DEPARTMENT OF THE INTERIOR

BULLETIN

UNITED STATES

GEOLOGICAL SURVEY

3STo. 52

WASHINGTON

GOVERNMENT PRINTING OFFICE 

1889

UNITED STATES GEOLOGICAL SUKVEY 

J. W. POWELL, DIRECTOE

SUBAERIAL DECAY OF ROCKS

OF THE RED COLOR OF

BY

WASHINGTON

GOVERNMENT PRINTING OFFICE 

1889

CONTENTS.

Page. 

Letter of transmittal................ ..................................... 9

Introduction........ ............................... ~.... ................ 11

I.

Subaerial decay of rocks .................................................... 12

Decay of the crystalline rocks of the Piedmont region.................... 12

Decay of the rocks of the Newark system................................ 15

Decay of the rocks of the southern Appalachians......................... 18

Decay of the rocks of the Great Appalachian Valley...................... 20

Absence of decayed rocks in the arid region of the Far West.............. 26

Subaerial decay in other countries ....................................... 28

Conditions favoring the decay of rocks............................ 1...... 30

Effects of geologically recent orographic movement on the distribution of

residual deposits in the Appalachian region.......................... 34

The soluble portions of rocks............................................ 37

Characteristics of residual clays ......................................... 39

Economic products of residual clays ..................................... 43

II.

Origin of the red color of certain formations ................................. 44

A hypothesis proposed .................................................. 44

Previous hypotheses ........ ............................................ 47

Exceptions ............................................................. 55

III. 

Re"sum6 .................................................................... 56

. Bibliography ............................................................... 57

Index ...................................................................... 63

(537)

ILLUSTRATIONS.

Page. 

PLATE I. View of Mount Mitchell, North Carolina; looking north along the

crest of the Black Mountains. Roan Mountain in the distance. 16 

II. New- Found Mountains; looking southwest from Asheville, N. C. 20

III. View of fields oi'residual clay, near Natural Bridge, Virginia; looking north. House Mountain in the background................ 26

IV. Mayo River, North Carolina; illustrating the manner in which 

the rivers of the Piedmont region' are eroding their beds. The 

rocks producing the rapids are Newark sandstones.......... 34

V. View from Harper's Ferry, W. Va., looking down the Potomac ; to 

illustrate the manner iu which the rivers of the Appalachians are 

eroding their beds...... ....................................... 36

(539)

LETTER OF TRANSMITTAL

DEPARTMENT OF THE INTERIOR,

U. S. GEOLOGICAL SURVEY, 

Washington, D. £., October 12,1888.

SIR: The observations on which the conclusions presented in the 

following pages are based were made principally during the summers 

of 1885, 1880, and 1887, in the Appalachian region south of Pennsyl- 

- variia. This paper was presented for publication in the fall of 1887, but 

owing to a delay in printing I have been enabled to revise it during 

the present month and include certain observations made during the 

past summer.

In April, 1885, I began geological field work at Knoxville, Tenn., 

.and traveled eastward across the Appalachians to Chester, S. 0., whence 

my investigations led me northward through North Carolina and Virginia to the Potomac Eiver. This field work lasted until late in October and enabled me to visit all of the areas occupied by rocks of the 

Newark system south of the Potomac, which were my special subject 

of study. In April, 1886,1 resumed field work at Leesburg, Va., where 

I had disbanded my party the previous October, and carried examinations as far north as the Pennsylvania-Maryland boundary. As it was 

not deemed advisable to continue the study of the Newark system until 

satisfactory maps could be had of the regions it occupies, a field for 

geologic work was assigned me in Alabama and Georgia.

To reach this field I made a journey through the great valley which 

skirts the Appalachian Mountains on the west. As this valley is a 

marked feature, both topographically and geologically, all the way from 

New York to central Alabama, and is an important part of the Appalachian uplift, I shall speak of it in its entirety as the Great Appalachian Valley a name applied to it by W. B. Eogers in discussing the 

physical structure of the Appalachians, and adopted by Arnold Guyot 

and others. In my journey south I traversed this valley, with various 

departures to points of geological interest, from Pennsylvania to central Alabama, having always in mind various problems relating to the 

subaerial decay of rocks. Finally, late in the season, my work led me 

into central and northern Georgia, where an opportunity was presented

(54:1) 9
10 LETTER OF TRANSMITTAL.

for observing the decay of the crystalline rocks forming the extreme 

southern end of the Appalachians.

In the spring of 1887 I resumed field work in Alabama and Georgia, 

and spent five mouths in the completion of a geologic section 30 miles 

broad, extending from the undisturbed carboniferous rocks ol northwestern Alabama to the uietamorphic schists of central Georgia. 

While traveling by rail to begin this work I stopped at Charlottesville, Va., Greenville, S. 0., and Atlanta, Ga., for the purpose of examining the residual deposits at those localities.

The results of iny observations during these various journeys, so far 

as they relate to the subaerial decay of rocks, are here presented. This 

subject was incidental to other geologic work, and was not the prime 

object of the journeys mentioned ; yet it claimed a large share of attention for the reason that the records of decay are everywhere to be seen, 

not infrequently to the entire concealment of the general geology of the 

country. The journeys mentioned were made on horseback and on 

foot, with the .aid of camping outfit, thus securing unusual advantages 

for observation. I. record the manner of traveling and the routes followed in order to indicate to some extent the character of my observations, as well as the degree of confidence to be placed in the conclusions 

drawn from them.

The field season just closed necessitated a journey through portions 

of Colorado, New Mexico, Arizona, California, Nevada, Wyoming, and 

Dakota, during which the various questions relating to the disintegration and decay of rocks received as much attention as could be given 

them without detriment to other work. 

I remain, very respectfully,

ISRAEL C. KUSSELL,

Geologist.

Hon. J. W. POWELL,

Director U. S. Geological Survey.

(542)
SUBAERIAL DECAY OF ROCKS AND ORIGIN OF THE RED 

COLOR OF CERTAIN FORMATIONS.

BY ISRAEL C. EUSSELL.

INTRODUCTION.

In Part I of this paper attention is directed to the widespread decay 

of the surface rocks throughout the Appalachian region south of the 

southern limit of the glaciated area of northeastern America. It is 

shown also that rock decay is far more advanced in the southern thau 

in the central and northern Atlantic States and increases gradually 

southward. This variation is thought to be due to climatic causes, combined with recent orographic movements which have accelerated denudation in the northern portion of the region under discussion. From 

a brief review of geographical distribution of residual deposits in 

various regions, together with other considerations, the conclusion is 

drawn that rocks decay most rapidly in warm, humid climates.

In Part II it is shown that iron-stained sands resulting from the 

subaerial decay of crystalline rocks agree in many ways with the similarly iron-stained sands forming certain geologic formations, of which 

the sandstones of the Newark system are an example. This, in connection with other facts, leads to the hypothesis that certain sandstones 

and shales, the grains of which are covered with ferruginous incrustations, received their red color during the subaerial decay of the rocks 

from which they were derived.

The name Newark system, proposed by W. 0. Kedfield in 1856, is 

adopted in this paper instead of Triassic, Jurassic, Jura-Trias, etc., to 

designate the formation composed mainly of red sandstones and shales, 

which occurs in detached areas along the Atlantic border from Nova 

Scotia to South Carolina.1

The bibliography at the end of this paper contains a list of publications consulted relating to the decay of rocks.

Reasons for using this name are given in The American Geologist, vol. 3,1889, pp. 

178-182.

(543) 11
12 SUBAERIAL DECAY OF ROCKS. iBULL.52.

I. SUBAERIAL DECAY OF ROCKS.

The formation of soils by the decomposition of rocks in place has 

already received a large share of attention, but recent observations 

suggest that changes of this nature have a wider geological bearing 

than has generally been assigned them, and that questions relating to 

the origin and distribution of soils and subsoils may still be discussed 

with profit.

DECAY OF THE CRYSTALLINE ROCKS OF THE PIEDMONT REGION.

In traveling south froni the southern margin of the moraines left by 

the Pleistocene ice sheet of northeastern America, along the belt of 

crystalline rocks bordering the Appalachian Mountains on the east, the 

surface exposures exhibit greater and greater evidences of decay as one 

proceeds.1 In Pennsylvania and Maryland the mica schists and allied 

rocks are frequently disintegrated to a depth of many feet, so that they 

may be removed with a pick and shovel. The strata, however, are for 

the most part simply broken down, so far as is apparent to the eye, 

although chemical alteration, especially of the feldspars, has unquestionably occurred. With the exception of a few feet at the surface, 

however, it is principally disintegration, i>ot decomposition, that has 

taken place. In a handful of fragments the eye immediately determines the character of the rock from which they were derived ; if chemical change was far advanced this would not be the case. It is difficult to ascertain the depth of this alteration, but in general it may be 

taken at from fifteen to thirty feet; localities are not uncommon, however, where well-marked disintegration has reached a depth of fully 50 

feet below the surface. Typical examples of residual clay the extreme result of subaerial decay are not common in this portion of the 

Appalachian belt, but may occasionally be seen in railroad cuts and 

similar excavations.

As one travels south from the Potomac a great increase is seen in the 

extent and in the depth of the chemical changes that have affected the 

outcrops. Throughout nearly the entire area underlaid by crystalline 

rocks in Virginia and the Carolinas east of the Blue Ridge the soil is 

red clay, which is a residual deposit produced by the subaerial alteration of the rocks on which it rests. Over large areas this alteration 

reaches more than a hundred feet below the surface, but, owing to lack 

of exposures, its full extent is seldom seen.

1 The observations on the decay of rocks presented in this paper refer principally 

to-changes that are obvious to the eye, and not to the alterations frequently detected 

when thin sections of apparently sound rocks are examined with a microscope.

(544)
UUSSELL.] RESIDUAL CLAYS IN NORTH CAROLINA. 13

The depth at which decayed rocks have been observed assures us 

that the downward limit of the changes produced in rocks by atmospheric agencies is not always determined by the level of stream erosion, 

or even by the horizon of the ocean surface. This may perhaps be due 

to recent subsidence, which has depressed the decayed rocks below the 

level at which the alteration took place, for it is evident that the changes 

due to atmospheric influences are of a different character from those produced by the circulation of water through rocks at great depth, although 

there is no sharp line of dernarkation between the two processes.

