794 S. jST.) resting upon the andesitic breccia 2 miles 

northeast of Ashcraft's is megascopically halfway between the typical 

facies of the Table Mountain and Dardatoelle flows. Under the microscope it shows an equally intermediate character, and may possibly 

belong to the latter flow. The labradorite (Ab3An4 ) phenocrysts are 

fresh and sharply twinned, pericline lamellae being not uncommon. 

They show the basal and brachypinacoidal cleavages in systems of 

fine cracks, and are comparatively free from inclusions. The other 

phenocrysts are augite, magnetite, and oliviue, lying in a hyalopilitic 

grouudmass with considerable globulitic glass.

As the lava showing the spheroidal forms seen in PI. VIII has been 

subjected to chemical analyses, it will be described somewhat at length. 

Megascopically the rock (1422 S. N.) forming these spheroids is indistinguishable from specimens collected from the Tuolumue Table 

Mountain, 40 miles to the southwest. It shows similar tabular phenocrysts of labradorite, with here and there an irregular crystal of augite, 

lying in a compact dark groundmass. The plagioclases are fresh and 

glassy, and their glistening cleavage planes are the most conspicuous 

features of the freshly broken rock, and even of the natural surfaces, 

for the weathering has been but skin deep. A common size for these 

phenocrysts is. about 2 by 7 by 9 nim, the plane of greatest extension 

being the brachypiuacoid. They invariably show the albite twinning 

on the basal cleavage planes, and not uncommonly Carlsbad twinning 

also.

Under the microscope the thin section (PI. XI, A) shows the usual 

phenocrysts of labradorite and pale-greenish augite with small idiomorphic olivines, lying in a very fine, even groundmass, which is 

typically hyalopilitic, showing flow lines of the small lath-shaped microlites around the phenocrysts. The large labradorites show the usual 

rounded and embayed outlines, and are mottled with abundant inclusions. The latter are usually similar to the glassy base of the rock, 

but more rarely a greenish serpentinoid substance. Some of the 

labradorites have been broken in the magma and the parts displaced, 

and angular fragments, probably of similar origin, are common. The
BULLETIN NO. 89 PL. X

POINT TO THE SOUTH, LOOKING OVER THE CANYON OF THE MIDDLE STANISLAUS RIVER.

Photograph by H. W. Turner.
PLATE XI

Bull. 89 3 '

33
PLATE XI.

MICROSECTIONS OF LATITES (SEMIDIAGEAMMATIC).

A. Augite-latite (1422 S. N.), Table Mountain flow, showing general structure of the 

rock, with phenocrysts of labradorite (Lb), augite (A), olivine (0), and magnetite.

B. Biotite-augite-latite (1955 S. N.)> showing eutaxitic or "piperno" structure. 

The drawing shows phenocrysts of labradorite (Lb), augite (A), biotite (B), 

hornblende (Hb), and magnetite, with included rock fragments, lying in a 

banded and partially brecciated microlitic glass.

34
U. S. GEOLOGICAL SURVEY BULLETIN NO. 89 PL. XI

MICROSECTIONS OF LATITES fSEMIDIAGRAMMATIC).
IIANSOME.] TABLE MOUNTAIN FLOW. 35

plagioclases show the usual combination of albite and Carlsbad twinning, with occasional pericline lamellae. A determination of the extinction angles by Michel Levy's method indicated a labradorite with the 

composition Abi An,. The specific gravity of a small, apparently pure 

fragment was found by means of Thoulet solution to be 2.648, which 

is rather light for apparently so basic a plagioclase. The augite, which 

is much less abundant than the labradorite, is very pale green in color, 

nonpleoehroic, and identical, with that already described. Sharply 

idiomorphic cross sections of the prism zone are rather more common 

than usual. It is frequently twinned polysynthetically on the orthopinacoid in the usual manner. The olivines are fairly abundant, but 

small. They are generally fresh, and show crystallographic outlines, 

but in somes cases they are changed to yellow serpentinous pseudoniorphs. The groundmass around these olivine crystals is sometimes 

distinctly more finely crystalline than elsewhere, giving them the 

appearance of being surrounded by a faint halo. Some scattered 

crystals of magnetite are of sufficient size to be included among the 

phenocrysts.

The groundmass is truly hyalopilitic, and is made up of small slender 

feldspar, microlites, minute crystals of magnetite, and globulites, all 

lying thickly crowded in a clear glass of faint brownish-violet tint. 

The microlites are often so crowded that it is difficult to find a portion 

of the section that will show no double refraction between crossed 

nicols. By using an immersion objective, however, and working on the 

thinnest edges of the section, it is possible to differentiate the glassy 

matrix from the feldspar microlites and to see that it is full of crystals 

of magnetite, ranging from those that show crystal outlines down to 

barely visible black specks. Associated with the magnetite grains 

are numerous globulites and globulitic granules of high relief and faint 

green tint, which are probably augite. From this it appears that magnetite, although not conspicuous with low powers, is yet quite abundant 

in the mass of the rock. Augite, also, is probably a more important 

constituent than would be indicated by its distinct crystals.

The feldspar microlites are generally too small to be determined optically, but the better-individualized ones generally show albite lamella 

with an obliquity of extinction corresponding to labradorite. Apatite 

occurs in rather stout, sharply hexagonal prisms.

A chemical analyses of this rock is given in Column III of the table 

of chemical analyses on page 58. Its specific gravity is 2.67, which is 

lower than one would usually expect in a rock of such dark color and 

compact texture.

A few hundred yards to the east of the spheroidal facies the bottom 

of the Table Mountain flow is exposed, resting upon clastic andesitic 

beds, as shown in PI. V. The flow is here exceedingly vesicular in 

its lower portions, the large labradorite phenocrysts being held together 

by a paste of frothy red glass. The microscope shows the usual labra-
36 LAVA FLOWS OF THE SIERRA NEVADA. [BULL. 89.

dorite pheuocrysts fnll of glass inclusions. Augite was observed only 

as an inclusion in one of the labradorites. The cementing material is 

a vesicular, semiopaque brown glass, with a few labradorite microlites. 

The turbidity of the glass is apparently due to the oxidation of the 

magnetite, contingent upon the highly spongy character of the rock. 

The inclusions in the large plagioclases are of the same glassy nature 

as the matrix, while in other occurrences already described the inclusions consist of more or less individualized groundmass, thus indicating that crystallization went on in the included portions as well as in 

the groundmass outside the labradorite phenocrysts.

At the West Dardauelle the latite of the Table Mountain flow (1023 

S. jST.) is niegascopically identical with the spheroidal facies (1422 S. N.) 

just described, although its larger structure is columnar. Microscopically it resembles rather more closely the sections from the Table Mountain near Sonora, although with considerably less olivine. The large 

labradorites give extinction angles corresponding to a mixture Ab t An t. 

They are full of inclusions of glass, with sometimes small crystals of 

augite and labradorite. The augite phenocrysts are larger and more 

abundant than usual. They are sometimes, like the labradorites, filled 

with inclusions, plagioclase laths and small patches of yellow serpentine being among the latter. The thin section also shows serpentinous 

patches like those described in the Tuolumne Table Mountain specimens. Olivine, however, is not so abundant, being confined to small 

idioinorphic crystals scattered through the groundmass. These are 

generally fresh, but are sometimes partly changed to serpentine.

A specimen (1030 S. K.) taken near the -upper surface of the flow is 

rendered spongy by abundant small vesicles. Under the microscope it 

shows the same phenocrysts as the preceding rock, but the labradorite 

microlites in the groundmass are much smaller, and the rock as a 

whole is more glassy. With high power the glass is seen to be thickly 

dusted with magnetite and globulites and to show the faint violetbrown tint characteristic of the perfectly fresh glass of these rocks. In 

spite of the freshness of the other constituents, the olivine has all been 

altered to yellow serpentinous pseudomorphs.

The microscopic petrography of the Table Mountain flow has been 

described at some length on account of its interesting chemical character, and for the reason that such, a course seemed desirable in dealing 

with a flow so greatly dissected. It is seen that in its superficial 

appearance and in the presence of olivine the augite-latite iresembles 

the basalts; in the character of the augite and plagioclase, in the 

degree of preponderance of the feldspathic constituents, and in the hyalopilitic structure of the groundmass, it is more closely related to the 

audesites; lastly, in the fine dissemination of the magnetite, in the 

abundance of microtine phenocrysts, and, above all, in chemical composition, it shows certain analogies with the trachytes. No potash feldspar has been detected in any of the thin sections studied, except,
KANSOME.] BIOTITE-AUG1TE-LATITE. 37

possibly, as a very narrow fringe on some of the labradorite phenocrysts, 

and even thjs seems to be the exception rather than the rule.

THE BIOTITE-AUGITE-LATITE.

As already indicated in the account of its occurrence, considerable 

difficulty was experienced in deciding whether this volcanic rock was 

a true flow, like the Dardanelle flow above it and the Table Mountain 

flow beneath it, or whether it should be classed as a tuff. In spite of 

the fact that it frequently shows the presence of fragmental material 

the rock is regarded as constituting a flow, for reasons that can be 

better appreciated after a petrographical description.

The facies occurring within the drainage of Love Creek, about 3 miles 

south of Big Trees post-office, is a thoroughly typical one. A specimen 

(1882 S. N.) taken just north of the road, about a mile southwest of 

McKay's, shows a bright-gray rock, that sparkles brilliantly on fresh 

surfaces, from the numerous crystals of biotite. In contrast to the' 

Table Mountain augite-latite upon which it lies, this rock has a harsh 

or trachytic feel and is somewhat porous. Besides the'biotites, the 

fine, and evidently glassy, groundmass'holds small phenocrysts of 

clear sanidine-like feldspar and fragments of dark glass and of glassy 

volcanic rock. Some of the black glass inclusions are irregular and 

somewhat angular in outline, while others appear to be drawn out into 

thin lenses. These lenses, together with the biotite crystals, have a 

tendency to lie horizontal, so that the lava cleaves most readily along 

a plane parallel with the top and bottom of the flow. This arrangement 

is by no means universal, however, for the biotite tablets are found in 

all positions. These latter are from 1 to 2""" in breadth and sometimes 

0.5""" in thickness. They have sharp crystallographic boundaries, the 

narrow planes of the prism and clinopiuacoid reflecting the light nearly 

as brilliantly as the basal planes.

The thin section shows that the greater part of the rock is made up 

of a light-brown glass, with a suggestion of violet in its peculiar tint. 

Scattered about in this glassy matrix are abundant phenocrysts of 

plagioclase and biotite, a few broken or irregular crystals of augite, 

crystals of magnetite and apatite, and fragments of more or less glassy 

volcanic rocks.

The plagioclases usually show beautifully sharp twinning in accordance with the albite law, and some show both albite and Carlsbad twin 

ning, with occasional pericline lamelhe. The Carlsbad-albite twins 

give extinction angles corresponding to labradorite of the composition 

Ab3 An4 . There is no sauidine present, and the index of refraction of all 

the plagioclase, as determined by Becke's method, is distinctly greater 

than the balsam of the slide, which is about 1.540. The outline of the 

plagioclases is sometimes irregular and angular, sometimes rounded, 

and sometimes in part defined by crystallographic planes.

The biotite is abundant and in sharply bounded hexagonal tablets.
38 LAVA FLOWS OF THE SIERRA NEVADA. [BULL.89.

It is bright chestnut brown, with the usual strong absorption and small 

axial angle. It frequently includes prisms of apatite. «,

Augite is not abundant, and rarely shows crystallographic outlines. 

It is very pale green, and in no way distinguishable from that in the 

Table Mountain flow, already described.

A green hornblende is quite charactistic of this rock, occurring in - 

nearly every slide of the biotite-augite-latite, but always in strictly 

accessory amount. It is usually in small shreds or irregular fragments, 

of which not more than two or three are found in any single thin section. In only two cases were prismatic cross sections seen with anything like idiomorphic outline, the best of these being shown in PI. XI, 

B. The optical orientation is: a = a, fr = &, and jc: c = at least 11°. The 

pleochroism is: a, faint yellow; ft, dark brownish green, and c, dark 

green. The absorption is: a< ft< £.

Magnetite occurs in good-sized grains in the glass, sometimes attached 

to the anhedra of labradorite and augite, and frequently including 

prisms of apatite. The latter mineral also occurs isolated in the brown 

glass in well-developed prisms.

The sharply bounded rock inclusions, as seen in the slide, are usually 

of small size, less than 0.5 mm in diameter, and rounded in outline. 

They consist of fragments of andesitic or latitic groundmass, generally 

indistinguishable, in such small areas, from facies of Table Mountain 

and Dardanelle flows. They sometimes contain phenocrysts of labradorite like those occurring in the inclosing rock. The glass base of 

these inclusions is usually gray and globulitic, but sometimes clear and 

pale brown, like that making up the mass of the section. In one case 

a rounded inclusion was observed with a central portion composed of 

labradorite microlites and gray glassy base, and a peripheral zone of 

similar microlites lying in a clear, light-brown glass.

An examination of the isotropic matrix which makes up the mass of 

the rock shows it to be by no means homogeneous. It is a confused 

mixture of shreds and strings of light-brown, translucent glass, with 

other portions which are rendered dark and turbid by microlites and 

globulitic dust. Sometimes these lighter areas are sharply bounded 

and resemble inclusions, at other times they fray out imperceptibly into 

the groundmass, or are drawn, out in long flamboyant tongues. Some 

of the ligh|;-brown patches contain plagioclase microlites, and such portions are not always sharply separated from the nonmicrolitic areas. 

The whole aspect of the thin section suggests that the development of 

a fluidal structure was followed by flow brecciation on a minute scale, 

giving as a result a rock that is in some respects not unlike a tuff. 

That the rock is not an ordinary tuff is indicated by the close affinity 

shown between the inclusions and the including matrix, by the absence 

of distinctly foreign material, by the inclusion within areas of homogeneous brown glass of labradorite phenocrysts exactly like those which 

occur in the finely brecciated portions, and, lastly, by inclusions of the 

same light-brown glass within such phenocrysts.
RANSOME.] BIOTITE-AUGITE-LATITE. 39

On the supposition that the rock, if a clastic tuff, must owe its present induration to the presence of a considerable proportion of opal 

among the isotropic material, a weighed portion of the finely powdered 

rock was boiled in a platinum dish for two hours with a 10 per cent 

solution of sodium carbonate. The dish was allowed to stand for nineteen hours, again heated, the liquid filtered off, and the silica determined in the usual way. The amount soluble under these conditions 

was only 1.6 per cent.