In cuts along the line of the Carolina Central Eailroad east of 

Wadesborough, oa the Cape Fear and Tadkin Valley Eailroad near 

Jonesborough, and along the North Carolina Eailroad west of Ealeigh, 

4ST. C., fine sections of decomposed crystalline rocks are exposed. These 

are but isolated examples, however, of what can be seen over thousands of square miles ia the great area of crystalline rocks in which 

they are situated.1 At the localities cited above the rocks retain little 

of their original character, but are now variously colored clays, which, 

when moist, can be molded in the fingers or cut with a pocket-knife. 

In many places the layers of granite, mica schist, hornblende schist, 

talcose schist, and similar rocks have been twisted and folded so that 

in their present eroded condition the bedding in the outcrops is nearJy 

perpendicular. In such instances, when the rock is excavated, as in 

railroad cuts (the best example I observed is at Gary, eight miles west 

of Baleigh), the entire mass, to a depth exceeding fifty feet, is a soft, 

plastic clay, which reveals its original stratification and lamination by 

an almost infinite number of vertical bands and lines of various tints 

and shades. Bright red and brilliant yellow predominate, but these 

harlequin tints are many times blended with gray, purple, and white 

in such a way as to produce most remarkable examples of natural coloring. An analysis of a characteristic sample of this residual clay, 

apparently derived from chloritic schist, gave the following result:

Analysis of residual clay. By R. B. Riggs.

Silica (Si'02 ) ........................................ 54.54

Alumina (A13O3 )...... .............................. 26.43

Ferric oxide (Fe2O3 )................................. 9.04

Water (H20)........................................ 9.87

Total.................. .....................:. 99.88

1 Other localities have been noted by L. S. Burbauk, Proc. Boston Soc. Nat. Hist., vol. 

16, pp. 150-155; and by W. C. Kerr, Am. Jour. Sci., 3d series, vol. 21, 1881, pp. 345-358. 

The formation of soils by the decomposition of crystalline rocks in Alabama has been 

well described by Eugene A. Smith in the Geol. Survey Alabama, Rept. for the years 

1881 and 1882; and by \VilUam C. Stubbs in Berney's Handbook of Alabama, pp. 147 

et seq.

(545)
14 SUBAERIAL DECAY OF RuCKS. [BULL. 52.

About Greenville, S. 0., the character of the residual deposits resulting from the subaerial decay of highly micaceous gneiss may be 

observed. The deep-red color of the plowed fields, merging at times 

into broad areas of yellow, to be seen in early spring, together with the 

exposures of decayed rock in railway cuts and along carriage roads, 

shows that this region has not escaped the decay and leveling effects of 

atmospheric erosion. The exposures of residual de"bris are not remarkable, however, as compared with typical localities in North Carolina and 

Virginia, for example, and seldom exceed forty or fifty feet in depth. 

The rock in the stream beds is quite compact, although presenting indications of considerable chemical change. This portion of South Carolina, in common with other areas in the southern Appalachians, forms 

an apparent exception to the rule that the residual deposits of the Atlan-* 

tic States increase toward the south. As will be shown a few pages 

farther on, this exception is explained by the conditions of erosion 

which obtained in some portions of the Southern States.

In regard to the widespread decay of the crystalline rocks of South 

Carolina we have the testimony of M. Tuomey, whose conclusions in 

this connection of some forty years' standing can "not be questioned, as 

is shown by the following quotation:

There is scarcely anything more striking in the face of the country in this [western] 

part of the State than the great extent and depth to which disintegration of the rocks 

has proceeded. Were it not for the occasional blocks of granite that lie scattered here 

and there, a person whose observations were confined to the surface would scarcely 

suppose himself traveling over the upturned edges of a series of rocks. 1

The quartz veins so common throughout the crystalline areas of Virginia, the Carolinas, etc., are more durable than the rocks inclosing 

them, and retain their integrity long after the associated schists have 

changed to plastic clays. Bowlders and pebbles derived from the 

breaking up of quartz veins cover the surface with a continuous sheet

of de'bris over large areas, forming a residual deposit, the origin of 

which is revealed at a glance. The quartz itself, although opposing 

great resistance to disintegration, is not indestructible, as is shown by 

the brown, iron-stained lines that traverse it in every direction, marking the course of incipient fractures. The continual breaking of the 

quartz into smaller and smaller fragments produces an angular sand 

which everywhere forms an ingredient of the red clay soil.

When average samples of residual deposits left by the decomposition 

of crystalline rocks are agitated in water more or less angular . fragments of quartz and feldspar, with scales of mica and fragments of 

other minerals, are usually obtained. This material differs with variations in the character of the parent rocks and with variations in its 

degree of decomposition. On examining these residual sands with the 

microscope, especially in cases where the decomposition is well advanced, it has been found that each grain is coated with a thin shell

'Report on the Geology of South Carolina, Columbia, S. C., 1848, p. 98.

(546)
RUSSELL/) CAUSE OF THE COLOR OF RESIDUAL CLAYS. 15

having a brownish or red color. Prolonged washing fails to remove 

this superficial coating, a fact which is well illustrated by the color of 

the sands deposited by the streams of Virginia and the Carolinas in 

the regions underlaid by crystalline rocks. Hot hydrochloric acid dissolves the coloring matter, however, and leaver the grains of quartz, 

feldspar, etc., with their normal tints. It has been determined from 

chemical analyses of a number of samples of partially decomposed 

crystalline rocks that the incrustation which gives the grains their characteristic color is rich in both ferric oxide and alumina, and may perhaps be best described as a ferruginous clay. It is therefore evident 

that the predominant red color of residual deposits is due to a coating 

consisting largely of ferric oxide deposited during the disintegration 

and decomposition of the parent rocks, around the individual grains 

into which the rock becomes divided in weathering. 

It may be remarked in passing that the residual deposits covering

large portions of the crystalline areas of Virginia, the Carolinas, Georgia, and Alabama are sufficiently auriferous in many localities to be of 

economic importance.

The decay of the rocks in the southern Atlantic States has been observed by many travelers and has been the subject of a number of essays, 

as may be seen by turning to,the bibliography at the end of this paper. 

Among the many contributions lo the subject, one of the most definite 

and instructive is by T. Sterry Hunt, 1 who, in writing on the lithology 

of the southern Appalachian region, says :

The rocks are covered often to a depth of a hundred feet or more by the undisturbed 

products of their own decomposition, the protoxide bases having been removed by 

solution from the feldspars, the hornblende, and the whole rock, with the exception 

of the quarfczose layers, reduced to a clayey mass, still, however, showing inclined 

planes of stratification.

Similar testimony is furnished by W. M. Fontaine,2 who states that 

The depth to which decay has penetrated here [in the granites and gneisses near 

Richmond, Va.] is far less than in the southern and southwestern parts of the State. 

In the latter we find strata not speci ally prone to decay often decomposed and changed 

to a loose earth for fifty and even one hundred feet.

Descriptions of the surface decay of the rocks of the southern Appalachian region by other observers might be quoted, but enough has 

been presented for the purposes of this paper.

DECAY OF THE ROCKS OF THE NEWARK SYSTEM.

In the rocks of the Newark system in Virginia and North Carolina 

a widespread decomposition, similar to that affecting the older rocks 

of the same region, was observed at many localities.

The brecciated conglomerate which is found wherever the bottom of 

the Newark system is exposed is composed of both rolled and angular

1 Chemical and Geological Essays, 1871-1873, pp. 187,250.'

"Notes on the Mesozoic of Virginia, Am. Jour. Sci., 3d series, vol. 17, 1879, p. 30.

(547)
16 SUBAERIAL DECAY OF EOCKS. [BULL. 52,

fragments of the adjacent crystalline rocks. These were compact and 

solid when deposited as pebbles and bowlders, but they are now often 

as thoroughly disintegrated and decomposed as the neighboring rocks 

described above. In a cut on the line of the North Carolina Railroad, 

10 miles west of Wadesborough, there is a fine exposure of the basal 

conglomerate of the Newark. The north side of the excavation still 

stands as a perpendicular wall about twenty feet high, in which the 

variously shaped fragments composing the brecciated conglomerate are 

clearly distinguishable. At a little distance the rock appears almost 

identical with the Potomac marble, with which it agrees in geological 

position. On examining more closely, however, one is surprised to 

find that it is completely decomposed, and that, when moist, it can be 

cut with a pocket knife, through pebbles and matrix alike, as easily 

as so much potter's clay. The full depth of the alteration in this instance is not revealed, but it extends more than thirty feet below the 

surface without change in character. Most of the pebbles observed 

were formed of talcose schist and the cementing material was apparently 

derived from rocks of the same composition.

In the ordinary brown sandstones and sandy shales of the Newark 

system throughout Virginia and North Carolina but little subaerial 

decay is apparent to the unassisted eye, except in the grains of feldspar which they contain. Some of the strata in this formation are 

composed of plastic red clay, but whether this was deposited in its 

present condition or is the product of subsequent decay it is not always 

possible to decide.

The most remarkable example which I observed of the change that 

rocks undergo when long exposed to the atmosphere occurs in the 

trap dikes traversing the Newark system of North Carolina. These 

are composed of dolerite of the same character as the " traps" so 

abundant in New Jersey and in the Connecticut Valley, and are exceedingly numerous throughout the various Newark areas south of 

the Potomac. In a single section, 13 miles in length, of the Newark 

area which crosses Auson County, N. C., over fifty trap dikes were 

observed, varying from a fraction of a foot to seventy-five feet in width. 

It is probable that many others exist which escaped notice.

These dikes trend approximately north and south and are nearly 

vertical in dip. They are usually undistinguishable in the topographic relief of the region, but their presence is occasionally indicated 

on the surface by long lines of weathered trap bowlders. Sections of 

the dikes may frequently be observed in railroad cuts, and in such 

instances it is found that decomposition has reached to a great depth. 

In fresh sections forty or fifty feet deep the decomposition extends 

to the bottom of the exposures, without any indication of approaching its lower limit. Many dikes are completely decomposed throughout, and the originally hard, tough, bluish dolerite, which would ring 

under the hammer, has been transformed, into a yellowish, clay like

(548)
BULLETIN NO. 52 PL. I

,...<-"j^J6*-s>. 

'" -k-V'';

- - '-liF^'" '->;.- ' --' - ' '" " { ' '^^^ '?"$*"-: /'V' " t .<: >, 

'"^^:ff\:':.t >Ji -^ d r>»;" *' -""wjfe:-"?! l-^'v-- i'-,

§\ ' '' " "''',^^ - ft'A"' .- *"u ^ 

s^

i%, «&«*:: ,

7fi^

^^^i^^f'-^; :^':v^^-'-'-lJ

 CAROLINA, LOOKING NORTH ALONG THE CREST OF THE BLACK MOUNTAINS.
RUSSELL.} DECOMPOSED TRAP. 17

mass that can be molded in the fingers and cut like putty. In some 

cases, especially in the larger dikes, the decomposition is only partial, 

and the loose rotten mass contains rounded bowlders in process of 

disintegration, in the center of which the rock still exhibits its original 

characteristics. These bowlders usually occupy the center of a dike, as 

seen in vertical section, but at times there are two or more vertical 

bands of them distributed through the decomposing rock. The sides 

of the fissures through which the trap ascended are hardened or metamorphosed at some localities by the contact of the igneous rock, and 

thus rendered unusually durable. In such instances the trap is often 

completely decomposed, while the walls of hardened sandstone exhibit 

no sign of disintegration.

It is a noticeable fact that wells sunk in or near trap dikes in the 

Newark areas of North Carolina contain unusually "hard" water, 

which is frequently brackish, It may be that the saline matter in 

these wells was derived from salts impregnating the surrounding sedimentary rocks, but they must also receive mineral matter from the decomposing igneous rocks.

In speaking of the trap dikes in South Carolina, which belong to the 

same great system as those just considered, M. Tuomey remarks : l

Both the trap and other rocks with which it is associated are so much disintegrated that it is impossible to observe the form presented by the dikes at the surface. 

I have not met with a single instance where this rock presented anything like an 

escarpment, although the manner in which it penetrates the rocks through which the 

dikes pass may be observed at many places, in ravines and such localities. On the 

surface the dikes are readily traced by the long lines of black or dark green and ferruginous spherical masses of trap scattered along in the direction of the dikes, often for 

miles in extent.

A chemical examination of decomposed trap from a dike near Wadesborough, N. C., shows that it is essentially a kaolin containing about 

seventeen per cent, of ferric oxide. An approximately complete analysis of this material by T. M. Chatard is given below, together with the 

average composition of eight samples of unaltered dolerite from New 

Jersey and the Connecticut "V alley, as determined by G. W. Hawes.2 

The trap rocks are, in general, so nearly identical throughout the Kewark system that we may consider this average as representing very 

closely the composition of the rock from which the residual clay described above was derived. It will be seen by the comparison that a 

large part of the silica, as well as of the more soluble portions of the 

Original rock, has disappeared from the residual deposit, while the 

relatively insoluble alumina and ferric oxide have greatly increased 

their percentages.

1 Report on the Geology of South Carolina, Columbia, S. C., 1848, pp. 65, 66. 

* Am. Jour. Sci., 3d series, vol. 9, 1875, pp. 185-192 [the analyses used are on pp. 

186,187,189].

(549) 

Bull. 52 2
18 SUBAERIAL DECAY OF KOCKS.

Analyses of dolvrite.

[BULL. 52.

Constituents.

Silica (SiOs).--... ................

Manganoua oxide (MnO) .... ......

Lime (CaO) ...... ...... ...... ....

Soda (Na30). .....................

Potash (K20).... .................

Phosphoric acid (PaOs).... ........

Titanic acid (Ti02 ) ...... ...... ....

Water (by ignition) (H2 0).... ....

Total.......................

Average composition of 

unaltered dolerite.

52. 50

14.15

9.24

1 Qfi

0.45

10.03

7.48

2.30

0.69

0.14

0.92

99.86

Decomposed 

ilolerite 

f rom Wades 

borough. 

N.C.

39.55

28.76

16. SO

Trace.

0.37

0.59

Trace.

Trace.

Trace.

0.10

0.64

13.26

100. 07

In following the rocks of the Newark system south from Pennsylvania, through Maryland, Virginia, and the Carolinas, one finds the trap 

dikes exhibiting greater and greater evidences of decomposition. 

Thus, as in the case of the Archaean granites and schists and the Newark conglomerates, the decay of the eruptive rocks increases towards 

the south.

DECAY OF BOOKS IN THE SOUTHERN APPALACHIANS.

Subaerial decay is marked among the mountrins of western North 

Carolina and eastern Tennessee, where the material filling the valleys, 

as in the lowlands to the eastward, is usually a red clay, in which 

angular fragments of quartz, feldspar, and mica are intermingled. 

All the stages in the formation of this material from the underlying 

schists and associated rocks may be observed at many localities. 

The same is also true of large portions of the mountainous region of 

Georgia and Alabama. In the area underlaid by Ocoee schists, however, 

which borders the more intensely metamorphosed rocks of the southern 

Appalachians on the west, transportation is being carried on so rapidly 

that comparatively little residual material remains. The reason of the 

more energetic action of the streams in this region is to be found in the 

fact that the limestone rocks bordering the Ocoee formation on the west 

are much more easily removed than the less soluble slates and schists 

of the metamorphic area; hence the latter stand in relief and impart 

a high, grade to the stream channels which lead from them, The

(550)
RUSSELL.] APPALACHIAN SCENERY. 19

streams are consequently rapid, and the surrounding slopes are in many 

places stripped of their residual deposits.

Throughout the southern Appalachians we find abundant illustration of the rounded summits and flowing outlines characteristic of a 

land that has been long subjected to decay, and in which decomposition and disintegration in general exceed transportation. Even in the 

most elevated portions of this range, however, the scenery is subdued 

and pleasingly picturesque, partaking rather of the beauty of hills 

overlooking pastoral valleys than of the rugged grandeur of mountains such as the Sierra Nevada and the Alps. To the geologist these 

differences appear to be wholly due to variations in the balance between disintegration and transportation. The mountains of the southern Atlantic States have a softness of outline and a delicacy of 

tint peculiarly their own, which depend largely on the luxuriance of 

the vegetation with which they are clothed, and on the vapory atmosphere with which they are surrounded. The charm of their beauty can 

not be shown in ordinary illustrations, but must be seen and felt to be 

understood. The flowing outlines of the hills and something of the 

atmospheric effects of the climate of the South may be gathered from 

the accompanying picture of the New Found Mountains, as seen from 

near Asheville, N. C.

Another convenient locality for studying the effects of atmospheric 

forces on crystalline rocks is furnished by the street excavations and 

suburban improvements of Atlanta, Ga. In every direction about that 

city the evidence of deep rock decay is to be seen, and the landscape 

presents the subdued outlines characteristic of " topographic old age."

In describing the formation of soils by the decay of the metarnorphic 

rocks of eastern Alabama (and the observation would apply equally 

well to large areas in Georgia), E. A. Smith observes i 1

In some parts the strata have undergone complete disintegration in place, and 

have been converted into great masses of stratified clays, infcerlamiuated with seams 

of quartz, which, gradually broken down, cover the ground with their angular fragments. . The depth to which this decay reaches depends on the nature of the rock and 

its position, and in many instances even twenty or thirty feet below the surface the 

rock is still decomposed.

In the region mentioned in the last paragraph two varieties of soil, 

termed red and gray, are recognized by the author quoted:

The soil of the red lands is derived from the decomposed hornblendic gneisses and 

slates, which in many places, where exposed in washes or gullies, are seen to be mere 

stratified clays, containing fragments, more or less angular, of the quartz veins or 

seams which are nearly always interbedded with the other rocks of this region. The 

top stratum of this soil, from two to three inches in depth, has often a dark chocolatebrown color, but below it becomes a bright red, and at varying depths, from ten to 

fifteen feet, becomes a yellowish hard clay. Where the freshly decomposed rocks are 

seen the color is yellowish rather than red, the latter color being darker and more inSurvey Alabama, Kept, for 1881 and 1882, p. 184. 

(551)
20 SUBAERIAL DECAY OF ROCKS. FBULU 52.

tense apparently the further removed the soil is from its original position and the 

more it is affected hy the decay of the vegetable matter.

The gray soils result from the disintegration of gneisses aud mica slates, which 

contain comparatively little or no hornblende or other iron-bearing minerals. They 

are commonly somewhat sandy, usually light-colored, gray to dark gray, sometimes 

nearly black, with very often, however, a decidedly reddish color, similar to that of 

the hornbleudic soils above described. Fragments of the partially decayed gueiss 

of a light-gray color often lie embedded in reddish and even red clays or clayey 

sands. 1

A number of analyses of the soils of the metamorphic region of Alabama, of interest to the student of rock decay, are given in the report 

just cited.

DECAY OF BOCKS IN THE GREAT 'APPALACHIAN VALLEY.

In traversing the Great Appalachian Valley 2 from Pennsylvania to 

Alabama, an increase in the extent and depth of the residual deposits 

toward the south was again observed.

This great valley owes its formation primarily to an upheaval, which 

brought the rocks within the reach of denuding agencies. The present 

topographic diversity, however, is not due to an elevation of the borders of the valley, but to the denudation of its bottom. The removal of 

rocks has been carried on, as usual, by the action of running water, 

but its work has been performed largely by chemical solution. That 

this process is still continuing is shown by the thousands of "sink 

holes" and by numerous valleys without surface drainage, to be seen in 

the limestone areas from Pennsylvania to Alabama. .It is also indicated by hundreds of fine springs, and by numerous caverns, of which 

Luray is a type, which owe their existence to subterranean solution.

Throughout the entire extent of the valley thousands of feet of strata, 

principally of limestone, have been removed. In the Coosa Valley, 

Alabama, which is a portion of the Great Appalachian Valley, the minimum thickness of strata carried away since the Carboniferous period, 

as determined by careful measurements, is not less than eight or nine 

thousand feet. The maximum denudation, of which no accurate determination has been made, may largely exceed this.

l. Survey Alabama, Report for 1881 and 1882, pp. 183-187. 

*The valley referred to occupies for the most part a well-defined position between the 

Appalachian Mountains on the east and a great but somewhat indefinitely defined 

table-land known as the Cumberland, Alleghany, and Catskill plateau on the west. 