A specimen (1877, S. K.) from the couMe-like mass half a mile north of 

McKay's, already described, is slightly darker in color than the foregoing, and, while plainly containing inclusions, has every appearance, 

both in the field and in the hand specimen, of being a glassy lava and 

not a tuff.

At first glance the thin section looks tuffaceous, but closer examination shows that the shreds of violet-brown glass, instead of behaving 

as rigid clastic fragments, frequently curve around the phenocrysts and 

inclusions in well-marked flow lines, or conform to their shape. The 

glass has a rather more distinct violet tint in this section, and is a little 

more abundant, than in the one just described. There is also a little 

more augite. The specific gravity of the rock is 2.47.

One mile northeast of McKay's, on the river slope of the ridge, 

the biotite-augite-latite (1944 S. K.) resembles megascopically that first 

described (1882 S. ST.), but shows many long-drawn-out lenses of dark 

glass. Under the microscope it shows comparatively few phenocrysts 

or inclusions and a large proportion of the faint violet-brown glass. 

One small fleck of green hornblende occurs in the slide.

The latite of the elliptical area (1977 S. ]$.) shown on the map 1£ 

miles a little west of south from Fennessy's, and overlain by andesitic 

breccia and tuff', is light gray in color, with a somewhat more earthy 

texture than usual, and less biotite. Under the microscope it shows 

the usual characteristic features, although the biotite is not quite so 

abundant. There are a few fragments of the green hornblende present. 

The shreds of pale-brown glass show some flow structure and are bent 

around the phenocrysts and included fragments.

A specimen (1955 S. N.) taken near the southern end of the inclosed 

area of granite, about halfway between Fennessy and Clover meadows, 

is a light-gray facies with abundant feldspar phenocrysts, but not much 

biotite. In thin section (PI. XI, B} this rock appears thoroughly typical. The glass, which makes up the greater part of the slide, is brown 

and turbid, but shows eutaxitic banding, with excellent flow structure. 

In this glass lie the phenocrysts of plagioclase, biotite, and augite, Avith 

the usual fragments of volcanic rock. The plagioclases are twinned 

with beautiful sharpness, and several readings on albite-Carlsbad twins 

indicated a labradorite a trifle more basic than Ab:j An4 . The biotite is 

rather more abundant than the hand specimen indicates, and occurs in 

the usual tablets with inclusions of apatite. The augite occurs sometimes in isolated fragments, or anhedra, and sometimes intergrown
40 LAVA FLOWS OF . THE SIERRA NEVADA. [BULL. 89.

and partly surrounded by the labradorite crystals. One sharply idiomorphic section of the green hornblende occurs in the slide, being cut 

transverse to the prism and showing the usual amphibole outline and 

cleavage. Magnetite is in crystals and aggregates up to 0.5 mm in 

diameter, and, like the augite and biotite, frequently includes apatite 

crystals.

At a point 3f miles southwest of Clover Meadow, and a little over 1 

mile west of the bold spur marked 7100 (feet) on the map, occurs a 

dark-gray facies (1420 S. K), with the usual phenocrysts of microtine 

and biotite. It contains small rock fragments, but has on the whole 

the appearance and consistency of a lava rather than a tuff. The 

microscope shows the usual structure of these rocks, with the characteristic brecciattd eutaxitic glass. The latter is brown and more turbid than is generally the case, and is probably somewhat weathered. 

Phenocrysts of feldspar are fairly abundant. They are sometimes 

broken and angular and occasionally slightly embayed, but they often 

preserve their original crystallographic outlines. Combination twins, 

according to both albite and Carlsbad laws, are common, and the plagioclase is labradorite. The phenocrysts are generally rather free from 

inclusions, and show the basal and brachypinacoidal cleavages 

unusually well. The other phenocrystic minerals are biotite, augite, 

and magnetite. Apatite occurs in small prisms included in all the 

other minerals.

Some of the bands and shred-like patches of brown, glass show a 

striking mottled appearance, produced by thickly crowded round spots 

of shadowy outline, surrounded by darker-brown rims. The lighter 

central portions of these spots show an obscure radial arrangement, as 

if from a very imperfect spherulitic structure. No distinct microlites 

can be made out, however, although there is some slight double refraction between crossed nicols. The usual inclusions of latitic (?) groundmass with lath-shaped plagioclases occur in this facies, but the character of the surrounding matrix, with its fluxion phenomena, precludes 

the idea of the rock being a tuff. An analysis of this facies is given 

on page 58, Column VI of th'e table.

A mile southwest of the little pond in Clover Meadow is a remnant 

of the biotite-augite-latite (exaggerated on the map), resting upon the 

andesite breccia. It is very similar in appearance to the facies just 

described,, but shows marked flow structure, which is brought out by 

atmospheric etching on exposed surfaces. Long-drawn-out and parallel 

lenses of nearly black glass are noticeable in the hand specimen (1948 

S. K.). Under the microscope it is noteworthy for its fine large phenocrysts of labradorite (Ab3An4 ) and biotite and the wavy and contorted 

areas of clear, light-brown glass. Augite is also present among the 

phenocrysts, and, what is not known elsewhere in this rock, a.few 

crystals of orthorhombic pyroxene and some scattered grains of olivine. 

The orthorhombic pyroxene occurs in stout prisms, rounded at the
HANSOUB.] BIOTITE-AUGITE-LATITE. 41

ends, and up to 0.5 mw in length. It is distinctly pleochroic, with 

strictly parallel extinction and low double refraction, and is readily 

distinguished from the pale-green, nonpleochroic augite. It is probably 

enstatite or bronzite, and it appears to be identical in pleochroism 

and double refraction with, the orthorhoinbic pyroxene in the so-called 

enstatite-porphyrite of the Cheviot Hills. The divine is in small 

irregular grains, and not abundant.; but its presence is interesting, as 

it is rare to find biotite, orthorhorabic pyroxene, and oliyine all present 

in nn effusive rock of intermediate composition. The green hornblende, 

frequently referred to as a characteristic accessory in the rock of tliis 

flow, occurs both in the glassy part of the section and in one of the 

included volcanic Iragments. There are also present the usual prisms 

of apatite and a little magnetite.

The large labradorites are often intergrown with the augite, showing 

that the latter mineral is the younger. All the pheuocrysts occur both 

in the clear brown glass and in the turbid, confused, and microlitic 

matrix between the clearer streaks. The apatite is° included in the 

glass and in all the larger phenocrysts save the olivine. The more or 

less rounded fragments of volcanic rock in the. section are plainly 

locally inclusions, but they show a mineralogical resemblance to the 

rock in which they are inclosed and may not have been derived from a 

wholly foreign source. Some of them show only very small feldspar 

rnicrolites embedded in a brown glass like that so abundant in the 

inclosing rock. One compound inclusion was noted which consisted of 

several small rounded fragments of microlitic brown glass inclosed 

in a similar fine groundinass of slightly different color. This strongly 

suggests that the greater part of the inclusions in the biotite-augitelatite are not foreign material, but represent portions of the magma, 

which, having attained a certain degree of crystallization, Avere brecciated by the movement of the lava stream and disseminated through, 

its more glassy portions.

A specimen (1.435 S. N".) from the ridge just south of Clover Meadow 

is a light-gray rock with phenocrysts of biotite and microtine and small 

rounded fragments of volcanic rock, lying in'a fine light-gray and somewhat porous grouuclmass. This is probably the most tuffaceous facies 

in external appearance of the whole flow, tinder the microscope it 

shows the usual pheuocrysts of labradorite, biotite, and augite in a 

matrix made up of light-brown glass. The proportion of glass in the 

slide is larger than usual and has a fine shred-like character. It would 

perhaps be impossible to determine satis!actorily from a microscopic 

examination of this slide whether it should be classed as a tuff or not. 

Some of the shreds of glass, however, are molded to the form of the 

phenocrysts. A small fragment of green hornblende was observed 

isolated in the glass, while another crystal, partially resorbed and surrounded by a dark granulated border of augite and magnetite, was seen 

in one of the fragmental inclusions.
42 LAVA FLOWS OF THE SIERRA NEVADA. [BOLL. 89.

An inclusion (1436 S. N.) of much larger size than any observed by 

me was found by Mr. H. W. Turner in the biotite-augite-latite just 

described. It measures about 6 cm in diameter and is rather angular in outline. It is a hard, compact rock, light gray in color, showing 

small phenocrysts of plagioclase and augite, and is apparently an andesite. Under the microscope it shows phenocrysts of plagioclase, augite, 

and orthorhombic pyroxene, with moderate-sized grains of magnetite, 

lying in a very fine hyalopilitic groundmass. The plagioclases are 

labradorite, apparently a little more basic than Ab:) An,,. The albite 

twinning is not so regular as in the latites, and the combination 

with the Carlsbad law not quite so frequent, bat with the. pericline 

law more so. They frequently show zonal structure with undulatory 

extinctions, especially in bra'chypinacoidal sections. The phenocrysts 

are usually,small, few in the section being over I 1 ""1 in length.

The orthorhombic pyroxene occurs in nearly colorless crystals of 

prismatic habit up to about 0.75 Inm in length, usually with more or less 

rounded or irregular ends.. Cross sections of the prism show rectangular outlines with slightly truncated corners, due to the dominant 

development of the brachypinacoid and macropiuacoid. The prismatic 

cleavage is well developed, while the macropiuacoidal cleavage is indicated only by a few fine cracks. The extinctions are always parallel to 

the traces of the pinacoids. Sections transverse to the prism show the' 

emergence of a bisectrix, with a large axial angle. By comparison with 

the interference figures given by longitudinal sections, and by using 

the method given by Michel LeVy, 1 it was determined that this is the 

acute bisectrix. The optical orientation is: a = a, & = Ii, and c = jc. 

The mineral is therefore optically positive. The index of refraction is 

not noticeably different from that of the monoclinic pyroxene in the 

slide, but the double refraction is much lower, ranging from gray to 

pale straw-yellow. The pleochroism is distinct: a = very pale brown 

ft = very light yellow, and .c = pale green.

From the foregoing description it is seen that the pyroxene has the 

optical orientation of enstatite or bronzite; but the distinct pleochroism and large axial angle point rather to bronzite than to enstatite.

This inclusion is accordingly a bronzite-augite-audesite, identical 

with specimens that will be described from the underlying andesitic 

breccia, and was probably caught up (with other similar ones noted at 

the same locality) by the latite from the clastic beds over which it 

flowed.

The general microstructure of the biotite-augite-latite appears to 

approach very closely to the eutaxitic structure as the term was first 

employed by Fritsch and Eeiss,2 who applied it to certain facies of 

phonolites, andesites, and trachytes possessing some resemblances to

1 Les min6raux des roches, Paris, 1888, p. 95.

2 Geologisohe Beschreibung der Insel Teneril'e, Wintertliur, 1868, pp. 414-422; also abstract in 

Neues Jabrbuch fiir Hin., etc., 1868, pp. 752, 849-852.
RANSOME.] EDTAXITIC STRUCTURE. 43

clastic rocks and inclosing undoubted clastic fragments. They distinguished agglomerate lava, in which the structure was supposed to be 

due to a partial refusion of clastic material, from piperno, in which portions of the magma in different stages of crystallization are brought 

into juxtaposition by the motion of the flow. Common usage, however, 

has somewhat altered the original application of the term eutaxitic, so 

that it frequently implies merely a fluidal banding brought about by 

alternating streaks of microfelsitic and clear glass, 1 or is even used as 

"a general name for banded volcanic rocks." 2 That such can hardly 

have been the earlier application of the word appears from the discussion that has centered about the original piperno of Pianura in the 

Phlegrsean Fields, near Naples, a rock that Fritsch and Reiss took as 

the second type of eutaxitic structure, and which appears to resemble 

in some ways the biotite-augite-latite of California. Luigi dell' Erba :1 

considers this rock a tuff, but the greater number of petrographers 

have regarded it as a lava flow. Zirkel 4 refers to it as a sanidine trachyte with eutaxitic structure, remarking 1 hat Luigi dell' Erba's view 

is not even probable, while Rosenbiisch 5 cites it as an example of his 

Pouza type of the trachyte family. Such a discussion could scarcely 

have arisen were the structure concerned a simple banding such as is 

observed in many vitrophyres, and which no petrographer could for a 

moment regard as indicating a tuff'aceous origin. Kticli,6 following the 

terminology of Reiss, describes both kinds of eutaxitic structure, the 

agglomerate lava and the piperno, as occurring in the dacites and audesites of Colombia. The latter form is particularly abundant, and Kiich 

remarks that it is at times impossible to distinguish the two varieties, 

as the piperno often contains included fragments of other andesites. 

Wichinanu,7 in describing an augite-inica-andesite from the Indian 

Archipelago having a structure apparently nearly identical with that 

of the biotite-augite-latite of the preceding pages, refers to it as 

having piperno structure; and there seems to be little doubt that this 

latter name, as used by the petrographers cited, expresses accurately 

the structure of the second flow of the Sierra Nevada latites.

When, on the other hand, a thin section of the last-named rock is 

compared with that of a lava having typical flow banding as, for 

example, the beautiful vitrophyre of San Lugano, in the Tyrol, or the 

pitchstone-vi trophy re occurring between Lake Lugano and Lago Maggiore, both of which, according to Rosenbusch," often show eutaxitic

1 Zirkel, Fetrographie, 3d ed., Vol. I, 1893, p. 405.

JKemp, Handbook of Kocks, New York, 1890, p. 130.

?Giornal di Miuoralogia, etc., Vol. Ill, 1892, pp. 23-54.

'Loc. cit., Vol. II, p. 790.

"Mikroskopische Physiographic, 3d ed M Vol. II, 1896, p. 706.

'Geologische Studieu in der Eepublik Colombia, I Petrographie, 1. Die vulkanischen Gesteine, 

Berlin, 1892, pp. 84-86.

'Petrographische Studien iiber den indischeu Archipel, abstract iu Neues Jahrbuch ftir Min., etc., 

1897, Vol. I, p. 283.

»Loc. cit., p. 698.
44 LAVA FLOWS OP THE SIERRA NEVADA. [BOLL.89.

fades the chief difference seems to lie in a greater irregularity and 

brecciation of the bands in the latite, and in the presence of included 

rock fragments.

In looking over the large collection of volcanic rocks brought from 

Asia Minor by the Assos Expedition, and now at Harvard University, 

it was found that the peculiar structure of the biotite-augite-latite was 

exactly reproduced in a specimen (A. E. 310) from near the Hot Springs 

of Tonzla, in the southwestern part of the Troad. This specimen, as 

Mr. J. S. Diller very kindly informed the writer, ''belongs to the lower 

portion of a flow of rhyolite, near its contact with the underlying tuff. 