It crosses the prevailing corrugations of the Appalachians somewhat obliquely, its 

prevailing trend being nearly northeast and southwest, and in Pennsylvania is to the 

east of the Alleghanies. It has many local names; in Alabama it is occupied principally by the Coosa River, and is known as the Coosa Valley; farther north it is the 

valley of East Tennessee aud the valley of Virginia ; in Maryland aud Pennsylvania 

it is the Cumberland Valley ; in Pennsylvania it becomes the Lebanon and Kittatinny 

Valleys ; in New Jersey and New York it is drained by the Walkill. The upper portion of the Hudson River Valley and the depression occupied by Lake Champlain are 

portions of the northern extension of the same topographic feature.

(552)
1ULLETIN NO. 52 PL. II

 LOOKING SOUTHWEST FROM ASHEVILLE NORTH CAROLINA.
KUS8BLL.] DECAY OF ROCKS IN ALABAMA. 21

The predominant rock of the Great Appalachian Valley is Paleozoic 

limestone. Throughout large areas, especially in Alabama and Georgia, 

this rock is highly charged with magnesia and silica and becomes a cherty 

dolomite. It is in regions underlaid by rocks of this character that the 

most abundant accumulations of residual deposits occur. The chert, 

being slow to decay, accumulates at the surface as the inclosing limestone dissolves away, and, together with the residual portion of the limestone, forms rounded hills and gentle ridges in which rock in place is 

seldom seen owing to the depth of the subaerial deposits. Over large 

areas in Wills and Coosa valleys, Alabama, residual deposits of this 

character have in general a minimum thickness of not less than a hundred feet. Their maximum thickness is probably two or three times as 

great. In regions where the limestone is less silicious the residual deposits are more homogeneous and usually consist throughout of red 

clay, frequently rich in concretionary iron ore,

The red earth, containing angular fragments of chert which have resulted from the decay of maguesian limestone (Knox dolomite) in the 

southern part of the Great Appalachian Valley, is very similar both in 

character and mode of origin to the red earth charged with flints which 

forms the surface over portions of the Chalk formation in the south of 

England, as described by W. Whitaker.1

The chert, or "flint," which occurs in great quantities in the Silurian 

and Carboniferous rock of Tennessee and Alabama, although exceedingly hard and giving every indication of durability when fresh, crumbles 

to.a fine white powder, bearing no resemblance to the original rock, 

when long exposed to the atmosphere. This change has been observed 

to extend to the depth of two or three feet from the surface of a bed of 

chert, which at a greater depth was compact and hard. The change 

from altered to unaltered chert is abrupt, and hand specimens may 

easily be collected in which one-half is a compact, bluish chert, fit for 

gun flints, and the other half a powdery, amorphous mass that crumbles between the fingers. The fact that the entire specimen in such an 

instance was originally homogeneous is shown by the concentric lines 

and bands of various tints that traverse both the solid and the friable 

portions without interruption.

The .soil formed by the decay of the more calcareous portion of the 

magnesian limestone (Knox dolomite) of Alabama is thus described by 

Eugene A. Smith :2

A clayey loam of light yellowish to orange-red colors and of varying thickness, the 

average being perhaps 1| feet. The subsoil is usually heavier, being a rather stiff clay 

or clayey loam of a red or yellow color. Both soil and subsoil are often filled with lumps 

of limonite or brown iron ore. Beneath the subsoil, at varying depths, lies the dolomite, or limestone. There is a great variety in the color of the top soil, between a

J Mem. Geol. Survey Great Britain: The geology of Middlesex, Hertfordshire, etc. 

London, 1864, pp. 63-66. 

2 Geol. Survey Alabama, Kept, for 1881 and 1882, p. 200.

(553)
22 SUBAERIAL DECAY OF ROCKS. [BULL. 52.

very light yellow, almost gray, and a deep red and brown ; but the subsoil is commonly a yellow or red clay, and it is not unusual to find these soils and subsoils, 

especially those of a light color, filled with angular fragments of chert.

Portions of the Silurian rocks of Alabama, readily recognized as limestones when un weathered, are easily mistaken for sandstones and shales 

when only their weathered outcrops can be seen. The Clinton ore, or 

"fossil ore," interbedded with strata of shale and sandstone, forms one 

of the most characteristic beds in the Upper Silurian rocks" of Tennessee and Alabama. In the mines of Gadsden and of Ataila, Ala., 

where Clinton ore is worked, the strata are highly inclined (a dip of 70° 

to 80° to the southeast prevailing) and well exposed for study. The 

outcrops of the beds are of soft, porous, highly fossiliferous ore, which 

has a deep brownish red color and is easily worked and easily smelted. 

The ore at Ataila retains this character to the depth of about two hundred and fifty feet, measured down the slope, and then changes to a 

hard, compact, ferruginous limestone, rich in fossils.1 The marked difference in the character of the ore in thB upper portions of the mines 

as compared with that from the lower portions is due entirely to weathering. This is shown by the general appearance of the ore at various 

horizons and by its chemical composition. Two typical samples of 

the ore, selected by me one from near the surface, representing the 

ordinary character of the soft ore, and the other from a depth of two 

hundred and fifty feet, representing the hard ore, but not the most calcareous variety gave on analysis the following percentages of iron, 

lime, and carbonic acid, after drying at 105° Centigrade:

Analyses of Clinton iron ore. By E. B. Eiggs.

Constituents.

Iron (Fe)... ..............

Lime (CaO). .............

Surface sample.

57.52

1.38

0.30

Sample from 

250 feet below 

surface.

7.75

47 fi4

34. 90

The increase of lime in the Clinton ore of the Great Appalachian 

Valley when followed below the surface is well shown iu the following 

table, compiled from analyses of ore mined near Birmingham, Ala., 

which I copy from a paper by John B. Porter :. 2

The ore is 13 feet thick and highly tilted, with an outcrop which has been located 

for many miles. At the time of the analysis the mine was 130 feet deep on the ore,

!A similar change in fossil ore has been noted by T. H. Dewees, in Pennsylvania ; 

Second Geol. Survey Pennsylvania, Report F, 1878, p. xlvi.

2 "The iron ores and coals of Alabama, Georgia, and Tennessee." Trans. Am. Inst. 

Mining Engineers, vol. 15, p. 189.

(554)
RUSSELL. | CLINTON ORE A RESIDUAL DEPOSIT. 23

and the following figures give the percentage of carbonate of lime for each. 10 feet 

descent:

Percentage of lime in Clinton iron ore.

10 feet below surface . . .

20 feet below surface . . .

30 feet below surface .. .

40 feet below surface . . .

50 feet below surface . . .

60 feet below surface . . .

Trace.

Trace.

Trace.

21.06

23.90

37.01

80 feet below surface . . .

90 feet below surface .. .

100 feet below surface . . .

110 feet below surface ...

120 feet below surface . . .

130 feet below surface . . .

25. 61

29.92

29.89

23. 37

28.82

21.32

.30. 55

At Atalla the change from "soft ore" to'ferruginous limestone, or 

"hard ore," takes place at about the present level of stream drainageAt this horizon the stratum increases from two feet and a half to three 

feet in thickness. This increase in thickness below the level of drainage indicates that the removal of the calcareous portion of the ferruginous strata has allowed the bed to be compressed. As the unweathered ore is of doubtful economic value, owing to its high percentage of 

lime and the difficulty of mining, exaggerated estimates of the impor. 

tanceof the Clinton ore deposits of the South are to be guarded againstThe Carboniferous rocks of eastern Alabama at some0 localities occur 

next above the Clinton, but are usually separated from it by a stratum 

of highly bituminous shale and sandstone, about thirty feet thick. In 

these Carboniferous rocks there are heavy layers of highly silicious 

limestone, abundantly charged with crinoidal remains. In its unweathered condition, which is seldom observed, this is a dark, heavy, 

siliceous rock, in which the fossils are quite obscure. On the surface, 

and usually to the depth of fifty or sixty feet, this rock appears as a 

porous chert, which is traversed in every direction by cavities left by 

the solution of fossils, principally the stems of crinoids. A greater contrast than is presented by the massive black limestone as it appears in 

its uuweathered condition and the light-colored, slag-like chert of the 

weathered outcrops could scarcely be imagined. The debris of this 

peculiar siliceous limestone is found in most of the " red ore ridges'' of 

Tennessee and Alabama, and when its geologic relations are known to 

the miner it furnishes an important aid in tracing the deposits of Clinton ore, with which its association is quite constant.

Many other illustrations of the character and of the extent of the 

weathering which has affected the rocks in the southern part of the 

Great Appalachian Valley, with reference especially to the genesis of 

limonite and manganese deposits, might be enumerated; but enough 

facts have probably been presented for the purpose in hand.

Residual clays of the same character and origin as those which impart their characteristic color to great areas in Alabama and Tennessee

(555)
24 SUBA-ERIAL DECAY OF ROCKS. [BULL. 52.

also occur in that portion of the Great Appalachian Valley which lies 

in Virginia, Maryland, and Pennsylvania. In the northern portion of 

the valley, however, especially north of the James, the clays are not so 

continuous or of so great a thickness as farther south.

Throughout the valley of the Shenandoah and in the region drained 

by the James, New Eiver, etc., in Virginia, the surface of the country 

is covered to a depth sometimes exceeding fifty feet with a red clay 

which has resulted almost entirely from the decay of limestone. This 

is a residual deposit that accumulated at the surface as the limestone 

in which it once formed an impurity was slowly dissolved away. It is 

evidently the product of a very long period of concentration, as the insoluble portion of the limestone in this region constitutes but a very 

small part of its weight. , '

In the following analysis the composition of a sample of light gray 

Trenton limestone from Lexington, Va., is given, together with the 

analysis of a characteristic sample of the superficial red clay of the 

same region, which was left after the removal of the more soluble portions of the limestone.

Analyses of Trenton limestone and of the residue left by its decay. By 

R. B. Rifj<js.

Constituents.

Silica'(Si02 ).. --....-..-.......-,..

Lime(CaO) ......................

Magnesia (MgO )...... ............

Potash (K20)... ....... ...........

Soda (NaaO). .....................

Water (H2 0) .....................

Total. ............ ...... ......

Unaltered 

limestone.

0.44

j 0.42

54.77

Trace.

Not clet'd.

Not det'd.

42.72

1.08

99.43

Residual 

clay.

43.07

i 25. 07

i . 15.16

0.63

0.03

2.50

1.20

12.98

100. 64

An analysis of magnesian limestone (Knox dolomite) from Morrisville, Ala., and of the residual clay left by its decomposition, is here 

inserted, to illustrate still further the chemical changes which occur 

during the decay of calcareous rocks. The original rock in this instance 

was a grayish-white dolomite, typical of its class over a large area in 

the southern part of the Great Appalachian Valley, while the clay left 

by its decay is a fair sample of the red soil of the South.

(556)
KUSSELL.] DECAY OF DOLOMITE. 25

Analyses of dolomite and'of residual clay left by its decay. By 

W. F. HAllebrand.

Constituents.

Silica (SiO2 ).. ....................

Lime(CaO) ......................

Magnesia (MgO) ..................

Potash (KO).... ..................

Soda (Na20).... ..................

Water (H20) .....................

Total ........................

Unaltered 

dolomite.

3.24

0.17

0.17

0.06

29.58

20.84

45.54

0.30

99.90

Residual clay.

55.42

* 22. 17

8.30

Trace.

0.15

1.45

2.32

0.17

19. -6

£IQ H4

With TiOa and P305 . t2.10atlOO°C.

These investigations indicate that approximately from one to four 

per cent.'of ordinary light-colored limestones, depending mainly on the 

amount of silica and alumina they contain, remains behind and contributes to the formation of residual clays when subaerial decay takes 

place. These analyses, however, are somewhat unsatisfactory in this. 

connection, as only a small quantity was used in each instance, and no 

attempt was made to determine the minute portions of various elements 

which might reasonably be expected to be present.

The red earth of the southern portion of the Great Appalachian Valley is apparently identical, both in composition and in the method of 

its accumulation, with the "terra rossa" of southern Europe, the 

"laterite" of India, and the "red earth" of Bermuda, each of which 

will be noticed further on.

The red clay so frequently found in caves, especially in the limestone 

regions of the Southern States, and known as "cave earth," is another 

occurrence of the residual deposits resulting from the subaerial decay 

of rocks, and at times has considerable interest.

Although quantitative measurements of the extent and thickness of 

residual deposits of the Great Appalachian Valley have not been 

made, yet qualitative observations are sufficient to show that, like the 

similar deposits covering the crystalline and Newark areas east of the 

Blue Ridge, they are far more abundant in the South than in the "North, 

as has already been stated, and increase gradually as one travels from 

north to south.

A comparison of the southern Appalachian region with the driftless 

area of the upper Mississippi Valley, as described by T. C. Chaniberliu

(557)
26 SUBAERIAL DECAY OF ROCKS. [BULL. 52.

and E. D. Salisbury,1 shows that rock decay is far more advanced in 

the former region than in the latter. The average of one thousand eight 

hundred measurements of the depth of residual deposits over the driftless area of Wisconsin as given in the report referred to above, is 7.08 

feet, the maximum, which was possibly in an enlarged fissure, being 70 

feet. A general inspection of the southern Appalachian region is 

enough to assure one that residual deposits are there at least ten or 

fifteen tirm-s as thick as the estimated average thickness of the similar 

deposits in Wisconsin, etc. The driftless area described by Chamberlin and Salisbury is characterized by outstanding towers of castle-like 

masses of rock, frequently spoken of as "erosion columns," that have 

been left in bold relief by the removal of the surrounding strata. In 

the Southern States no such records of the former extent of particular 

formations are to be found. Their existence, except in immediate proximity to cliffs, is precluded by the fact that the rate of decay exceeds 

the rate of transportation.

The general rounded character and soft, flowing outlines of a limestone country that has long been exposed to atmospheric decay is illus. 

trated by Plate III, which represents the characteristic scenery between 

Lexington and Natural Bridge, Va. The elevated table-land in the 

background of the picture is House Mountain, which overlooks Lexington.

The increase of residual deposits toward the south in the Appalachian region is a geologic feature of interest, and one that demands 

explanation. A discussion of this question will be postponed for a few 

pages, however, in order to present something of the effects of subaerial decay in other regions, and to state the nature of the chemical 

changes ^'hich take place in rocks when exposed to atmospheric influences.

ABSENCE OP DECAYED ROCKS IN THE FAR WEST.

Nothing comparable with the extensive disintegration and decay of 

the rocks forming the southern portion of the Appalachian Mountains has been observed by me during somewhat extended journeys 

through other portions of the United States. In the Northeastern 

States the records of such decay are mostly obscured and obliterated 

by glacial deposits. West of the Mississippi, in New Mexico, Colorado, Idaho, Utah, Nevada, Oregon, arid California, only secondary 

glaciers originating from local centers existed during the glacial 

epoch. The rocks in large portions of this region have presumably been subjected to subaerial influences fully as long as in the 

South Atlantic States, but no marked evidences of general decay are 

to be seen. In the mountains of the Far West, which, as nearly as I 

can judge, may be fairly compared with the more elevated portions

1 U. S. Geol. Survey, Sixth Ann. Kept., p. 205. 

(558)
BULLETIN NO. 52 PL. Ill

NATURAL BRIDGE, VIRGINIA, LOOKING NORTH; HOUSE MOUNTAIN IN THE BACKGROUND.
UUSSBLL.J RESIDUAL CLAYS IN CALIFORNIA. 27

of the southern Appalachians, so far as the conditions of transportation are concerned, the evidences of subaerial decay are not strongly 

pronounced, and, in fact, are usually absent. It is a matter of observation that the soil formed by the decay of a great variety of rocks is a 

red clay, which, in the more advanced stages of decomposition, is strikingly similar, both in appearance and in constituents, the world over. 

In the arid portion of the Far West soils of this character are wanting, and the prevailing tone of the landscape, so far as it is influenced 

by the color of the soil, or by the color of subaerial deposits generally, 

is subdued an.l unobtrusive, being usually gray, or light yellow brown. 

The brilliant coloring on the mountains and the gorgeous hues revealed 

in the canons of this region are not due to products of decay, but to 

the inherent tints of the rocks. The marked contrast that exists in the 

colors of the superficial deposits in the South Atlantic and South Pacific borders of the United States can be illustrated in fancy by comparing the ashen tints of the Mojave desert with the brilliant reds and 

yellows that would be revealed could the vegetation be removed from 

Virginia and her sister States.

In considering the absence of red soils in the Far West the arid region 

alone is referred to. There are areas of considerable extent on the west 

slopes of the Sierra Nevada where deep rock decay has taken place and 

where the red color of the soil reminds one of the southern Appalachians. 

In this region the present rain-fall is about forty-live inches annually, 

and the country is clothed with vegetation. The climatic conditions thus 

approximate to those prevailing in the Middle Atlantic States, and the 

decay observed in the rocks, including schists, slates, and limestones, 

is what one would expect from the climatic environment. The west 

slope of the Sierra Nevada in central California is a plane inclined at a 

. gentle angle, in which the streams have sunken their channels a thousand feet or more. The canons are narrow, with precipitous sides, 

and are floored with rock that has suffered but little decay. These 

conditions indicate that the region referred to underwent a long period 

of disintegration before the plain was tilted so as to allow the streams 

to excavate their present channels. That the stream channels are of 

more recent origin than the principal part of the rock decay is shown 

by the occurrence of residual clays, sometimes fifty or seventy-five feet 

thick, on the hill-tops. These conditions are well illustrated in the 

hydraulic mines oh Feather Eiver, and may be studied to advantage 

at Colfax, Cal.

There are probably other areas in the'Far West where rock decay is as 

marked as on the west slope of the Sierra Nevada^ but they have not 

come under my notice. What the effects of the heavy rain-fall, and consequently dense forests, of the northern part of the Pacific Slope may 

be on the decay of rocks remains to be observed.

(559)
28 SUBAERIAL DECAY OF ROCKS. [BULL. 52.

STJBAERIAL DECAY IN OTHER COUNTRIES.

The studies of previous observers have shown that subaerial decay 

is a marked feature of the surface rocks in many other countries.

The extent to which rock decay has reached in portions of Central 

America is indicated by the following quotation descriptive of portions 

of Nicaragua, by Thomas Belt: 1

The decomposition of the dolerites is very great, and extends from the top of the 

hills to a depth (as proved in the mines) of at least two hundred feet. Next the 

surface they are often as soft as alluvial clay, and may be cut with a spade. This 

decomposition of the rocks near the surface prevails in many parts of tropical America, and is principally, if not always, confined to the forest regions. It has been ascribed, and probably with reason, to the percolation through the rocks of rain water 

charged with a little acid from the decomposing vegetation. If this be so, the great 

depth to which it has reached tells of the immense antiquity of the forests.

On the island of Cura9ao, off the coast of Venezuela, as described by 

W. M. Gabb,2 the rock is limestone and the soil is scanty. ." There is 

no vegetable mold, and the ear^h is red, the same characteristic 'red 

earth' or clay as that found in Jamaica, Santo Domingo, the Bahamas, 

etc. The climate and vegetation are very similar to the rainless parts 

of Santo Domingo."

The observations of Agassiz, Liais, and Hartt indicate that the rocks 

over a large portion of Brazil have also been profoundly affected by the 

chemical action of the atmosphere and of atmospheric waters.3

In southeastern Europe a superficial deposit of red clay, or "terra 

rossa," resulting principally from the subaerial decay of limestone, occurs throughout tbe Istrian Peninsula, Dalmatia, Greece, etc. This 

deposit has been described and discussed to some extent by Stoppani, 

Fuchs, Neumayr, and others.

In the Spanish Peninsula the products of subaerial decay are to be 

seen on every hand; especially in the region southward of Madrid, 

where the landscape frequently calls to mind the characteristic features 

of central Virginia.