The rhyolite some distance away from the contact is deep flesh red. 

Near the contact it is frequently black and glassy, inclosing many 

fragments of the tuff over which it flowed." The hand specimen shows 

a light-gray, very glassy rock, with streaks of dark glass and abundant angular glassy inclusions of light-buff color, together with small, 

slightly rounded volcanic fragments, resembling superficially those in 

the latite.

Under the microscope the similarity of structure is remarkable. The 

light-brown glassy streaks, alternating with microlitic patches, show 

the same confused and brecciated appearance as in the latite. Phe* 

nocrysts of biotite and feldspar are abundant, and there are numerous small rounded inclusions of some andesitic rock. The structural 

resemblance between the Touzla rock and the biotite-augite-latite is so 

close that only a critical investigation of the phenocrysts and inclusions would serve to distinguish an nnlabeled thin section of the former 

from one of the latter. To make the resemblance still closer, no sanidine was seen in the Asia Minor rock, all the pheuocrysts in the thin 

section being plagioclase (audesine or labradorite).

Another specimen (A. E. 531) which, according to Mr. Diller, is from 

"one of the large flows of rhyolite forming the plateau that lies between 

the Touzla River and the southern coast of the Troad, west of ASSOS," 

shows a very similar structure, while specimens from near Baba-galessi 

(A. E. 559 and A. E. 560) exhibit gradations into nearly or quite typical 

unbrecciated flow-banding.

The object of this comparison is not to show that these specimens 

from the Troad are chemically or miueralogically identical with the 

biotite-augite-latite, but merely to draw attention to their structural 

identity, and the fact that they occur as true flows and not as tuffs.

As an historical illustration of the difficulty that sometimes exists in 

distinguishing a tuff from a massive lava may be recited the case of 

the so-called "peperino" near Viterbo, in Italy, which, according to 

Washington,1 is probably a tuff, although it possesses some apparent 

flow structures, and has been by earlier investigators frequently designated a massive rock.

There has been mentioned the occurrence near Mill Creek of a vitro1 Italian putrolojjical sketches, II: J our. Geol.,. Vol. IV, 189G, pp. 838-840.
BAHSOMB.] BIOTITE-AUGITE-LATITE. 45

phyric lava which, though underlying some augite-latite belonging 

apparently to the Table Mountain flow, yet resembles the biotiteangite-latito that usually rests upon the latter flow. Megascopically 

this rock (1866 S. N.) is a gray, extremely brittle glass with a pitchstonelike luster. It is speckled with a few minute feldspar pheuocrysts and 

shows streaks of black glass and also lighter-colored glassy patches 

resembling inclusions.

Under the microscope the thin section, consisting chiefly of pale 

violet-brown glass, shows the eutaxitic structure already fully 

described, but, as might be expected from the megascopic appearance 

of the rock, approaches a little more nearly the ordinary flow structure 

of the vitrophyres. This glass contains numerous angular (rarely 

rounded) fragments of labradorite (Ab3An.,), less abundant anhedra 

of pale-green augite, a few flakes of biotite, and an occasional prism of 

orthorhombic pyroxene. Most of the slides examined also show one or 

two shreds of green hornblende. Apatite occurs in small prisms, 

especially as inclusions in the augite, and there are also a few grains of 

magnetite present. Like the typical biotite-augite-latite, this facies 

frequently shows small rounded inclusions of volcanic rock consisting 

of small microlites of plagioclase in a glassy base, but it differs from 

all the known occurrences of the former in being more glassy and in 

the paucity of biotite. A chemical analysis of this rock will be found 

in Column YII of the table of analyses on page 58; it will be seen to 

have more silica, and less lime, magnesia, iron oxides, and alumina, 

than the other'latites.

Immediately above the facies just described, and also at Clover 

Meadow, is a rather peculiar lava (1867 S. 1ST.'and 1428 S. IsT.) of light 

brick-red color, containing a few small empty cavities, but of generally 

compact texture and speckled with small phenocrysts or fragments of 

glassy feldspar. In its general aspect the rock is rhyolitic, although 

differing from the ordinary white rhyolites of the district, which, as far 

as known, are all older than any of the andesitic breccias. Under the 

microscope the rock shows phenocrysts of feldspar, frequently broken 

and angular, with occasional flakes of biotite, lying in a reddish, turbid, microfelsitic groundmass. The feldspars are all plagioclase, and 

some of the-sharply twinned individuals give extinction angles indicating labradorite as basic as Ab3An4. The matrix in which they lie 

has its original structure obscured by secondary silicification and by 

the separation of ferric oxide, but appears to show some remnants of 

the vitrophyric structure observed in the preceding rock. There are 

apparently the same patches of bent and contorted glass, with occasional small rounded inclusions of volcanic rock. A partial chemical 

analysis of this red lava is given in Column IX of the table of chemical 

analyses, page 58. It is higher in silica than any of the latites, but 

too low for a typical rhyolite. The amount and relative proportions of 

the nlkalie.s, too, give no very definite information as to its proper posi-
46 LAYA FLOWS OF THE SIERRA NEVADA. [BULL. 89.

tion, and it is uncertain whether it should be classed as a somewhat 

weathered superficial portion of the vitrophyric latite below it, or 

whether it is a very thin flow belonging rather with the rhyolites. The 

former supposition, however, seems much more probable, as in the 

latter case it would indicate a rhyolitic eruption of much later date 

than that of the normal white rhyolites and rhyolite tuffs which lie at 

the base of the whole .Neocene volcanic series. For this, however, 

there is no evidence other than the two widely separated and insignificant patches of red lava just described, which is certainly not a typical 

rhyolite, and does resemble the rather acid latite (1866 S. K.) just 

beneath it.

THE DARDANELLE FLOW.

The rock of the youngest of the three flows resembles very closely 

that of the oldest or Table Mountain flow, and this resemblance is in 

a few cases so close that it would be impossible to say to which flow a 

given hand specimen belonged. Considered in their typical development, however,- the two facies are fairly distinct. The augite-latite 

(1260 S. K), forming the extreme summits of the West Dardanelle, 

may be taken as a typical facies of the Dardanelle flow. This is a 

dense, nearly black rock, ringing clearly under the hammer and breaking with a clean, slightly conchoidal fracture. The broken surfaces 

show clear glassy phenocrysts of plagioclase, resembling those 01 the 

Table Mountain flow, but smaller, sharper, and less abundant. Their 

basal cleava'p'e faces show albite lamellae, frequently combined to form 

Carlsbad twins. Close inspection will generally reveal a few small 

phenocrysts of augite, but the plagioclases are the only conspicuous 

megascopic crystals. They lie in a very compact, nearly black groundmass, in which a good lens can detect only a few feldspar microlites.

The microscope shows pheuocrysts of labradorite. augite, and olivine, 

with apatite arid magnetite, lying in a light-brown hyalopilitic groundmass. The labradorites are the largest and by far the most abundant 

phenocrysts iu the slide, but are rarely more than 5mm in length. They 

are fresh and sharply twinned, but often carry inclusions of glassy 

base, much as do the larger phenocrysts of the Table Mountain flow, 

and occasionally include small augites. They are usually tabular 

parallel with the brachypinacoid, and the prevailing section is lathshaped. Observations on albite-Carlsbad twins by Michel LeVy's 

method gave extinction angles indicating a labradorite of the composition AbiAnj. The outlines of the phenocrysts are generally sharper 

and less embayed than in the Table Mountain flow.

The augite is identical with that in the latter flow, but is in smaller 

crystals and shows a greater tendency toward sharpness of crystallographic outline, especially in the prism zone.

The olivine occurs usually in idiomorphic crystals of small size scattered through the groundinass, but occasionally oue of larger size is 

met with
KANSOME.] DABDANELLE FLOW. 47

The hyalopilitic groundmass shows sharp, clear feldspar microlites, 

with more or less flow structure, lying in a light-brown glass. These 

plagioclases usually show albite twinning with extinction angles corresponding to labradorite. Bifurcated ends are common. The brown 

semiopaque glass is quite abundant, and makes up a considerable part 

of the section. It shows a rather noticeable fin3 mottling, suggesting 

an incipient spherulitic structure and apparently produced by the 

crowding together of very minute brown globulites. The magnetite, 

instead of being minutely disseminated through the glass, as is common 

in these rocks, forms small crystals and aggregates readily seen with 

low power.

The specimen just described was taken from the highest point of the 

peak. A second (1024 S. K.) from near the bottom of the same flow was 

very similar in .thin section, but is slightly weathered. The glass is 

gray instead of brown, is finely globulitic, and has the magnetite a 

little more finely disseminated. Apatite, in small prisms, occurs in 

both slides.

A hand specimen (1421 S. K) from the summit of the ridge, one-half 

mile east of Clover Meadow, is megascopically identical with that just 

described. Under the microscope the chief differences to be observed 

are a more pronounced flow structure and a slightly greater abundance 

of augite, olivine, and apatite. The labradorite phenocrysts are more 

basic, readings on albite-Carlsbad twins indicating a composition near 

Ab3An4 . The widths of the albite lamellae are very variable. The 

augite phenocrysts occur in stout prisms, very pale green in color, generally crystallographically bounded in the prism zone, l/ut rounded on 

the ends. Extinction angles were obtained, of c: £ = 45°. The largest 

augite phenocryst in the slide is less than 2 lnm in length. The olivine is 

in small, sharply idiomorphic crystals, and in larger anhedra from 

0.5 mm to 1 mm in diameter. Apatite is noticeably abundant in rather 

stout, well-formed prisms, both in the augite and in the groundmass. 

This is evidently a somewhat more basic facies than that on the summit of the West Dardanelle.

The most interesting facies (1419 S.N.) of the Dardanelle flow occurs 

3f miles southwest of Clover Meadow, at the point where the latites 

pass under a portion of the andesitic breccias to the west. Megascopically the rock resembles very closely the rocks just described, but the 

groundmass is apparently slightly more crystalline.

Under the microscope it shows the usual pbenocrysts, lying in a 

groundmass that is distinctly more crystalline than the preceding, and 

recalls certain facies of the Table Mountain flow. The plagioclases are 

beautifully twinned according to the albite, together with the Carlsbad, 

and occasionally the pericline, laws. The extinction angles (30° and 

13.5°, 29° and 15°) on albite-Carlsbad twins, cut in a zone perpendicular to the twinning plane, indicate a labradorite somewhat more basic 

than AbnAn4 . Some of the larger crystals have glassy inclusions, as 

in the Table Mountain flow. The specific gravity of these labradorite
48 LAVA FLOWS OF THE SIERRA NEVADA. [BULL.89.

phenocrysts, determined' by suspending a small fragment in Thoulet 

solution, is 2.667, which is rather low for a labradorite of such basicity 

as the extinction angles indicate.

The augite is identical with that already described. Sharply idiomorphic cross sections of the prism zone are frequent, and often show 

twinning on the orthopiuacoid. Extinction angles were measured up 

to c : £ = 44°. Olivine is present only in very subordinate"amount.

The groundmass consists of well-developed lath-shaped microlites of 

plagioclase and small crystals of augite, plivine, and magnetite, lying 

in a gray clondy glass. The great preponderance of the feldspars, both 

in the groundmass and among the phenocrysts, is a striking characteristic of the slide. The lath-shaped feldspars, which are thickly 

crowded together, are generally twinned, and have extinction angles 

corresponding to labradorite. When the section is examined with low 

power and crossed nicols it is very difficult to make out any glass. 

The spaces between the distinctly lath-shaped plagioclases nearly all 

show more or less double refraction, the only parts remaining dark 

being such as are already rendered nearly opaque by thickly crowded 

globulites. By using an immersion objective, and focusing up and 

down iu the section, it appears that the labradorites of the groundmass 

are really tabular parallel with the brachypinacoid, and that these 

faintly doubly refracting portions of the slide are the result of an overlapping of glass and approximately brachypinacoidal sections of labradorite. They generally show the emergence of an acute bisectrix or 

optic axis in convergent light, which, combined with the fact that they 

seldom occupy the full thickness of the thin section, is sufficient to 

account for their low double refraction and rather uncertain extinctions. Naturally they do not show the albite twinning. It was at first 

supposed that they might be orthoclase, or at any rate a different feldspar from the well-defined labradorite laths, but careful focusing 

showed that all gradations could be traced from sections of labradorite 

cut at right angles to the plane of greatest extension, and therefore 

showing sharp albite twinning and usually occupying the full thickness 

of the slide, to those cut at an oblique angle and showing more shadowy 

lamelke and less distinct lath-shaped outline, and finally to sections 

cut at only a very small angle with the brachypinacoid, occupying but 

a fraction of the whole thickness of the section, or thinning out to a 

feather-edge, and consequently showing no twin lamination and low 

double refraction.

The glass in which these well-developed plagioclases lie is in itself 

clear and colorless, but is usually crowded with dark globulites which 

render it nearly opaque with low or moderate powers. By using 

Becke's method the clear glass shows a lower index of refraction than 

the balsam, although the observation is difficult to make on account of 

the abundant globulites. With a No. VII Seibert immersion lens these 

globulites, which appear like black, opaque dust particles with low
KANSOJIE.] DAKDANELLE FLOW. 49

powers, are in part transparent, and composed of a pale greenish substance of high refractive index. Within this substance is frequently a 

smaller black dot which remains opaque and is probably magnetite. 

In their general appearance the globulites with dark central spots 

recall the well-known cells seen in micro-preparations of hyaline cartilage. Not all the globulites, however, are compound. Some are wholly 

transparent, while others are wholly opaque. It is thought that the 

transparent?greenish substance is probably augite.

A portion of this rock was finely powdered and passed through a 

No. 120 sieve. The fine dust was sifted out through a piece of linen 

and the remaining powder washed, dried, and placed in Thoulet solution of about 3.15 sp. gr. A powder at once fell which consisted of 

augite, olivine, and magnetite. Upon dilution to sp. gr. 2.626, about 

half the remaining powder came down. This portion was easily separated by a small horseshoe magnet into two parts, a magnetic black 

powder aud a nonmagnetic white powder. The magnetic portion examined under the microscope was found to consist of fragments of the 

globulitic glass, in which were included microlites of the various minerals of the groundmass, particularly labradorite. The nonmagnetic 

portion consisted of fragments of labradorite free from glass.