In southern Asia the deposit termed "laterite," formed by the subaerial decay of basalt, gneiss, granite, etc., is of wide geographic extent, 

and is one of the most interesting features in the surface geology of the 

country. Its thickness on the basaltic plateaus of western India sometimes reaches two hundred feet. Near Madras it imparts its characteristic color to the Eed Hills. When not exposed directly to the action 

of the atmosphere, it is soft and may be easily cut into blocks with a 

knife; on exposure to the air these soon harden sufficiently to form a 

durable building stone. This formation is so widely spread and so 

characteristic that it has attracted the attention of nearly all who have

J The Naturalist in Nicaragua, London, 1888, 12mo., p. 86.

2 Notes'on the Island of Curacao, Am. Jour. Sci., 3d series, vol. 5, 1873, p. 383.

3 For references consult bibliographic list at the end of this paper.

(560)
RUSSELL.] RED EARTH OF BERMUDA. 29

studied the geology of India. The observations concerning it have been 

summarized by Medlicott and Blanford in their Manual of the Geology 

of India.

The subaerial decomposition of basalt has been observed by J. D. 

Dana in Australia, Tahiti, and Tierra del Fuego; and similar alterations of other rocks have been noted in New Zealand and in China.

Perhaps the most instructive instance of the origin of a residuary deposit rich in iron from a formation that is not iron-stained is furnished 

by the " red earth " of Bermuda. The islands are composed,-probably 

throughout, of coral limestone and are remote from any region that 

could contribute foreign material in any considerable quantity. The 

soil is a red clay which has been left as the more soluble portions of the 

limestone were dissolved away. In composition it closely resembles the 

similar red soils of Virginia and of many other regions, as is shown by 

the following analyses which we copy from 0. Wyville Thomson's book, 

The Atlantic: 1

Analyses of red soil and of coral from Bermuda,

Constituents.

Lime(CaO) .... ..................

Chlorine (01).. ...................

Potash (K2 0)....-. ...............

Soda (Na2O). ............. ....'....

Phosphoric acid (estimated in niTotal ........................

Ked soil.

18. 265

45. 156

13. 898

15. 473

3.948

2.533

0.539

0. 133

0. (107

0.704

100. 656

Coral from 

which the rod 

soil wus derived.

0. 328

0.052

> 0. 540

54.496

44.521

0.214

0. 021

1. 751

0.066

0. 252

0.080

109 '#>1

An earth of similar character and origin occurs in the Bahamas, 

where the underlying rock is also coral limestone.

Superficial deposits resulting from secular decay have been described 

by various geologists in this country, as is indicated by the accompany-

'Vol. 1, pp. 325, 327. These analyses have been recalculated and organic matter 

left out. Other analyses of the soils of Bermuda may be found in J. H. Lefroy's 

essay on the botany of Bermuda, Bull. U. S. Nat. Mus. No. 25.

(561)
30 SUBAERIAL DECAY OF ROCKS. [uuLL.52.

ing bibliographic list: but these observations are not inserted here at 

length, as they have already been assembled by T. Sterry Hunt in his 

essay oil the decay of rocks. 1

CONDITIONS FAVORING THE DECAY OF ROCKS.

The extent below the surface to which rock decay extends indicates, 

iu addition to the evidence of chemical changes, that such alterations 

have been produced by percolating waters and not by changes of temperature or any other cause with which ,we are familiar. The strain 

produced by changes of temperature and the freezing of water in the 

interstices of rocks, although of very great importance in assisting in 

their alteration, is confined to the superficial portions of outcrops.

The conditions, therefore, which facilitate the passage of percolating 

waters, especially of waters charged with organic acids through rocks, 

will favor decay. As is shown below, this process is regulated by cli. 

mate.

In desert regions a hard, superficial crust is frequently formed on 

rock surfaces, probably by the deposition of mineral matter brought in 

solution from the inner portions of the rocks and precipitated as evaporation takes place. The " desert varnish,-" so common in arid regions, 

appears also to be of this nature. When the climate is sufficiently dry 

to admit of the formation of incrustations of this character, atmos-. 

pheric influences are evidently conservative rather than destructive.

In high latitudes very little evidence of subaerial decay has been 

noted, but this may be due to lack of observation, to the recent existence of glaciers, or perhaps to the prevalence of abundant means of 

transportation.

I.may remark from observation that in the Kerguelen and Crozet 

Islands, in the South Indian Ocean, where a cold, humid climate prevails, and where not Only forests but arborescent growths of every description are wanting, there is but little soil, and nothing approaching 

terra rossa is to be seen. These islands are formed, probably throughout, of dark basaltic rocks, rich in iron, which under more favorable 

conditions would yield a deep layer of ferruginous soil. Contrast with 

the Kerguelen Islands others of similar origin in the tropics, as the 

Samoan Islands, for example. On Kerguelen the highest vegetation is a 

bitter cabbage which grows mostly in sheltered places along the coast, 

where it is surrounded with matted ferns and tussocks of moss. The 

landscape, even on the exceptional days of sunshine, is dark, silent, 

arid gloomy. Among navigators this island is called, not unjustly, the 

" Land of Desolation." In the Samoan Islands the rank luxuriance of 

tropical vegetation imparts to the. laud when seen from the ocean the 

deep tint of malachite. Wherever the bare earth appears it gleams

J Aiu. Jour. Sci., 3d series, vol. 26,1883, pp. 190-213. Republished in Mineral Phys* 

iology and Physiography, Boston, 1886, pp. 246-278.

(562)
RUBEUCLL.I CLIMATE AND ROCK DECAY. 31

forth through the overshadowing boughs with a brilliancy that is enhanced by contrast and gives a dash of Pompeian red to the picture of 

tropical beauty. The soil is deep and rich, and, as in Bermuda, must 

have been derived entirely from the decay of the rocks forming the 

islands, which in this case, however, are basaltic, and agree in many 

ways with the rocks forming the Kerguelen Islands.

The contrast between the present condition of the Kerguelen Islamls 

and that of the Samoau Islands has resulted from differences in climatic conditions. This conclusion would have to be modified, perhaps, should it be found that the former had recently been glaciated. 

There are abundant observations to show, however, that, in general, 

islands below latitude 50° south, where winter is almost continuous, 

are desolate, uninhabitable wilds, and that forty degrees nearer the 

equator, where perpetual summer reigns, lands formed of nearly identical rock have suffered deep decay and are covered with a rich ferruginous soil, which supports a varied and luxuriant tropical flora.

These observations concur with the conclusions of G. P. Wall and 

J. G. Sawkins concerning the formations of the soil of Trinidad, from 

which the following is copied: 1

When the temperature is low, as in northern climates, the operation [of rock disintegration] (notwithstanding the action of frost) progresses very slowly. The soil, is of 

the thinnest description, and even a bare surface of the original rock is frequently 

.exposed; but, under this latitude [ten degrees north] and with the excessive moisture of this climate, it may be doubted whether any but the hardest quartz can entirely 

escape degradation, while in most cases the resulting soil will be of great depth.

On considering the geographical distribution of residual deposits, together with other facts bearing on the question, it seems safe to conclude that, in general, subaerial decay is more rapid in warm than in 

cold regions, and is far greater in humid than in arid climates. The 

most favorable conditions occur in warm, moist climates.

The intimate relation between climatic conditions and rock decay 

here stated might perhaps be considered a.s simply a coincidence, and 

not of the nature of cause and effect. The writer is not prepared to 

discuss in all their details the chemical processes which have transformed the superficial portions of the earth's crust and rendered it suitable for the formation of soil and the growth of vegetation, but the effects of climate in this connection may be designated in a general way.

Among the first conditions influencing rock decay is temperature. 

Its direct effects are felt in two ways: (1) The warm waters of temperate and tropical climates have greater solvent power than the colder 

waters of higher latitudes; (2) in warm regions the surface waters are 

enabled to exert their influence throughout the year, whereas in colder 

climates the ground is frozen during a portion of the year at least, the 

percolating of surface water is checked, and its chemical effects are 

decreased. More than this, precipitation is, in general, greater in low

t Kept, ou the Geol. of Trinidad, London, 1860, p. 70. 

(563)
32 SUBAERIAL DECAY OF KOCKS. [BULL. 52.

than in high latitudes, and takes the form of warm rain which saturates the ground instead of falling in great part as snow. Genial temperatures and abundant rain-fall are accompanied by luxuriant vegetatiou, which not only retains rain-water at the surface and allows it to 

percolate slowly downward, but imparts to it various organic acids, 

thus increasing its solvent power. The tendency of all these conditions 

is to produce greater chemical alterations in the rocks of warm, moist 

regions than in those of cold countries. As the regions of abundant 

rain-fall and rank vegetation pass by insensible gradations into cold or 

arid, barren regions, so the products of rock decay change by insensible gradations from regions like the southern Appalachians, where they 

reach a maximum, to other areas where they are for the most part 

wanting.

The intimate connection between existing climatic conditions and 

rock decay has been clearly recognized by F. von Eichthofen, 1 who 

states that 

Weathering, in fact, becomes in large measure a climatic phenomenon. In moist 

and hot regions it is accomplished easily and rapidly; in hot and dry regions it 

seems to play an unimportant part, and where high degrees of cold prevail even an 

abundance of water is unable to produce it in any but an insignificant amount. Beneath the ever moist moss cushions of Finland and the northern Ural, granite shows 

undecomposed surfaces.

The conclusions presented above are quite the reverse of those arrived 

at by certain writers who have previously considered the subaerial 

decay of rocks. Thus, Th. Fuchs, in his essay entitled, "Zur Bildung 

der Terra rossa," iu which the origin of the terra rossa, or Karst earth, 

of southeastern Europe is considered, says:

One can hardly avoid the thought that the presence or absence of terra rossa is 

essentially dependent on climatic conditions; that it appears only where a dry climate prevails, and hence vegetable growth is scanty, whilst it can not appear where 

there is a m,oist climate, luxuriant vegetation, and consequently a greater accumulation of humus substances produced by both causes.

The greater extent of subaerial rock decay iu the Southern than in the 

Northern States has been forcibly stated by W. 0. Stnbbs,2 in reference 

to the formation of soils from the crystalline rocks of the southern 

Appalachian region, as shown in the following quotation :

* * * Decomposition of these rocks in southern latitudes has proceeded much 

farther than with same rocks in higher latitudes, and therefore has given us deeper 

soils. It is difficult to find in the North a soil over a few feet deep, while here it is 

not uncommon to find in railroad cuts, wells, etc., disintegrated strata to the depth 

of thirty, fifty, or even seventy-five feet. This can be accounted for to a large extent 

by climatic influences. The warm waters, charged with carbon dioxide, percolating 

throughout the year the easily permeable strata, act continuously as a chemical agent 

iu the work of disintegration ; while farther north not only the amount of water, the 

temperature, and the chemical activity are reduced, but for one-half of the year the 

soil is locked up by frost from all access of decomposing agencies.