Upon dilution of the heavy solution to sp. gr. 2.485, practically all 

the powder fell. This portion also was nearly all magnetic, and the 

magnet left only a small residue of white, nearly pure plagioclase 

powder. The black magnetic portion seen under the microscope 

resembled that just described. No great diiference could be observed 

between the powder which fell at 2.626 and that which came down at 

2.485, except that the nonmagnetic portion was smaller in the latter. 

This lack of distinctive difference was probably due to the unusual 

fineness of the powder and its tendency to float in the fluid. It is 

evident from the experiment, however, that the globulites consist in 

part of magnetite, and that the latter mineral forms an important, 

although not conspicuous, constituent of the rock. The specific gravity 

of the rock as determined by the chemical balance is 2.61. The glass 

in which the globulites lie must, accordingly, be light.

In an attempt to determine the part played by the'considerable percentage of potash shown in the chemical analysis of the rock (Column 

IY, page 58), a few grains of the magnetic and of the nonmagnetic powder were treated with hydrofluosilicic acid. The magnetic powder 

afforded abundant crystals of potassium fluosilicate, as well as of sodium 

and other bases, while the nonmagnetic grains showed only the fluosilicates of sodium, calcium, and aluminium, indicating that the greater 

part of the potash is in the undifferentiated glass, a result that accords 

with its low specific gravity.

The other constituents of the groundmass consist of not very abundant grains and crystals of augite, olivine, and magnetite, some small 

patches of greenish-yellow serpentine, aud an occasional small zircon. 

Bull. 89 4
50 LAVA FLOWS OF THE SIERRA NEVADA. . [BULL. 89.

A rock remarkably similar to the one just described was found in the 

Assos collection already referred to. This (A. E. 240) is a dark, compact rock with splintery fracture, resembling a basalt, and labeled as 

coming from Husseinfagy, Asia Minor. Under the microscope it shows 

pheuocrysts of labradorite and pale-greenish augite. The groundmass 

shows the same structure as the preceding rock, the same well-developed 

plagioclase laths, and a glassy matrix thickly crowded with the same 

dark globulites. The thin section also contains numerous small serpeiitinous p'seudoinorphs, after a mineral that was apparently olivine.

In the absence of a chemical analysis it would be hardly safe to assert 

the practical identity of this rock with the Dardauelle latite; but the 

work of Washington 10on the rocks of Smyrna and Pergamon shows that 

the chemical type of the latites is well represented in thi§ region.

A specimen (1956 S. N.) from the other side of the andesitic ridge, 

about a mile from the preceding, stands megascopically halfway 

between the typical Dardanelle facies and the typical Table Mountain 

facies, showing phenocrysts of labradorite up to 10""'" in length.

Under the microscope the thin section shows the usual labradorite 

and augite crystals, with smaller ones of magnetite. The olivine is very 

inconspicuous and appears to be confined to scattered grains or small 

crystals in the groundmass. The latter, which is rather coarsely 

hyalopilitic, consists of well-developed laths of plagioclase lying .in a 

light-brown glass. These laths, instead of having squarely truncated 

ends, show a great tendency toward skeletal forms, splitting up, and 

projecting long, delicate spines into the glass. Others consist of a thin 

rectangular shell filled with brown glass; This glass, which occupies 

a considerable proportion of the slide between the larger laths, has a 

beautiful frosted appearance, due to its being crowded with still more 

delicate forms of growth than those of the larger laths. All the latter 

are well twinned and show extinction angles corresponding to labradorite. Small prisms of apatite and grains of magnetite, augite, and 

olivine are the other constituents of the grouudmass. The glass, when 

examined with an immersion lens,- is seen to be full of minute globulites, which give it its brown color. Some of the larger of these are 

transparent.

Three-fourths of a mile northward from the locality of the foregoing 

specimen a remnant of the Dardanelle flow, too small to map without 

exaggeration, rests upon a larger and broader mass of the biotite-augitelatite. It is very frothy in places, especially near its base, and the 

specimen (1953 S. N.) taken from the more compact portion shows 

numerous small round vesicles. Megascopically it resembles closely 

some of the Table Mountain latite, the labradorite phenocrysts being a 

little larger and more abundant than in the typical Dardanelle facies. 

The microscope shows large phenocrysts of plagioclase and smaller 

ones of olivine and augite lying in a hyalopilitic groundmass.

i Am. Jour. Sci., 4th series, Vol. Ill, 1897, pp. 41-5Q.
HANSOME.] DARDANELLE FLOW. 51

The plagioclases are twinned with beautiful sharpness, frequently 

combining- both albite and Carlsbad laws. Determinations made on 

such compound twins by the method of Michel Le>y, using- the convenient little apparatus devised by Jaggar 1 to tilt the section into 

the proper positions, indicated a mixture somewhat more basic than 

Ab 3 An 4. These phenocrysts are notable for their frequently very irregular outlines and deep embaymeuts. The bays often exhibit the flow 

structure of the groundmass more conspicuously than other portions, 

streams of parallel plagioclase microlites curving in and out of their 

open mouths, and contrasting with the finer stagnant groundmass 

caught in the deeper ramifications of the bays, arid therefore out of 

reach of magmatic currents.

Next to labradorite, olivine is the most conspicuous phenocryst an 

unusual thing in these latites. It forms well-bounded crystals, in the 

usual stout prismatic forms, sometimes nearly 0.5""" in length. These 

phenocrysts are not very abundant, as only five were seen in an ordinary thin section about 1.5 cm square. The augite is still less abundant, 

and in smaller pheuocrysts than the olivine.

The grouudraass is made up of laths of labradorite, small augites 

and olivines, grains of magnetite, a few prisms of apatite, and brown 

glass. The labradorite microlites show a tendency toward skeletal 

forms resembling those described in the preceding slide.

The last specimen (1886 S. N.) of the Dardauelle flow to be described 

is from the area one-half mile northeast of McKay's, the most westerly 

point at which the lava belonging to this flow has been identified. It 

is here slightly vesicular, with the plagioclase phenocrysts arranged 

with their longer dimensions distinctly parallel. These a,re sometimes 

10 mi" in length, and show albite and Carlsbad twinning. Their size 

and number cause the rock to resemble the typical facies of the Table 

Mountain flow very closely.

Under the microscope it shows large labradorite phenocrysts with the 

usual abundant inclusions, lying in a groundmass that is something 

between hyalopilitic and intersertal. It consists of lath-shaped labradorite microlites, .crystals of augite, olivine, and magnetite*, and an 

occasional apatite, lying in a brown glass like that in the section just 

described. A little serpentine is also present in tbe groundmass, in 

part replacing grains of olivine and in part in irregular patches. No 

pheuocrysts of augite or olivine were seen.

Fragments of labradorite, picked out from the powdered rock under 

the microscope, were found by means of Thoulet solution to have a 

specific gravity of 2.648, which again is low for a normal plagioclase of 

the basicity indicated by optical tests. But it is extremely difficult 

to get fragments that are free from glassy inclusions and at the same 

time large enough to give the best results when suspended in a heavy 

fluid.

1 A simple instrument for inclining a preparation in the microscope: Am. Jonr. Sci., 4th series, Vol. 

Ill, 1897, pp. 129-131.
52 LAVA FLOWS OF THE SIERRA NEVADA. [BULL. 89.

From the foregoing descriptions it can be seen that the typical facies 

of the Dardanelle flow resembles that of the Table Mountain flow very 

closely indeed, while in certain facies they are practically identical. 

The general distinguishing features of the Dardanelle flow are quantitative rather than qualitative. Its phenocrysts are smaller, the ground 

mass is finer; olivine is not quite so abundant, and occurs in smaller 

crystals.

ASSOCIATED VOLCANIC ROCKS.

Olivine basalt, as already mentioned, has been met with only at the 

West Dardanelle, where it forms a thick series of flows, beneath the 

latites, and rests in part upon the granite" and in part upon rhyolite 

tuff. It is a dark, even-grained rock, in which the only megascopic 

phenocrysts are some dark-brown crystals up to 0.5 c:" in length, showing a distinct cleavage, and outlines suggesting pseudomorphs after 

olivine. A little fresh oliviue can also be detected with the lens. This 

rock weathers much more readily than the latites above it, and is otherwise quite different megascopically.

Under the microscope (1007 S. N.) it shows a typical basaltic or intersertal structure, the well-developed plagioclase laths, averaging nearly 

0.5 """ in length, lying in every direction, with the triangular interstices filled with a nearly opaque glassy base and abundant yellow 

pseudomorphs after olivine. The plagioclase is perfectly fresh and 

sharply twinned. Combinations of the albite and Carlsbad laws are 

frequent, and give extinction angles indicating a labradorite rather more 

basic than the mixture Ab3 An.,, probably about Ab2An:; . Olivine 

occurs with the usual characteristic outline, and is the only mineral 

that rises to the rank of a pheuocryst. It is very abundant, but is 

rarely fresh, being usually more or less altered to a bright orange-yellow 

pseudomorphous mineral, which has received the name of iddingsite.1 

The alteration proceeds from without inward, and all stages may be 

observed from olivines which have just begun to be attacked to those 

which have been wholly transformed into yellow pseudomorphs. 

Occasionally there appears to be an intermediate stage, the oliviue 

being bordered by an ordinary greenish serpentine,' and this in turn 

surrounded by the iddingsite. This relationship, however, suggests the 

possibility that the iddingsite may be an early, or even a inagmatic,2 

alteration, whereas the serpentine is the ordinary product of atmospheric weathering. A similar relation was noted in the diabase of Point 

Bonita.3 The iddingsite preserves perfectly the sharp idiomorphic outlines of the olivine. In its cleavage, finely fibrous structure, pleochroisin, and double refraction it agrees with the iddingsite described from 

the much older diabase of Point Bonita, which was regarded as being

1 Lawson, Geology of Carmelo Bay: Univ. of Calif., Dept. Geol., Bull., Vol. 1,1893-96, pp! 31-36. See 

also llansoine, ibid., Vol. I, pp. 90-92; and Smith, Proc. Calif. Aeiad. Sci., 3d series, Geology, Vol. I, 

1897, pp. 38-40.

2 See Washington, Italian petrological studies, II: Jour. Geol., Vol. IV, 1896, pp. 835-836.

3 Loc. cit.
RANSOME.] ANDESITIC TUFF-BRECCIA. 53

probably derived from olivine, although the original mineral had all 

disappeared.

The augite is not abundant, and is rather unevenly distributed in 

the slide. It occurs in irregular areas between the labradorite laths, 

with no crystal form of its own, and has the pale-brown tint characteristic of basaltic augites, as opposed to the greenish augites and diopsides of the andesites. Patches of greenish-yellow serpentine are abundant. They are rounded in outline, and appear to fill small vesicles in 

the glassy base. The latter forms a considerable part of the rock, and 

is rendered nearly or quite opaque by a fine black dust, probably magnetite. The specific gravity of the rock is 2.78. A chemical analysis 

will be found in Column VIII of the table on page 58.

Andesitic breccia or tuff of the ordinary Sierra Nevada type is, as 

already stated, very abundant in this region. It is not, petrographically speaking, a particularly interesting rock, and in spite of its clastic 

origin the larger fragments show a fairly uniform character over the 

whole district. They are usually composed of a hornblende-pyroxeneandesite, in which the large brown hornblende phenocrysts arc in 

various stages of resorption in different specimens, so that this mineral 

is sometimes a conspicuous and abundant porphyrifcic constituent, occasionally showing crystals up to 2.5cm in length, and at other times has 

almost wholly disappeared. The other phenocrysts seen in. thin section 

are labradorite, characterized by zonal structure and undulatory extinctions, pale-green augite, orthorhombic pyroxene, and occasionally 

olivine, all lying in a hyalopilitic groundmass with rather abundant 

glass. Although many specimens and thin sections have been studied 

from different parts of the area, three only, collected from the breccia 

just beneath the latite south of Clover Meadow, will be described in 

full as fair types of the whole.

The first of these (1437 S. E".) is dark gray in color and shows black 

phenocrysts of hornblende up to 5mm in length, and a few small plagioclases, lying in a dark, fine-grained matrix. Under the microscope it 

shows large pheuocrysts of brown hornblende with abundant smaller 

ones of plagioclase, rather less numerous augites, and still less abundant orthorhombic pyroxene. Among the smaller, less conspicuous 

phenocrysts inigh t also be included olivine and magnetite. The groundmass is light brown.in color and hyalopilitic.

The hornblende is the usual brown variety, and the large crystals 

are rounded in outline and surrounded by the opaque resorption rims 

common in andesitic rocks. There is frequently also an outer border 

which, is distinguishable from the groundmass in being clearer and in 

the local abundance of augite and magnetite grains.

The plagioclase phenocrysts give extinctions of albite-Carlsbad twins 

corresponding to labradorite (Ab3An4). They are rather small, but very 

abundant, and are characterized by zonal structure and undulatory 

extinctions, particularly in sections approximately parallel to the
54 - LAVA FLOWS OF THE SIERRA NEVADA. [BULL. 89.

brachypinacoid. In this respect they are well contrasted with the 

sharp regular twinning and definite extinctions of the labradorite of 

the latites.

The augite is pale green to nearly colorless, and gives extinction 

angles of c : £ = about 45°. It is frequently idiomorphic in the prism 

zone, and is in general like the augite of the latites.

The orthorhombic pyroxene occurs generally in smaller and more 

slender prisms than the augite. It is in every way similar to that 

described on page 42 in an andesitic inclusion in the biotite-latite, and, 

as shown by its faint pleochroism and double refraction, is probably 

bronzite rather than enstatite.

The olivine is in small grains and irregular crystals and is quite 

accessory in amount.

The groundmass consists of small microlites of plagioclase, usually 

showing albite twinning, and brown glass. The rock may be called a 

hornblende-augite-bronzite-andesite.

A second specimen (1438 S. IS".) from the same breccia resembles the 

preceding, but is a little darker in color and shows numerous crystals 

of dark olive-green augite 2 or 3 mm in length. The microscope shows 

large phenocrysts of augite and smaller ones of plagioclase and olivine, 

lying in a microlitic glassy base. The large augites are very pale 

yellowish-green in color and nonpleochroic. They sometimes show 

crystallographic outlines, and are sometimes rounded. The angle c : ,c 

was found to be at least 46°.

Brown hornblende in large rounded phenocrysts with black resorption rims also occurs in the rock, but only a single fragment was 

included in the thin section studied.

The plagioclases are prevailingly broad lath-shaped in outline, with 

a central portion full of small glass inclusions. They generally show 

twinning according to the albite law, not infrequently combined with the 

Carlsbad law. The measurements of the extinction angles of these two 

sets of lamellae indicate a labradorite rather more basic than Ab:)An4 .

Olivine is rather abundant, in more or less idiomorphic crystals of 

small size, with occasional larger anhedra, and is quite fresh.

The groundmass is rather glassy, but contains grains of magnetite 

and abundant small microlites. Lath-shaped microlites of feldspar are, 

however, notably lacking, and the groundmass can scarcely be called 

hyalopilitic. Apatite is present in small amount as inclusions in the 

augite. The rock may be called a hornblende-augite-andesite, but the 

abundance of the oliviue indicates a rather close relationship with 

the basalts.

A third specimen (1439 S. N.), much like the preceding, but less 

plainly porphyritic, is dark gray in color and somewhat basaltic in 

appearance. The lens reveals small plagioclases, with augite and olivine, in a fine dark groundmass. Under the microscope it shows the 

same general structure as the preceding rocks. The augite, however,
IANSOME.] , RHYOLITE. ' 55

is in smaller phenocrysts and not quite so abundant, and no hornblende 

appears in the slide. The olivine, on the other hand, is present in 

rather greater amount, often partly serpentinized. The plagioclase is 

labradorite (Ab3An4 ), frequently showing wavy extinctions and zonal 

structure. The inner portions of the crystals are usually the more basic. 

The rock would be classed as an augite-andesite.

Types of andesite other than those described may be found 'among 

the fragments of the breccia in different portions of the region. On the 

ridge just north of Beaver Creek a beautiful light-gray hornblendeandesite (1966 S. N.) was collected, in which the pyroxene present is 

confined to an insignificant amount in the groundmass. The hornblende in this facies is green in transmitted light, with the pleochroism 

a = light greenish yellow, fr = olive green, and & dark yellowish 

green. The absorption is fr = £ > a, and c : c = 16° at least. Another light-gray fragment (1975 S. N.) with conspicuous porphyritic 

hornblendes, taken from the breccia 3J- miles northeast of Pennessy's, 

shows the usual brown hornblende in thin section. The groundmass 

contains abundant small microlites, which appear to be enstatite. A 

thoroughly typical hornbleude-andesite was collected 3 miles south of 

Big Trees in which the hornblende phenocrysts are abundant. Seen in 

thin section, they are surrounded by narrow black rims and show strong 

pleochroism, a = light yellowish green, XT = bright chestnut-brown, 

and jc = deep rich mahogany-brown. The absorption is a < IT < £. 

The groundmass is typically hyalopilitic and contains a little augite. 

Other andesites occur in which the hornblende, if, as seems probable, 

formerly present, has been wholly resorbed, giving pyroxene-andesites 

in which augite and orthorhombic pyroxenes vary in relative proportions. The rarer accessory minerals of the intermediate effusive rocks 

are not well represented in the Sierra Nevada andesites. A small 

crystal of zircon can occasionally be detected, and a single crystal of 

rutile (?) was noted in one thin section.

No chemical analyses have been made of the andesites of this area, 

but they probably do not depart from the ordinary Sierra Nevada type, 

in which total alkalies are generally less than 6 per cent, with soda in 

excess of potash. Some analyses of these andesites have recently been 

published by Turner.1

Massive rJiyolite occurs within the area of the map only at the point 

previously mentioned, just west of the Dardanelles. It is a fresh, 

nearly white rock, showing small phenocrysts of sanidine and a palepink feldspar, with a few grains of quartz, lying in a cryptocrystalline 

groundmass. Under the microscope it shows phenocrysts of sanidine 

with an occasional acid plagioclase and small biotite scales in a nearly 

colorless, homogeneous, microfelsitic groundmass. The sanidine does 

not show good crystal outlines, and is without twinning. It has a lower 

index of refraction than the balsam, a specific gravity as determined

' Seventeenth Aim. Kept.. IT. S. fieol. Survey, Part I, 1896, p. 731.
56 LAVA FLOWS OF THE SIERRA NEVA'DA. [BULL. 89.

by Thoulet solution of 2.542, and yielded abundant octahedra of potassium fluosilicate with hydrofluosilicic acid. The quartz occurs in little 

nests of interlocking grains and not as distinct porphyritic crystals. 

The gronndmass shows a few scattered grains of magnetite and a small 

crystal of zircon.

Rhyolitic tuff is much more abundant than the massive rhyolite 

within the district studied. It is usually white in color, fine grained, 

and somewhat friable, although secondary silicification has frequently 

indurated the exposed surfaces of the beds. The coarser, more crumbling facies generally show fragments of sanidine, microtine, and 

quartz, and sometimes, as on the south side of tbe Dardanelles, waterworn pebbles of foreign material. As mentioned in the preceding 

pages, this tuff sometimes shows columnar structure.

Under the microscope the rhyolite tuff usually shows more or less 

angular fragments of sanidine, plagioclase, and more rarely quartz, 

with scales of biotite, lying in a nearly colorless matrix. The latter is 

almost isotropic, but is generally somewhat chalcedonized. Most of the 

sections show the "aschen-structur" of Miigge 1 in great perfection, and 

all intermediate facies occur between those made up of the fresh cresceutic glass spicules of a finely comminuted volcanic ash 2 (1823 S. N.) 

and those in which secondary silicification has in great part replaced 

the intricate reentrant curves of the glass shards by finely radial, concentric bands of chalcedony, polarizing feebly between crossed nicols, 

and giving rise to a kind of secondary axiolitic structure common in 

older rhyolitic tuffs and concerning whose origin there has been some 

debate (1973 S. N.).

Various tuffs occur within the area embraced by the map which differ 

somewhat from the ordinary gray andesitic tuffs of the region. They 

are generally finer, softer, and lighter in color than the latter and are 

found only in a few small patches. Microscopic investigation shows 

that they are either andesitic or latitic in character, the distinction 

between the two being not readily made in their tuffaceous forms.

A mile and a half south of Fennessy's a thin stratum of porous, lightgray tuff (1978 S. N.) rests upon the biotite-augite-latite and separates 

it from the overlying andesitic breccia. Megascopically this shows 

abundant small fragments of white pumice inclosed in a finely comminuted volcanic paste. Under the microscope it exhibits numerous 

areas of nearly colorless pumiceous glass, together with crystals of 

labradorite, augite, brown and green hornblende, biotite, and apatite. 

The biotite occurs both as isolated crystals and inclosed in the puiniceous glass. There are also abundant fragments showing microlitic 

glassy base, some of which appear to be andesite, while others resemble the fine groundrnass of some of the massive latites. The apatite 

is in small prisms, and the slide also contains a little magnetite and 

epidote. The presence of biotite, which was not found in the andes-

'Neues Jahrbuch fur Min., etc., Beilage-Band 8, p. 648. See also G. 0. Smith, Geology of tbe .Fox 

Islands, Maine, Skowliejrnn, 1800, p. 30. 

2 Diller, Science, Vol. IV, 1884, pp. 651-054.
RANSOME.] CHEMICAL COMPOSITION. 57

ites of the region, and the absence of orthorhombic pyroxene, suggest 

that this tuff may belong to the latitic series.

Just south of Mill Creek, near its mouth, the augite-latite, capping 

the small hill previously described, is underlain by three beds of soft 

tuff. The lowest of these is light yellow, friable tuff, containing fragments of fine white pumice and small rolled pebbles. Under the microscope it is seen to be made up of glass shards showing typical ash 

structure, with fragments of pumice and a few grains of clastic quartz, 

the whole being somewhat chalcedonized.

The bed just above this is a fine, white volcanic sand that was not 

microscopically examined, while the topmost bed is apparently an ordinary audesitic tuff, albeit somewhat finer than is common in this region.

CHEMICAL COMPOSITION OF THE SIERRA NEVADA

TJATITES.

In the accompanying table (p. 58) the chemical analyses of the latites 

form all three flows are brought together for comparison. In spite of a 

certain range iu the silica percentages, they are all closely related 

members of a series. They are not far from the andesites in general 

composition, but are slightly higher in silica and distinctly so in alkalies, 

the potash being always slightly in excess of the soda.1 Compared 

with typical trachytes, these rocks are higher in lime and magnesia and 

lower in silica and alkalies, while the preponderance of potash over 

sodti is usually much more marked in the trachytes.

As would be expected from the microscopical study of the thin sections, the rock of the Table Mountain flow is somewhat more basic than 

the biotite-augite-latite, while the Dardanelle facies occupies an intermediate position. The Shaws Flat rock (Column I) shows the greatest 

basicity; the greater amount of lime and magnesia, as compared with 

the other analyses, being in harmony with the slightly greater abundance of olivine and augite as observed in the thin section. Titanic 

oxide is present iu all the analyses,°and usually in noticeable amount, 

indicating that the magnetite of the rocks is probably titahiferous. 

Analysis VI is exceptional iu containing a small amount of carbon, 

which is doubtless due to some organic matter included in the lava.

The most noteworthy feature of the analyses, however, taken in connection with the mineralogical composition of the rocks, is the amount 

of potash shown. As already stated, by far the greater number of the 

thin sections (excepting, of course, the biotitic facies, which, however,

'It is important to note that this statement applies only to the percentage ligures in the analyses. 

When the molecular proportions of soda and potash are compared it becomes apparent that, as far as 

the actual mineral-forming efficiency of these alkalies is concerned, it would be more accurate-to say 

that they are very nearly equal; for the soda molecule may sometimes be present in slightly greater 

amount than the potash molecule, although the preponderance, when reckoned in percentages, is in 

the other direction. But as rock analyses are not yet, as a general thing, niolecularly expressed and 

compared, the common mode of percentage comparison has been retained in the characterization of 

the latites. The petrographer accustomed to translate his chemical analyses into molecular proportions will not, when reading the following pn?:es, lose sight of the suggestion embodied in this note.
58 LAVA FLOWS OF THE SIERRA NEVADA. [BULL, i

are no richer in potash than the others) contain no characteristically 

potash-bearing mineral. Several of the analyses contain as much as 5 

per cent of potash, which, if it were present in the form of orthoclase,' 

would make up nearly 30 per cent of the rock:. This amount is entirely 

too large to be accounted for by the assumption that it is present in the 

form of orthoclase microlites which have escaped detection among the 

plagioclases of the groundmass. It is fairly certain that nearly all of 

the potash in those facies which do not contain biotite is present in the 

residual glass of the groundmass. This conclusion harmonizes with 

the results of the micro-chemical tests described on page 49, and with 

the previously noted low specific gravity of the glass.

Frequently 1 in rocks of intermediate composition, like the latites, 

the orthoclase forms a thin envelope around the basic plagioclases, 

while in the plutonic monzonites the orthoclase was the last mineral 

to crystallize, forming a mesostasis for the earlier minerals. In the 

Sierra Nevada latites the conditions under which orthoclase (or some 

other potash-alumina silicate) would separate out were never reached. 

This indicates that the method sometimes employed of assuming the 

presence of orthoclase in the groundmass of an effusive rock from the 

character of the bulk analysis is one that requires caution in its use.

Table of chemical analyses of Sierra Nevada latites and associated volcanic rocks.

Si02 .............

Tin

ALA,.. ..........

Fej03 ... .........

FeO .............

MnO. ............

MgO. ............

CaO. ..............

BaO .............

Na./) ............

KS 0 .............

T> r>

H2 0 below 110° . .

Total......

Sp.gr......

I.

56.19

.936 

.69

16.76

.162 

3.05

.019 

4.18

.058 

.10

3 79

.094 

6.53

.116 

.19

2.53

.040 

4.40

.047

.66

.34

SrO, tr. 

Li2 0, tr.

1UO. 02

II.

59.88

.998

5.09

.090

3.90

.062 

5.06

.053

III.

56.78

.946 

1.15

16.86

.163 

3.56

.022 

2.93

.040

 3.41

.085 

6.57

.117

3.19

.051 

3.48

.036 

.42

1.21

.15

CO,. 18

99.89

2.67

IV.

59. 43

.990 

1.38

16.68

.161 

2.54

.015 

3.48

.048

1.84

«.046 

 4.09

.073 

.14

3.72

.059 

5.04

.053 

.58

.72

.27

Zr02 . 08 

SrO, tr.

Cl .05

100. 04

2.61

V.

61.09

1.018

4.94

.088

3.69

.059 

5.27

.055

VI.

62.33

1.039 

1.05

17.35

.168 

2.98

.018 

1.63

.022 

.08

1.05

.026 

3.23

.057 

.24

4.21

.067 

4.46

.047 

.29

. .75

.44

SrO .05 

Li2 0, tr. 

FeS2 . 08 

C .11

100. 33

VII.

65.81

1. 096 

.54

15.11

.146 

1.85

.011

.019

.37.

.009 

1.98

.035 

.10

2.59

.041 

5.24

.055 

.23

9 3B

Yin.

48.76

1.26

16.60

5.60

5.01

6.93

8.79

2.47

.66

.19

2.19

1.49

C02 .42

100. 37

2

7Q

IS.

67.57

5.57

4.33

2

00

'See Washington, Jour. Geol., Vol. IV, 1806, p. 551, for several references.
IIANSOME.] CLASSIFICATION OF LATITES. 59

I. Augite-latite (36 S. If.), Table Mountain flow, Tuolumne Table Mountain, near Shnws Flat. 

Tnraer, Kocks of the Sierra Nevada, Fourteenth Ann. Kept. TJ. S. Geol. Survey, p. 491. Hillebrand, 

analyst.

IT. Augite-latite (86 Tuol.), Table Mountain flow, 3 miles southeasterly from Big Trees. Turner, 

Geology of the Sierra Nevada, Seventeenth Ann. Kept. TJ. S. Geol. Survey, p. 727. Fireman,analyst.

III. Augite-latite (1422 S. N.), Table Mountain flow, spheroidal facios, about ]J miles east of 

Clover Meadow. Steiger, analyst.

IV. Augite-latite (1419 S. N.), Dardanelle flow, 4 miles southwest of Clover Meadow. Stokes, 

imalyst.

V. Biotite-augite-latite (85 Tnol.), 3 miles southeasterly from Big Trees. Turner, Geology of the 

Sierra Nevada, Seventeenth Ann. Kept. TJ. S. Geol. Survey, p. 727. Fireman, analyst.

VI. Biotlte-augite-latite (1420 S. N.), 4 miles southwest of Clover Meadow. Turner, loc. cit. Hillebrand, analyst.

VII. Vitrophyrielatite (?) (1866 S.N.), just south of Mill Creek. Analysis partial. Steiger, analyst.

VIII. Olivine-basalt (1007 S. N.), west peak of the Dardanelles.

I.. "Red lava" (1867 S. N.), just south of Mill Creek. Eausome, analyst.