1 Fiihrer fiir Forschuugsreisende, Berlin, 1886, p. 100.

2 The soils of Alabama, in Benney's Hand-book of Alabama, Mobile, 1878, p. 199.

(564)
RUBSBLL.] CLIMATE AND ROCK DECAY. 33

The conclusions expressed in the above quotation have been cited 

with approval by F. H. Storer 1 in a note on rock disintegration in hot, 

moist climates. Very decided exception to these views has been taken 

by T. Sterry Hunt,2 however, who insists that "present climatic differences have nothing to do with the fact that similar rocks are in one area 

covered with the products of decay and in another are wholly destitute 

of it." Hunt calls attention to instructive instances (some of which apparently admit of other interpretations) where ancient land surfaces 

have been protected beneath later formations, showing that subaerial 

decay took place during past geologic ages. He also points out that 

the rocks of the inetamorphic portion of the Appalachian region have 

been exposed to atmospheric influences for a very great length of time. 

The high antiquity of the residual clays of the Southern States is 

discussed in an earlier article by the same author,3 in which the opinion is expressed that the chemical decomposition of the. rocks referred 

to was "effected at a time when a highly carbonated atmosphere aud 

a climate very different from our own prevailed."

The assertion that the accumulation of the residual clays now forming the surface of our country over thousands of square miles took 

place when the climate and the composition of the atmosphere wrre 

very different from what they are at present, carries back the origin of 

these deposits to an age geologically so remote, that it antedates the 

very origin of the rocks from which the residual clays were derived. 

It may be asked what was the time a when a. highly carbonated atmosphere and a climate very different from our own prevailed ? " Certainly not in the Tertiary, for our country w;is then clothed with forests closely resembling those now growing, and inhabited by land 

animals in great numbers that could wot have differed markedly in their 

habits of life from existing mammals. These same arguments apply, 

less positively, to the Cretaceous, Jurassic, and Triassic periods. It is 

believed by certain geologists that the luxuriant Carboniferous forests flourished in fin atmosphere more highly charged with Carbonic 

acid than at present. It seems, therefore, that the " great antiquity" 

of the residual clays claimed by Hunt must refer to the Carboniferous 

or to pre-C'.irboniferous ages; that is, to a time preceding the deposition of the rocks of the Newark system, and antedating the upheaval 

of the strata in which the Great Appalachian Valley has been eroded.

Still further evidence bearing on this question is furnished by the 

red earths of Bermuda, Santo Domingo, Trinidad, Jamaica, etc., which 

have resulted from the decay of Tertiary or post-Tertiary limestones.

1 Science, vol. 1,1883, p. 39.

2 The decay of voqks geologically considered; in Am. Jour. Sci., 3d series, vol.25, 

18S3, pp. 190-213.

3 Proo. Boston Soo. Nat. Hist,, vol. 16, 1873-74, pp. 115-117. See also "The disintegration of rocks ;md its geological significance," by tlie gauie author, Proc, Aw, 

A-saoc. £dv. Soi,, 23d (Hartford) meeting, 1875, pp, 39-41,

Bull, 52 3 (565)
34 SUBAERIAL DECAY OF EOCKS. [HULL. 52.

It must be admitted by every geologist that a chemical alteration of 

surface rocks has been in progress from the first appearance of laud on 

ihce.arth to the present day, and may have beeu more active in past ages 

than now. Denudation lias accompanied decay, however, and the residual deposits now remaining represent the net excess of disintegration 

and decomposition over transportation. In no region of any considerable extent is denudation so limited that the residual deposits formed 

during past geological ages can be expected to have withstood denudalio.u and to have remained intact to the present time, unless they have 

been protected by subsequent deposits, preserved in caves, or otherwise 

sheltered. We must conclude, therefore, that such deposits now found 

at the surface throughout the southern Appalachian region have been 

formed during comparatively recent geologic times and that their 

accumulation is still continuing. This conclusion is enforced by the 

fact tha.t many thousands of feet of rock have been removed from large 

portions of the Appalachian belt since the elevation of the mountains, 

and that hundreds and probably thousands of feet of strata have been 

eroded from the Atlantic border since the upheaval of the rocks of the 

Newark system.

The observed increase in the decay of the rocks as oue travels southward along the unglaciated portion of the Appalachian region, and the 

occurrence of characteristic residual clays on the west slope of the 

Sierra Nevada, where a comparatively moist climate prevails, certainly 

seem to indicate that rock disintegration and decay are intimately related to the humidity and the temperature of the present climate. Before this conclusion is accepted, however, another hypothesis should 

receive attention.

EFFECTS OF GEOLOGICALLY RECENT GEOGRAPHIC MOVEMENTS ON 

THE DISTRIBUTION OF THE RESIDUAL DEPOSITS OF THE APPALACHIAN REGION.

Throughout the Appalachian region traversed by mo in 1885, 1S8G, 

and 1887 the streams flow over rocky beds and are broken here and 

there by cascades, caused by layers of rocks harder or more insoluble than their neighbors, as illustrated by Plates IV and V. The 

fact that the streams flow over rocky beds has been observed throughout the Appalachians and the adjacent Piedmont region from Pennsylvania southward, and at many localities in the northern part of the 

same belt as well. It is apparently safe to say that the Appalachian 

streams at the present time are deepening their channels. In other 

words, the present drainage has not reached a base level of erosion, 

and has probably been affected by a comparatively recent change in 

the level of the land, which has caused a renewal or a continuation of 

corrasion. This change must have been comparatively recent, for the 

 reason that if the land, had been stable fora Iqug time, geologically

(566)
U. S. GEOLOGICAL SURVEY BULLETIN NO. 52 PL, IV

MAYO RIVER. NORTH CAROLINA, ILLUSTRATING THE MANNER IN WHICH THE RIVERS OF THE 

PIEDMONT REGION ARE ERODING THEIR BEDS.

The rocks producing the rapids are Newark sandstones.
.] ItECENT ELEVATIONS IN THE APPALACHIAN REGION. 35

speaking, the streams would have reached the limit to which they could 

deepen their channels ami would be iVee from falls. This statement 

applies, however, only to that portion of the Appalachian belt where 

the drainage has not been affected by glaciers. Exception is also made 

of localities like Lookout Mountain, which have been left in relief by 

the more rapid denudations of surrounding areas. The fact that many 

of the Appalachian streams are flowing through narrow canons, instead 

of broad valleys, likewise indicates that a base level of erosion has not 

been reached.

In reference to the rate at which the streams are now deepening their 

channels, there is apparently little if any difference in the various portions of the Appalachian belt. A critical examination might perhaps 

show, however, that the streams at the North are cutting more rapidly 

than those at the South, and that the change from north to south is

gradual. As will be seen a little later,.this would be in harmony with 

the evidence that a recent elevation of the northern part of the Appalachians lias taken place.

When we consider the terraces bordering the present streams, which 

record former changes in the level of the land, a marked difference is 

at once apparent between the extreme portions of the Appalachian 

belt. The stream valleys at the north are terraced. In the central 

portion of the region the terraces are fewer and more obscure than at 

the north. Southward, below the James, for example, terraces are 

wanting, or if occasionally seen they are obscure and difficult to distinguish. The.presence of stream terraces at the north and their absence 

at the south indicate that there has been a recent elevation of the 

northern portion of the Appalachian belt.

An increase in elevation of a large area would be followed by more 

rapid stream erosion, consequent on increased declivity, among the first 

effects of which would be the removal of residual deposits from all regions having free drainage. The comparatively recent elevation of the 

land indicated by the terraces along the streams north of the James 

may therefore account, at least in part, for the scarcity of residual clays 

in the central and northern portions of the Appalachian belt.

If we assume that a sheet of residual clays of uniform thickness covered the Atlantic States previous to the Glacial Epoch, the present unequal distribution, disregarding for the moment climatic influences, 

may be referred in part to each of two causes: First, the removal of the 

residual deposits from the region occupied by ice through glacial action. That this would be the result of the advance of a vast ice sheet is 

conceded by every one who has investigated the question, and need not 

claim further attention at this time. Second, the thickening of the 

sheet of residual clay toward the south from the southern margin of the 

glaciated area would be due to unequal erosion produced by unequal 

upheaval of the Appalachian region.

(567)
36 SUBAERIAL DECAY OF ROCKS. [BULL.52.

The effects of climate and of upheaval on residual deposits thus furnish two hypotheses to account for the observed increase in thickness 

of the products of decay as one travels southward along the unglaciated 

portion of the Appalachian belt. These may be called:' (1) the hypothesis of climatic variation; (2) the hypothesis of orographic movement.

The coi rect explanation of the facts observed in reference to the present 

distribution of residual deposits in the region under discussion probably lies in part in each of these hypotheses.

In a belt of country extending more than a thousand miles from north 

to south and composed from end to end of similar rocks, as in the case 

in the Appalachian belt, it is safe to assume, in view of the facts already presented, that weathering will be unequal, owing to variations 

of climate. In the case before us, however, the conditions have been 

varied by oscillations of the land at a late date in the period of decay, 

which have accelerated denudation over the northerh portion of the belt.

My conclusion from the facts already presented, together with the 

impressions received in the field, but difficult to formulate, is that each 

of the causes mentioned above has had its share in producing the observed differences in the distribution of the residual deposits throughout the middle and southern portions of the Appalachian region, but 

that the controlling influences were temperature and humidity.

Jt is not to be inferred from what has been said in the preceding passages that no decay has taken place in the rocks of the Northern States. 

On the contrary, wo have evidence, especially in the driitless area of 

the Upper Mississippi Valley, that the rocks at the North were disintegrated to a considerable depth before the advent of the great ice 

sheet; but, judging from the condition of the unglaciated area, this 

change was not nearly so pronounced as at the South. The ice erosion 

of the Glacial Epoch not only removed and commingled the previousl}7" 

formed residual deposits, but planed away the country over a vast area 

to a greater depth than had been reached by the previous decay. 