CLASSIFICATION OF THE LATITES.

With the great advance in methods of petrographical research during recent years there has come inevitably greater difficulty and 

complexity in the proper classification of the rocks themselves. The 

greatly increased accuracy of chemical analyses, particularly as regards 

amounts, of the alkalies and minor constituents, and their more 

critical interpretation, together with the strides made in the optical 

investigations of the feldspars by Becke, Federow, Michel L6vy, and 

others, is leading to the gradual splitting up of some of the older and 

more comprehensive groups. A notable example of this tendency was 

Brogger's differentiation of the monzonite family from the syenites, 

while a similar process has been long reducing the once large family of 

the trachytes to a size more commensurate with the minor importance 

of their plutonic equivalents. With the establishment of new families 

there has come into the literature an enormous number of new names. 

In many cases these names are local, being based on mineralogical 

combinations and distinctions that may not be repeated in another 

region or be given the same value by other observers. The common 

custom of providing such facies with a name derived from the locality 

in which they occur is a useful one, but the local, and to a certain 

extent provisional, nature of such names should be borne in mind, and 

they should not be allowed to bury under their accumulating mass 

broader and more rational schemes of classification.

On the other hand, it is no part of pure petrographical science to aim 

directly at ease and simplicity in classification, however anxiously such 

an end may be desired by the general geologist. Petrography in its 

present stage is occupied rightly with critical distinctions. It is only 

by the recognition of such slight points of difference that they can 

ever be transcended and assigned their true value in a really rational 

scheme of rock classification.

Eecognizing the fact that igneous rocks are, chemically, mixtures of 

practically infinite variability within certain limits, the refining tendency of modern methods makes more and more for precision of
60 LAVA FLOWS OF THE SIERRA NEVADA. [BULL.89.

definition and consequent subdivision of the older groups. This gain 

in exactness by no means makes easier the classification of a given 

rock, for it is evident that the greater the number of families the more 

numerous will be the intermediate or transition rocks, since sharp 

lines of demarcation apparently nowhere prevail between closely related 

types. It is a question, of course, how far for purposes of practical 

description such subdivision of larger groups should go, but it is a 

question that may very well be answered by the facts of geological 

occurrence. If a magma of a certain intermediate type with reference 

to two or more well-established families is found to possess geological 

unity, and particularly if it is found to be represented by both plutonic 

and effusive forms, there can be little doubt of the advisability of giving it a distinctive name. Brogger's monzonite magma is an example 

of such a case, and he has shown very conclusively that the plutonic 

monzonites, being orthoclase-plagioclase rocks, should be separated 

from the orthoclase rocks, or granites and syenites, on the one hand and 

from the plagioclase rocks, or diorites and gabbros, on the other, the 

mineralogical distinction being the visible sign of difference in chemical 

composition. In his tabular classification ! he has indicated the effusive 

equivalent of monzonite as tracliyt-andesit, and it is here that the latites 

of the present paper belong, as will now be more fully shown.

It is plain from the descriptions of the latites in the preceding pages 

that, in spite of their superficial basaltic character, they are in no 

sense basalts, being far too high in silica and alkalies and too low in 

magnesia and lime, and differing from the latter rock in microscopical 

structure and in the proportion of the ferromagnesian constituents to 

the feldspars. Their specific gravity, too, is lower than that of basalts 

of equally compact texture.

Their relation to the andesites is much closer, and were it advisable 

to crowd them into one of the well-established older groups they would 

be placed with little hesitation in this family. Leaving out of consideration the glassy base, the particular latites here described possess 

practically the mineralogical composition of audesites. But they differ 

from normal andesites in chemical composition, being generally slightly 

lower in lime and magnesia and always higher in alkalies. In the 

andesites the total alkalies are as a general rule less than 6 per cent, 

with soda in excess of potash. In the latites the total alkalies range 

from 6 to 10 per cent, with the potash equal to or slightly in excess of 

the soda.

Eocks of this type can hardly be classed as trachytes if the latter 

name is to retain any precision of meaning. jSTot only are they decidedly untrachytic in color and texture, but they differ widely mineralogically from typical trachytes. Sanidine, instead of being the dominant feldspar, is entirely absent and the conspicuous feldspar is here

1 Die Eruptivgesteiue des Kristianiagebietes; II. Die Emptionsfolge dor triadischeii Eruptivgesteine bei Predazzo iii Siidtyrol. Kristiania, 1895, p. 60.
RANSOMK.] CLASSIFICATION OF LATITES. 61

labradorite. As already noted, Turner J has provisionally classed some 

of the latites with the trachytes on the basis of their chemical composition. The analysis upon which he bases his comparison is quoted 

from Zirkel's Lehrbuch der Petrographie,2 and, as Turner remarks, 

"contains more lime and less silica than most of the analyses given by 

Zirkel." The analysis in question is one by Eicciardi 3 of the so-called 

"trachyte" of Bolsena, and is quoted in Column YI of the table of 

chemical analyses on page 66. Concerning this " trachyte" Washington writes:

Voin Katli first called attention to the abnormal chemical character of the 

"trachyte" of Bolsena, though he speaks of it as containing no plagioclasc, probably owing to the rarity of the multitude twinning. As will be seen from Klein's 

descriptions and my own, and from the analyses, the peculiar "trachytes" of the 

region are remarkable; mineralogically for their richness inplagioclase and the frequent occurrence of olivine as an essential constituent, and chemically for their low 

silica and high lime and magnesia. Therefore they are not trachytes proper, but 

correspond to the trachy-dolerites of Abich and Hartung, and to some of the 

andesitic trachytes of Rosenbnsch, and we shall see that, they may be regarded as 

effusive representatives of Brogger's abyssal monzonites. These olivine-free effusive 

rocks will be called by the name of Vulsiniie, from the Etruscan tribe Vulsinii, 

formerly inhabiting this region.4

There is thus fresh confirmation of the result already stated, that 

the latites of the present paper belong neither with the normal 

trachytes nor yet with the normal andesites, but occupy a position 

chemically about midway between the two.

Effusive rocks with a chemical composition corresponding to this intermediate taxonomic position appear to be not uncommon, and on page 

66 the chemical analyses of a number of such rocks are placed together 

in tabular form for comparison. Nos. I to XIX inclusive are analyses 

of latites (which in the table are given the names assigned them by the 

authors quoted), while No. XX is the mean of the 19 analyses which 

precede it. JSTos. XXI and XXII in the second division of the table 

are a typical andesite and a typical trachyte respectively, being 

inserted to show thedntermediate character of the latites. The latter 

as a whole form a fairly uniform chemical series, of which the mean 

agrees closely with the analysis in Column IX.

But when attention is directed to the names and descriptions of the 

various effusive rocks embraced in the table they are found to be 

remarkable more for variety than for uniformity. Thus, besides the 

latites described in thf> present paper, there occur such names as ciminite, biotite-vulsinite. divine-bearing andesitic trachyte, biotite-dacite, and 

sanidine-bearing anaesite. .At first glance such an abundance of names 

for effusive rocks of a single chemical type seems to indicate little else

 Further contributions to the geslogy of the Sierra Nevada: Seventeenth Ann. Kept. TJ. S. Geol. 

Survey, Part I, 1896, p. 729.

'Vol. II, 1893, p. 378.

8Klein, Petrograptiische TJntersuchung einer Suite von Gesteinen aus der Umgebung des Bolsoner 

Sees: Neues Jahrbuch ftir Min., etc., B. B. VI, 1889, p. 8.

4 Italiau petrological sketches: Jour. Geol., Vol. IV, 1896, p. 547.
62 LAVA FLOWS OF THE SIERRA NEVADA. . [BULL.89.

than a state of hopeless confusion in rock nomenclature. But while a 

certain amount of confusion does undoubtedly exist, the multiplicity 

of names has its chief explanation suggested in two other facts partly, 

as pointed out by Iddings, 1 that rock series as they occur in nature may 

traverse existing schemes of classification at practically any angle, but 

mainly, in this case, that the name of a rock is generally determined 

more by its mineralogical than by its chemical composition.

In the case of most igneous rocks, and of nearly all plutonic rocks, 

the principal mineralogical constituents can be deduced with a fair 

degree of certainty from an accurate bulk analysis, and, vice versa, 

from a microscopical examination of a thin section the chemical constitution can be predicted with sufficient accuracy to leave little doubt of 

the general position of the rock in any ordinary scheme of classification. 

But with the effusive latites this appears to be true only in a slight 

degree. In effusive rocks of intermediate chemical composition the 

circumstances which determine the crystallization of the different pos-. 

sible mineralogical combinations appear to depend upon a very delicate 

adjustment of physical and chemical conditions. This is already noticeable in the andesites, where a given magma cooling under certain conditions may give i ise to a hornblende- or bibtite-andesite, and under 

other conditions, by the magmatic resorption" of these two minerals, 

may solidify as a pyroxene-andesite. The latites, being intermediate 

rocks par excellence, and containing more or less unindividualixed 

glass in reserve, exhibit this apparent capriciousness of crystallization 

in an unusual degree.

Thus the vulsinites of Washington " are characterized mineralogically 

by the presence of alkali feldspar with a large amount of basic plagioclase (labradorite to anorthite), together with augite and diopside. 

Hornblende and biotite are not abundant in the type specimens, though 

they may be present in large amounts in other varieties. ... . 

Olivine is wanting, or if present is so in only accessory amounts." 2 It 

should be stated that the facies which Washington regards as his most 

typical vulsinite contains over 9 per cent of potash, and accordingly 

approaches somewhat nearer to the trachytes than do the typical 

latites of the Sierra Nevada.

The biotite-vulsinite from Monte Santa Croce (Column II) is particularly interesting with reference to the point under discussion, and the 

dilomma in which one is placed in attempting to adhere to a purely 

miueralogical classification of these rocks is well expressed in Washington's own words. He says:

We have then a rock which is chemically a ciminite and mineralogically a biotitevulsinite. In regard to the name by which they should be called there may be some 

doubt. From a mineralogical standpoint they are obviously not cimmite, nor 

chemically can they strictly be called vulsinite. Since, however, in the schemes of 

classification in general use at the .present time, the mineralogical composition takes

1 Jour. Geol., Vol. Ill, 1895, pp. 955-956.

2 Jour. Geol., Vol. IV, 189G,p.553.
RANSOMK.] CLASSIFICATION OF LATITES. 63

precedence over the chemical, and bearing in mind the uuadvisability of adding 

new names to the already overburdened nomenclature, I shall designate these rocks 

as b iotite-vulsinite.'

The ciminites are " characterized mineralogically by the presence of 

orthoclase, with basic plagioclase, augite or diopside, or olivine." 2

The anclesite from Carbezo Felipe contains phenocrysts of feldspar 

and b iotite. Sanidine occurs in crystals over a centimeter in length, 

but the main bulk of the feldspar is labradorite, or a plagioclase between 

labradorite and andesine. Both monoclinic and orthorhombicpyroxenes 

are present, and the rock is rich in zircon and apatite. Concerning the 

classificatory position of this rock Osann writes:

The proportion of the alkalies shows that the rock stands close to the group of 

andesitic trachytes a position which is indicated also by the presence of the large 

sanidine phenocrysts. The content in lime and potash, contrasted with the small 

amount of soda, is explained by the fact that basic plagioclase (labradorite) occurs 

as phenocrysts with the sanidine. If the analysis is compared with the analyses of 

other andesitic trachytes, in part olivine-beariug (Mte. Amiata. the Arso flow, Mte. 

Alfina), it is seen to be higher in magnesia. (The Arso rock, in spite of the presence 

of olivine, haa only 1.77 per cent.) This is explained only by the abundance of both 

biotite and orfchorhombic pyroxene/'

The augite-andesite from Mount Pagos is "composed of plagioclase, 

diopside, and biotite, with accessory magnetite, apatite, and zircon, 

lying in a glass base." 4 The plagioclases are labradorite (Abi Aiii), 

but there are possibly a few orthoclase microlites in the groundraass.

The Gleicheuberg trachyte contains, according to Hussak,5 large 

sanidine phenocrysts, fewer and smaller ones of oligoclase (with extinction angles of 12°-15°), biotite, and dark augite, in a globulitic 

base.

The angite-andesite from Kara Tash has numerous phenocrysts of 

labradorite (a little more basic than Abi An,), pale-green diopsides, 

some.biotite, and grains of magnetite, in an abundant, trichitic, glassy 

base.6'

The biotite-dacite from Pergarnon 7 contains phenocrysts of labradorite, with fewer sanidines, biotite, and olive-green hornblende. The 

rock is called a dacite on the basis of its chemical composition, although 

containing no free quartz, thus again illustrating the difficulties 

attendant upon a consistent inineralogical classification of these intermediate rocks.

The sanidine-bearing audesite of the Bosita Hills is described by 

Cross" as containing plagioclase, orthoclase, quartz, biotite, augite, and

'Jour. Gcol.,-Vol. V, 1897, pp. 250-251..

2 Ibid., Vol. IV, 1896, p. 838.

'Beitrago KUT Kenntniss der Eruptivgesteine des Cabo de Gata, II: Zeitsclir. Deutscli. geol. Gesoll., 

vol. 43,1891, p. 720.

4 Washington, On 8ome igneous rocks from Smyrna and Pergauioii: Am. Jour. Sui., 4tli series.- 

Vol. in, 1897, p. 44.

sZirkel, Lehrbuch der Petrographie, Vol. IE, p. 383.

""Washington, loc. oit., p. 44.

' Washington, loc. cit., p. 48.

Troo. Colorado Sci. Soc., 1887, p. 248. -» ~
64 LAVA FLOWS OF THE SIERRA NEVADA. [BULL. 89.

accessory minerals. This rock is said to have its chief development in 

dikes, although occurring also in effusive masses.

The foregoing citations are sufficient to show how great mineralogical 

variety may be presented by rocks having the peculiar intermediate 

chemical composition of the latites. It is possible, and perhaps desirable, to assign the more conspicuous and well-marked of these mineralogical combinations separate names, but the number of the latter is 

apt to be large, and they are of a distinctly lower grade of importance 

than those rock names which express not only a certain mineral constitution but a corresponding and characteristic chemical composition 

as well.

It accordingly seems advisable to attempt to bring into common use 

some more general name to embrace all theeffusive rocks stand ing chemically about midway between the typical trachytes and the typical andesites a name that can be used as the effusive equivalent of the increasingly 

important plutonic group of the monzonites. I should gladly have 

avoided the necessity of introducing a new name into a rapidly growing 

nomenclature; the more so, as Washington, by his admirablepetrographical studies in the Italian volcanic regions, has added so greatly to an 

accurate knowledge of intermediate rock types which must be necessarily embraced by such a new term. But the Sierra Nevada lavas 

can not be classed with the typical toscanites, vulsinites, or ciminites, 

as denned by Washington, although, like the vulsinites and some of 

the cimiuites, they are to be regarded as the effusive equivalents of the 

monzonites. There is thus a demand for some more comprehensive 

name to cover the mineralogically diverse forms which the monzonitic 

magmas, cooling under effusive conditions, may assume. For this 

reason, and in recognition of the importance and interest of the Italian 

types described by Washington, the name latite, derived from the 

Italian province of Latium, is proposed as a broader term, comparable

in its scope with monzonite, to designate the effusive forms of the 

monzonite magma. Thus it will be seen that certain of the characteristic features of the Sierra Nevada latites, such as the absence of sanidine, the predominance of labradorite, and the presence of a residual 

alkali-rich glass base, are not regarded as essential in the definition of 

the general group of the latites as a whole. The latites described in 

the present paper are merely members of this group, possessing individual characters which would entitle them to names of the same order 

of importance as the vulsinites, toscanites, etc., of Washington. For 

the present, however, no such names are proposed.

Abich and Hartung have used tracliy-dolerite for rocks which in part 

belong with the latites; Fouqu6 and Michel Le"vy, tracliy-andesites; 

Zirkel andEosenbusch, andesitic trachyte; and Brogger tracliyte-andesite. 

But all these compounds are open to objection when a name is required 

for an important group standing midway between the trachytes and 

the andesites. Such a name should consist of a single word, and
RANSOJIE.] CLASSIFICATION OF LATITES. 65

should be free from the undesirable connotations adherent to compounds which have been variously employed.

Keferring again to the table of chemical analyses ou page 67, it will 

be seen that in Columns XXIII and XXIY are placed the analyses of 

two qnartz-bauakites, chosen as being the nearest known dike equivalents of the latites 1 . The correspondence, however, is not quite perfect, as the two analyses show a slight deficiency in lime and a small 

excess of alkalies as compared with the mean of the latite analyses. 

Iddings 2 states that the rocks of these two analyses belong to the banakite series "both niiueralogically and chemically, but are somewhat 

more siliceous, having 5 to 9 per cent more silica. They might properly be given specific names, but at present we prefer to class them 

with banakite. under the name of quartz-banakite, the amount of 

quartz, however, being very small."

The banakites are intermediate rocks in the same sense that the 

latites are. Chemically they possess a rather close analogy with the 

latter rocks, although somewhat lower in silica, and thus tending 

through leucitic facies toward the truly alkaline groups of igneous 

rocks. It is interesting to note that Iddings :! remarks in this series 

the tendency to'ward mineralogical diversity with nearly identical chemical composition, already emphasized in the case of the latites.

In the succeeding columns of the table are placed the analyses of 

several monzonites, quoted from Brogger, in order to show the close 

relationship between these plutonic rocks and the effusive latites. 

Washington has already pointed out this correspondence in the case 

of his vulsinites and cimmites.4 and notes as well analogies with the 

absarokite-banakite series of Iddings.5

1 After the foregoing was in type my attention was drawn to the dike rock descrihcd by Hibsch as 

occurring iu the Bohemian Mittelgebirgo, -which he has named gauteite. (Erlautemng zur geologischen Karte des biihmischen Mittelgebirges: Tschermaks min. u. pet. Mitth., vol. 17,1897, pp. 84-87.) 

This rock also IB perhaps a dike equivalent of the monzonites and latites, although the chemical 

analysis shows rather high alkalies.

2 Absarokite-shoshonite-banakite series: Jour. Geol., Vol. Ill, 1895, pp. 949-950.

3 Loc. cit., p. 951.

* Jour. Geol., Vol. IV, 1896, p. 832.

B Ibid., loc. cit., p. 838. Since the foregoing was written Washington's final paper 011 the Italian volcanic regions has appeared (loc. cit., Vol. V, 1897, pp. 349-377), in which he divides the rocks between 

the trachytes and the andesites into two series the trachyandesites and the tracliydolerites, using 

the former term in a more restricted sense than in his earlier papers, and without the previously 

employed hyphen. The Sierra Nevada latites would fall most nearly within his trachydolerite series, 

although not the strict equivalents of any of its individual members. AVhether some such single 

term as that here proposed shall be used to designate the rocks midway between the trachytes and 

andesites, or whether it-will be found practicable, to divide them into two series as Washington has 

done, may, as the latter suggests in a slightly different connection, be left to the -winnowing action of 

time and usage.

Bull. 89 5
Comparative table of chemical analys

Si02 ...............

T \i~\

A1203 --. ...........

Fe203 - .............

FeO ...............

MnO...... .........

MgO...... .........

CoO

BaO ...............

Na2O ..............

K2O ...............

T> f\

CO2 ... .............

Ig...... ...........

Total ........

I.

55. 4i

18.60

2.09

4.48

4.75

6.75

1.79

6.63

} .25

100. 75

2.70

II.

55.69

19.08

4.07

3.26

3.41

6.87

2.89

4.41

.17

99.85

III.

56.19

.69

1C. 76

3.05

4.18

.10

6.53

.19

2.53

4.46

55

, .66

\ .34

SrO, t. 

Li2O,t.

100. 02

IV.

56.76

2.07

6.95

1.63

6.01

2.43

4.67

.47

^.44

100. 22

2.47

V.

56.78

1.15

3.56

2.93

3.41

6.57

3.19

3.48

.42

.18

.15

99.89

2.67

VI.

57.97

17.65

.63

7.50

.09

1.71

5.53

1.50

5.31

.42

1.82

100.13

2.451

' VII.

58.67

15.07

8.35

2.97

8.07

3.36

3.50

j. .82

100.81

2.765

VIII.

59.41

.01

17.92

1.71

2.40

2.99

4.65

2.63

5.60

.87

1.30

99.49

IX.

59.43

1.38

2.51

3.48

1.84

4.09

.14

3.72

5.04

KQ

, T)

t .27

ZrO2 . 08 

SrO, tr. 

Cl .05

100. 04

X.

59.88

5.09

3.90

5.06

(......

XI.

60.03

1.83

4.15

.09

1.12

6.58

2.31

5.12

.42

P 1.42

100. 12

2.543
SiO*... ............

TiO2 . ..............

A 1 A

Fe/)3 . .............

FeO ...............

MnO. ..............

MgO...... .........

CaO ...............

BaO ...............

NajO ..............

K.O ................

 p r\

H,O ...............

Total........

XXI.

58.47

.51

18.80

3. .-14

2.64

.13

2. 09

6.60

3.58

2.01

.22

, >.92

I M4 

SrO . 0» 

Li2O, tr.

100. J 9

XXII.

60.97

20.92

} 3.81

.29

.14

5.03

8.88

} .83

100. 42

XXIII.

57.29

.72

18.45

( 4.38

I 1.20

2.08

3.57

4.43

5.43

.46

2.18

NiO . 12

100. 31

XXI 7.

60.89

.49

17.14

3.32

.95

.09

1.16

3.58

5.71

.27

1.61

NiO . 19

99.94

XXV.

52.16

22.11

} 8. 58

2.64

8.61

3.35

.80

100. 25

XXVI.

52. 53

19.48

11.07

6.61

2.71

3 17

2.34

99.44

XXVII.

52.81

.71

15.66

X 4.76

4.99

7.57

9 1

..75

i '.93

I 2 .16 

SrO .09 

Li2O, tr. 

Cl .07 

Fl, tr. 

SO3, tr.

100. 24

.02

100. 22

XXVI

54.

.

15. 

3.

5.

3.

8.

3.

4.

.

] .

100.

1 Above 110°. 
68 LAVA FLOWS OF THE SIERRA NEVADA. [BULL. 89.

I. Ciminite, Foutana Fiescole, Viterbo, Italy. Jour. Geol., Vol. IV, p. 849. "Washington, analyst.

II. Biotite-vulsinite, Monte Santa Croce, Kocca Monfiuo region, Italy. Jour. Geol., Vol. V, p, 252. 

"Washington, analyst.

III. Augite-latite (30 S. N.), Table Mountain, near Shaws Flat, Tuolurune County, Gal. Hillebrand, 

analyst.

IV. Olivine-bearing andesitio trachyte, Sassara, Italy. Klein, Neues Jahrbuch fur Min., etc., 

B. B. VI, p. 7. Eicciardi, analyst.

V. Augite-latite (1422 S. N.), Table Mountain flow, 1£ miles east of Clover Meadow, Tuolumne 

County, Cal. Steiger, analyst.

VI. Trachyte (Klein) or vulsiuite ("Washington), Bolsena, Italy. Klein, Neues Jahrbuch fur Min., 

etc.,B. B. VI, p. 8. Kicciardi, analyst.

VII. Ciminite, Monte Cimino, Italy. Jour. Geol., Vol. IV, p. 849. Vom Eath, analyst.

VIII. Andesite, Cabezo Felipe, Cabo de Gata, Spain. Zeitschr. Deutscb.geol. Gesell., vol.43, 1891, 

p. 719. Osann, analyst.

IX. Augite-latite (1419 S. N.), 4 miles southwest of Clover Meadow, Tuolumue County, Cal. Stokes, 

analyst.

X. Augite-latite (86 S. N\), Tuolumne County, Cal., 3 miles southeasterly from Big Trees. Turner, 

Seventeenth Ann. Kept. U. S. Geol. Survey, p. 729. Fireman, analyst.

XI. Trachyte (Klein) or vulsinite ("Washington), San Magno, Italy. Klein, Neues Jahrbuch fiir 

Min., etc., B. B. VI, p. 10. Kicciardi, analyst.

XII. Augite-andesite, Mount Pagos, near Smyrna, Asia Minor. "Washington, Am. Jour. Sci., 4th 

series, Vol. Ill, p. 43. Washington, analyst.

XIII. Biotite-augite-latite (85 S. N.), Tuolumne County, Cal., 3 miles southeasterly from. Big Trees. 

Turner, Seventeenth Ann. Kept. U. S. Geol. Survey, p. 729. Fireman, analyst.

XIV. Trachyte, Gleichenberg, near Steiermark. Tschermaks mineral. Mittheil., 1887, p. 277. 

Smita, analyst.

XV. Augite-andesite, Kara Tash, near Smyrna, Asia Minor. "Washington, Am. Jour. Sci., 4th series, 

Vol. Ill, p. 45. Washington, analyst.

XVI. Biotite-augite-latite (1420 S. N.), 4 miles southwest of Clover Meadow, Tuolumne County, Cal. 

Hillebrand, analyst.

XVII. Biotite-dacite, Pergamon, Asia Minor. Washington, Am. Jour. Sci., 4th series, Vol. Ill, p. 49. 

Washington, analyst.

XVIII. Sanidine-bearingandesite, EositaHills, Colo. Cross, Proc. Colo. Sci. Soc., 1887, p. 250. Eakiiis, 

analyst.

XIX. Vitrophyric latite (?) (1866 S. N.), just south of Mill Creek, Tuolumue County, Cal. Partial 

analysis. Steiger, analyst.

XX. Mean of the important constituents of the 19 preceding analyses.

XXI. Hornblende-pyroxene-andesite (72 S. N.). Downieville area, Sierra Nevada, Cal. Turner, 

Seventeenth Ann. Eept. TJ. S. Geol. Survey, p. 731. Hillebrand, analyst.

XXII. Trachyte (domite), Puy de Dome, Auvergne. Zirkel, Lehrbuch der Petrographie, II, p. 378. 

Lewinsteiu, analyst.

XXIII. Quartz-banakite, dike, near head of Stinkingwater Eiver, Yellowstone Park region. 

Iddings, Jour. Geol., Vol. Ill, p. 947. Melville, analyst.

XXIV. Quartz-banakite, dike, locality and reference as above. Melville, analyst.

XXV. Monzonite, Predazzo, South Tyrol. Brogger, Eruptivgesteine des Kristiania-Gebietes, II. 

Die Eruptionsfolge der triadischen Eruptivgesteiue bei Predazzo in Siidtyrol. Kristiania, 18t>5, p. 25.

XXVI. Monzonite, Sasinathal, Predazzo. Brogger, loc. cit.

XXVII. Monzonite, Beaver Creek, Bearpaw Mountains, Mont. Weed and Pirsson, Am. Jour. Sci., 

4th series, Vol. I, p. 357. Stokes, analyst.

XXVIII. Monzonite, Monzoni, S. Tyrol. Brogger, op. cit., p. 24. Schmelck, analyst.

XXIX. Monzonite, Yogo Peak, Montana. Weed and Pirsson, Am. Jour. Sci., 4th series, Vol. I, p. 

357. Hillebrand. analyst.

XXX. Monzonite, Mulatto, Predazzo, S. Tyrol. Brogger, op. cit., p. 25.

XXXI. Monzonite, Malgola, Paedazzo, S. Tyrol. Brogger, loc. cit.

XXXII. Monzonite, Predazzo, S. Tyrol. Brogger, loc. cit.

XXXIII. Monzonite, Blansko, Miihren. Brogger, op. cit., p. 50.

XXXIV. Monzonite, Hodritsch, Hungary. Brogger, loc. cit.
EANSOME.] OROGENIC MOVEMENTS.

THE EVIDENCE OF THE LAVA FLOWS AS REGARDS 

OROGENIC MOVEMENTS.

The length of the Table Mountain flow and its favorable position 

with reference to the present drainage system suggested the comparison of its grade profile with those of the Stanislaus Eiver, including 

its North and Middle forks, shown in PI. II. The upper curve in the 

diagram is that of the base of the Table Mountain flow. Below it are 

the curves of the main Stanislaus Eiver with its two principal branches, 

the lower grade being that of the larger Middle Fork. All the profiles 

are projected upon a vertical plane parallel with the .upper and lower 

edges of the map a method which, while it exaggerates the actual 

grade of certain portions of the streams, has the advantage of referring them all to the standard of an ideal consequent stream running 

straight down the slope and allows the direct comparison of one with 

another.

The curves as drawn for the existing streams are dependent upon 

the accuracy with which the canyon contours are laid down on the 

topographic sheets, while the profile representing the bottom of the 

lava stream as now dissected is in general somewhat higher than 

the true bottom of the channel down which it flowed. But the possible error from both sources is probably not large enough to affect 

seriously the general results to be deduced from a diagram on the scale 

shown.

The most noticeable fact that appears upon a comparison of the different profiles is the remarkable regularity of the Neocene curve as compared with the curves of the present streams. When there is recalled 

the great variety of rocks upon which the Table Mountain latite 

rests, tliis even character of the curve indicates that the stream 

which the lava displaced had been highly successful in establishing 

itself upon a uniform grade. In contrast with this profile, the profiles 

of the modern.streams show some irregularities. The curve of the 

North Fork is approximately parallel along its middle portion with that 

of the Middle Fork; but near its junction with the latter stream it 

becomes considerably steeper, probably on account of the fact that, 

owing to its greater volume, the Middle Fork has been able to corrade 

its. channel more rapidly than the North Fork, so that the latter stream. 

is at present being lowered near its mouth at a rate too rapid to allow 

of a corresponding compensation along its entire course. At its upper 

end, also, the curve of the North Fork departs from its parallelism with 

that of the Middle Fork, rising rather suddenly and becoming slightly 

convex. This is due, no doubt, to the weakening of the stream near 

this point by a splitting up into head-water ramifications which are 

individually too feeble to cut deep gorges. In the case of the Middle 

Fork there is no very decided convexity shown, as the stream is much 

longer and carries its gorge farther back into the range. It is interest-
70 LAVA FLOWS OF THE SIERRA NEVADA. [BULL.89.

ing to note that the profile of the Neocene channel also exhibits a slight 

convexity in the upper regions, as if it, like the North Fork, were 

approaching its former head-water drainage. But too little is known 

of the extent and distribution of the latites to the eastward to draw 

any valuable conclusion from this change in curvature.

The curves, as they stand, give evidence that the Neocene stream bed, 

down which a portion of the lavas flowed, records the work of a more 

nearly graded stream than either of its modern representatives, the 

Middle and North forks of the Stanislaus. It probably flowed, therefore, on a lower grade than the existent rivers, and the present difference of 2,500 feet between the bed of the Middle Stanislaus and the 

bottom of the Table Mountain flow in the region of the Dardanelles is 

less than the minimum amount of elevation of this portion of the Sierra 

slope since the date of the latitic eruptions. Moreover, the great 

regularity of the Neocene curve indicates that the elevation of this 

region was effected by a movement or movements which have resulted 

in at least a superficial resemblance to a simple block tilting, without 

deformation of the old surface sufficiently great to be appreciable by 

the methods here used. Lindgren,1 on the other hand, in his interesting study of the Neocene, Yuba, and American rivers, farther north, 

found that the elevation was accompanied by deformation, whereby the 

Neocene channels, instead of showing the regular grade profiles of their 

modern representatives, appear "to be composed of two curves, with 

the convex side upward." As the district studied by Lindgren is some 

hundred miles north of that here described, there is no necessary conflict 

in the different results arrived at in the two fields.

The channel down which the latite flowed was, as has been shown 

in the preceding pages, cut during the volcanic period as a whole, 

and belongs in time with the "intervolcanic channels" of Lindgren, 

and is therefore younger than the channels of the Neocene Yuba

and American rivers, which antedate the main volcanic eruptions. It 

therefore records only a fraction of the differential uplift during Neocene time. According to Lindgren, the intervolcanic channels of the 

region described by him exhibit the marks of an erosive activity similar to that of the present day, and are marked by strong grades in 

whatever direction they flowed.2

The Table Mountain channel seems, however, to have been of a 

slightly different class, and to have been occupied by a long consequent 

stream of more nearly uniform grade than the present rivers, indicating a considerable interval of erosion between the different andesitic 

eruptions. The fact that it, on the whole, follows the course of the 

present Stanislaus, or bisects the angle of its two main branches, indicates that the tilting of the slope has been substantially constant in 

direction since the beginning of Neocene time.

JBull. Geol. Soc. America, Vol. IV, 1893, p. 297. 

2 Loc. cit, p. 295.
HANSOME.] SUMMARY OF THE BULLETIN. 71

SUMMARY.

The contents of the preceding sections may be very briefly summarized as follows:

The area embraced by the map is a fairly typical transverse strip of 

the middle western slope of the Sierra Nevada, having been worn down 

to a rough peneplain during the interval between the close of the Juratrias and the beginning of the Miocene. During the Miocene the volcanic eruptions began, which, accompanied by elevation and tilting 

of the peneplain, lasted to the end of the Pliocene. The first eruptions were rhyolitic, followed by the laying down of a great cloak of 

andesitic breccias and tuft's. The deposition of the auriferous gravels 

both preceded and accompanied the deposition of the volcanic material.

The accumulation of the andesitic tuffs and breccias was interrupted 

by at least one period of considerable erosion, during which a long 

consequent stream, the predecessor of the present Stanislaus Kiyer, 

established its channel down the slope, cutting through the volcanic 

cover into the older truncated Bed-rock series along the greater part of 

its course, and ultimately attaining a very uniform grade. This stream 

was subsequently displaced by a heavy now of augite-latite, the Table 

Mountain flow, which, coming from an as yet unknown source near the 

crest of the range, ran down the stream bed to the edge of the Great 

Valley, a distance of more than 60 miles. A second and thinner flow 

of biotite-augite-latite followed, attaining a greater lateral extent, but 

not reaching the length of the first flow. The third, or Dardanelle 

flow, of augite-latite closed the series of latitic eruptions. The volcanic 

period, as a whole, was brought to an end by fresh andesitic eruptions, 

as shown by andesitic breccias resting upon the latites, accompanied 

by a further tilting of the peneplain toward the southwest.

During Pleistocene time the present streams have dissected the Neocene lavas and tuffs, including the latite flows, and have deeply incised 

the Bed-rock series of Jura trias and older rocks.

The Sierra Nevada latites are mineralogically closely related to ordinary andesites, but chemically they stand between the andesites and 

the trachytes. They are higher in alkalies than the andesites; the potash is generally slightly in excess of the soda, and, in the particular 

rocks described, is present chiefly in the uiiindividualized glass when 

no biotite is present.

Rocks of this intermediate chemical composition are fairly widespread, but are characterized by considerable mineralogical variety. 

The name latite is proposed as a convenient designation for this entire 

group of effusive rocks standing chemically between the trachytes and 

the andesites, and corresponding to the plutonic monzonites of Brogger 

and possibly to some of the dike banakites of Iddings and the gauteite 

of Hibsch.

A comparison of the grade profiles of the Neocene stream, down 

which the latites flowed, with those of the present Stanislaus Kiver, 

shows that the elevation of the crest of the Sierra Nevada in this region 

has been such as would be produced by a simple block-tilting without 

perceptible warping.

INDEX.

Pago. 

Agglomerate lava of Fritsch and Reiss,

origin of structure of ............. 43

Alkalies of latites, proportion of......... 10,57

Altitude of the area studied.............. 10

Analyses of rocks, tables of......... 58-59,06-69

Andesite (sanidine-bearing), chemical

analysis of ......................... 66

Andesitic breccia or tuff associated with

latite, petrograpliic character of. 52-55 

occurrence of............ 9,12,18.20,22,23,26

Andesitic trachyte, chemical analysis of. 66 

Apatite of augite-latite,characters of.... 35,47

"Aschen-structur" in rhyolitic tuff, occurrence of-------..-.---.-.._...... 56

Augite of augite latite, characters of..... 29,

31,32,34,35,36,46,47,48 

Augite of biotite-augite-latite, characters

of................................. 38,39,40

Augite andesite, chemical analysis of.... 66

Augite-latite. chemical analyses of.... 57-59,63

columnar structure o ._..... 13,17,23,24

columnar type of (figured)............ 30

occurrence of.._....... .......... 14-28

petrographical characters of... 27-37,46-53 

plate showing microsection of........ 34

spheroidal structure of ............... 23

spheroidal type of (figured).......... 28

Banakites, characters of .................. 65

Bed-rock series, characters of ............ 11

Biotiteof biotite-augite-latite, characters

of............................. 37,37-38,39

Biotite-augite latite. chemical analyses

of....-................ ....- 57-59,66

eutaxitic structure in........... 38,40.42-44

flow structure in ..............'........ 40

green hornblende in................ 38,39,41

inclusions in .................... 37, 38, 40-42

occurrence of.................... 19-23, 25-27

petrographical characters of ......... 37-46

plate showing thin section of --------- 34

rocks from the Troad similar to...... 44

Biotite-dacite, chemical analysis of....... 68

Biotite-vulsinite, characters of........... 62-63

chemical analysis of................... 66

Brogger, W. C., cited.............-.---.--. 60

Chemical analyses o° rocks, tables showing........................... 58-59, 66-69

Ciminite,characters or'.................... 63

chemical analysis of................... 66

Cross, Whitman, cited .................... 63

Dardanelle flow, petrographical characters of .....^....................... 46-52

Dardanelle latite, Asiatic rock resembling ...............................

petrqgraphic characters of...........

Dardanelle type of lava, character and 

occurrence of......................

Dardanelles, description of ------------ 13,

views of (plates).......................

Diller, J. 8.,cited. ................... 11

Dornite,chemical analysis of........------

Drainage of the region, character of.....

Elevation of the area studied.............

Erba, Luigidell',cited.....................

Erosion of the region, character of. 11,14 

Eutaxitic structure, characters of........

Eutaxitic structure in biotite-augite-la 

tite, figure showing................

occurrence of.................... 38,40

Flow structure in biotite-augite-latite....

Fusuliua, occurrence of...................

Gauteite, a possible dike equivalent of the 

latites --...-.-.........-.......-....

Glass in Sierra Nevada latites, character

Of...................-..-.-. ......

Globulites in Sierra Nevada latites, character of ._-__--.........-..........-

Granite, use of term ......................

Green hornblende in biotite-augite-latite, 

occurrence of................... 38

Groundmass of augite-latite, characters 

of ...................... 29-30,30,35,

Groundmass of biotite-augite-latite, characters of............ ............ 37.

Hibsch, J, E., cited on gauteite ...........

Hornblende of biotite-augite-latite, characters of ...........................

Hornblende-pyroxene-andesite, chemical 

analyses of........._...............

Iddings, J. P., cited........................

Iddingsite in divine-basalt, occurrence 

of............................... .

Inclusions in biotite-augite-latite.- 37, 38,

Jaggar, T. A., cited........................

Kemp, J. F., cited..........................

Klein, J. F. C., cited.......................

Kiich, R., cited ............................

Labradorite of augite-latite, characters 

of .. 29, 30, 31, 32, 34, 35, 36,46,47,48,

Labradorite of biotite-augite-latite, characters of.... ........................

Latite, derivation of name................

petrographical characters of .----'....

Latite (vitrophyric), chemical analysis of

73

50 

46-52

14

24-36 

14,33 

,44,56

07 

12-13

10

4.3

,21,26 

42-43

34

i, 42-44 

40 

18

65

49

48-19 

13

.39,41

48-49

38, 41

65

38,41

67

62, 05

52-53 

40-42 

51 

43 

61 

43

41

10,64 

27-37

66
74 INDEX.

Page. 

Latites, alkali content of.................. 10,5"

character of glassiu .................. 49

character of globulites in............. 48-49

chemical composition of............ 57-59,66

classification of........................ 59-68

compared with vulsinites......... _. 62,64

distinctive chemical features of.. _ 10 

mineralogical variation in............ 62,64

occurrence and distribution of....... 14-27

petrography of.... ........ ...... 27-46

plate showing microsections of..... 34

Lawson, A. C., cited__........_.....; 52

Levy, Michel, cited......... .__..._ 42

Magnetite of biotite-augite-latite, charactersof.................................. 38,40

Monzonites, chemical analyses of...__.. 67 

relations of latites to ....._...._. 65

Olivine of augite-latite, characters of?... 29, 

30, 31, 32, 34,35, 36 

Olivine of Dardanelle lava, characters

of ........................... 46,47,50,51

Olivine-basalt associated with latite,

analysis of.................. .... 58-59

iddingsitein........................... 52-53

occurrence of................:......... 24-25

petrographical characters of....._. 52-53

Olivine-bearing andesitic trachyte, chemical analysis of....._......__ 66

Orog'enic movements, evidences of the

lava flows concerning.-.----._..._ 69-70

Orthorhombic pyroxene of biotite-augite-latite, occurrence and characters of..................... 30,40-41,42

Osann, A., cited .........................".. 63

Peneplain of the Sierra Nevada, features

of-'-.. .- . - 11-12,14,21,22,26 

Peperino, characters of................... 44

Physiography of the region, general oatline of.............................. 10-14

Piperno, supposed origin of structure of. 43 

Piperno structure, figure of latite showing .......................A........ 34

Plagioclases of augite-latite, characters

of.-.-.........-.-. 28,29,31,32,35,47,48,51

Plagioclases of biotite-augite-latite, characters of............................ 37

Pyroxene (.orthorhombic) of biotiteaugite-latite, characters of-.... 40-41,42

Quartz-banakite, characters of............ 65

chemical analyses of...--._......... 67

Ransome, F. L., cited ..................... 23.52

Reiss (Fritsch and) cited................. 42

Ehyolite associated with latite, characters of......_..................... 55-56

occurrence of I......................... 24

Rhyolitic tuff associated with latite,

characters of ...................... 56

Ricciardi, L., reference to chemical analysis by ....._......__..:......_._.... 61

Rosenbusch, H.,qjted .................... 29,43

Sanidine-bearing andesite, chemical

analysis of .__.................... 66

Smith, G. O., cited ........................ 56

Smith, W.S.T., cited..................... 52

Spheroidal structure in augite-latite, occurrence of---.........._........ 23

Stanislaus River, areas of latite along.... 17-18

map of portion of drainage basin of _. 12 

Table Mountain, views of lava flow of. 20,22,24 

Table Mountain type of lava, character

and occurrence of........ 14-20,21,23

petrographical characters of........ 1. 27-37

Trachytes, chemical analyses of.......... 66,67

Trask, J. B., cited on rocks of Tuolumne

Table Mountain................._ 15-16

Tuffs associated with latite, characters of. 52-57 

Tuolumne Table Mountain, featiires of.. 15-17 

Turner, H. W., cited ...................... 27,30

letter of transmittal by............... 7

Vulsinite, characters of.-......----..._ 61,62

chemical analyses of................... 66

Washington, H. S., cited ................. 18,

30,44,50,52,58,61,62,63,65 

Whitney, J. D., cited................... 12,16-17

Wichmann, A.,citedonpiperno structure

of East Indian andesite............ 43

"Wolff, J. E., acknowledgments to.-.-.... 10

Zirkel, F., cited...................... 29,43,61,63