This is shown by the freshness of the rocks on glaciated surfaces and 

by the solidity of many of the bowlders composing the moraines left by 

the ice.'

The conclusion that snbaerial decay is intimately related to existing 

climatic conditions does not appear to hold in Southeastern Europe and 

in.portions of India, where, it is reported, extensive residual deposits 

occur in connection with comparatively dry climates. Very recent 

changes in the humidity of these regions may have occurred, however, 

which would remove the objections presented by their present condition.

The diversity of opinion indicated by the citations given above encourages a hope that the subject treated in this paper in;iy receive 

greater attention from geologists, and that observations; may bo multi-

(568)
U. S. GEOLOGICAL SURVEY

VIEW FROM HARPER'S FERRY, WEST VIRGINIA, LOOKING DOWN THE POTOMAC.
RUSSELL-.] ANALYSIS OF JAMES EIVER WATER. 37

plied with reference especially to the geographic distribution of residual 

deposits and to the chemical changes that they have undergone. The 

mechanical condition of residual deposits is also worthy of attention, 

for the reasou'that the decay of rocks furnishes the raw material, so to 

speak, .for the formation of sedimentary strata, and a knowledge of its 

characteristics will assist geologists in determining the nature of the 

parent rocks from which ancient clastic beds were derived.

THE SOLUBLE PORTIONS OF ROCKS.

I have approached the study of the chemical alteration of rocks by 

examining the deposits remaining after rocks have been exposed to a 

mild solvent, i. e., ordinary surface water, for a great length of time. 

The investigation might have been commenced by studying the soluble instead of the insoluble portions of rocks; in fact this is the 

usual method, as is shown by the many essays already written on the 

chemistry of natural waters. The problem is concerned mainly with 

solubility combined with oxidation. The mineral matter dissolved in 

rivijr waters represents the soluble, and. residual deposits represent the 

insoluble portions of rocks. It is evident that the average composition 

of the residual deposits of a given region should be the complement of 

the mineral matter contained in the streams flowing through it. Together these should represent the average composition of the rocks of 

the area in question..

It is not my aim to undertake the study of the chemistry of natural 

waters this has already been done by able chemists; but it is of interest, in connection with an examination of residual deposits, to know 

what mineral substances are commonly contained in river waters. For 

this purpose the following analysis of the water of the James Eiver,1 

Virginia, which drains a region covered throughout with residual deposits, is inserted. The sample analyzed was collected at Kichmond, 

October 24, 1876, after a light rain.

'Analysis reduced to parks per thousand. From Annual Report of the Richmond 

[Va.] Board of Health for 1876. See also Geological History of Lake Lahoutau, MOD. 

U,. S. Geol. Survey, No. 11, pp. 17:5, 174.

(569)
38 SUBAEK1AL DECAY OF ROCKS. [HULL. 52.

Analysis of Ike water of James Iliver, Virginia. By W. 

H. Taylor.

Constituents.

Sodium (Na) .........................

Potassium (K).......................

Calcium (Ca) .......................

Magnesium (Mg) .....................

Chlorine (Ul)...... ...... ...... .......

Carbonic acid (CO...).................

Sulphuric acid (S03 ) ................

.Phosphoric acid (HPO;! )..............

Nitric acid (N0r.) ....................

Silica (SiOi)-------------.--..-.-....

Alninina (Al.2 0n)......................

Sesqnioxidcs of iron (FojOu)..........

Sesqnioxidos of manganese (Mn 2 0:{ ).. 

Ammonia (NH4 ) ......................

Organic matter .......................

Total

Parts per 

thousand.

.00244

.00251

,01284

,00377

.00105

.02954 

.00363 

trace 

,00231 

.01024 

,00041

,00072

,00001

,00299

,07246

From the analysis of the waters of twenty American rivers it has 

been ascertained that the average of solids in solution is 0.15044, and 

the average of calcium carbonate 0.05G416 part per thousand. 1 The 

average of total solids in solution, as derived from a table of forty-eight 

analyses of European river waters given by Bischof,2* is 0.2127, and 

the average of calcium carbonate 0.1139 part per thousand.

The analyses of thirty-six European river waters, published by Roth,3 

including some of those tabulated by Biscliof, give 0.2033 part per 

thousand as the average of total solids and 0.09508 part per thousand as the average of the calcium carbonate. ]n both American 

and European river waters, so far as can be ascertained from the data 

in hand, the average of total solids in solution is 0.1888 and the average 

of calcium carbonate 0.088765 part per thousand. In a general way, 

therefore, the amount of calcium carbonate dissolved by river waters 

may be taken as about one-half the amount of total solids in solution.

The amounts given above seem insignificant when considered by 

themselves, but when we remember the vast volume of water discharged 

by rivers every day, the quantity of solids in solution thus transferred 

from the land to the sea is seen to be so great, even in a single year,

'Geol. Hist. Lake Lahoutau, Mon. U. S. Geol. Survey, No. 11, pp. 173,174. 

2 Chemical Geology, English edition, London, 1854, vol. 1, pp. 76,77. 

3 Chemical Geology, vol. 1, Berlin, 1879, pp. 450, 457.

(570)
BUBBKLL.J MINERAL MATTER IN SOLUTION. 39

that we are uuable to comprehend the meaning of the figures that indicate its magnitude.

For example, it has been estimated that the Thames, England, carries daily 1,682 tons of inorganic matter in solution, of wliich 1,121. tons 

are calcium carbonate. The Croton, New York, carries daily 183 tons 

of inorganic matter in solution, of which 47 tons are calcium carbonate; 

the Hudson, New York, 4,000 tons, of which 1,200 tons are calcium carbonate; the Mississippi 309,100 tons, of which 137,419 tons are calcium 

carbonate. The Mississippi alone carries annually nearly. 113,000,000 

tons of mineral matter in solution in addition to its visible load of silt 

carried in suspension, which is about four times as great. 1

From another analysis T. Millard Eeade'J has computed that the Mississippi discharges annually 150,000,000 tons of solids in solution. As 

this computation an'd : the one presented above are each'based on a 

single analysis, the discrepancy in the results reached is not remarkable.

Computations of this nature might be multiplied indefinitely, but the 

brief statements already given are sufficient to show what becomes of 

the vast quantity of soluble matter removed from the land in connection 

with the formation of the residual deposits which impart their characteristic color to large portions of the earth's surface.

CHARACTERISTICS OF RESTDUAL CLAYS.

A few chemical analyses of residual clays have been given in the preceding pages in connection with descriptions of the decay of rocks at 

various localities, but it is of interest to assemble these and other analyses of a similar character in a tabular form, in order to show especially 

the close similarity that exists in the composition of residual deposits 

of various countries, even when derived from rocks which differ widely 

in both chemical and physical properties.

In the following table, the analyses numbered 1, 2, 3, and 7 have been 

given in the preceding portion of this paper. No. 1 shows the composition of a red clay derived, as nearly as can be determined, from chloritic 

schist. No. 2 is an analysis of decomposed trap (dolerite) from the 

Newark rocks at \ATadesborough, N. 0. No. 3 gives the composition of 

dark red residual clay derived from Trenton limestone near Lexington,Ya. No. 4 shows the average composition of four samples of residual clay formed by the decay of limestone in the driftless area of 

Wisconsin.3 No. 5 is the analysis of a kaolin, now used in the manufacture of pottery, from Chestnut Hill, Lancaster County, Pa. This is 

also a residual clay, and is considered by J. P. Lesley as having been

Tor references, see Geol. Hist. Lake Lahontau, Mon. U. S.'Geol. Survey, No. 11, 

pp. 174, 175.

-Denudation of the two Ai.neri.cas. Presidential address; Proc. Liverpool Gcol. 

Soc., vol. 5, 1S84-'S5, pp. 8-45,

3 Publislied by ChaniberUn and Salisbury, in tlio Sixth Ann. Kept. U. S. Geol. Survey, 

p. 250.

(571)
40 SUBAER1AI, DECAY OF ROCKS.

derived from " potash (orthoclase) feldspar rock." . The analysis is by 

F. H. Genth. 1 No. 6 is the analysis of u typical kaolin or china clay, 2 

the composition of which may be represented thus: 2SiO2 , Al2 0:i, 2H2O. 

No. 7 a red clay derived from the decay of Knox dolomite, Morrisville, 

Ala.

Analyses of residual clays.

SiOa .............

A1203 ............

Fe,03 ... .........

FeO .............

HaO .............

MnO.. ...........

CaO .............

MgO. ............

Cr2O3 ............

Na2O ............

K20 ....... ......

PsOa- ......... 

TiOa. ............

C02 .... ..........

c... .............

Total .......

No. 1.

54.54

26.43

9.04

9.87

(J9. 83

No. 2.

39.55

28.76

16.80

13.26

0.37

.0.59

Trace,

rPrn PO

0.10

0. 64

100. 07

No. 3.

43.37

25.07

15.16

12.98

0.63

0. 03

1.20

2.50

100.94

No. 4.

55. 73

18. 16

10.57

0.63

«9.40

0.03

O.i?9

. 1.12

1. 44

1 24

0.03

0.26

0.35

0.46

100. 41

No. 5.

67.1

20.1

3.9

' rt 0

0.1

0.7

2.0

99 8

No. 6.

46. 33

39. 77

13.90

100. 00

No. 7.

55.42

22 17

8.30

9.86

0.15

1.45

0.17

2.32

Trace.

99. 84

a Contains H of organic matter.

This table might be increased almost indefinitely, if so desirecl, by 

consulting reports on agricultural geology and other similar treatises. 

In Eugene A. Smith's report on the Agricultural Features of Alabama,3 

especially, there are numerous analyses of soils formed of residual clays, 

which agree very closely iu chemical composition aud physical characters with the examples presented above.

In the analyses given in the table, it will be noticed that silica, alumina, 

ferric oxide, and water make up over 90 per cent, of the residual clays 

examined. As the samples analyzed are typical of their class aud agree 

essentially with many other analyses of a similar character with which 

they have been compared, we may conclude that residual clays in general are ferruginous kaolins of varying degrees of purity. They differ 

from ordinary brick-clays since they have resumed from chemical decomposition and not from mechanical disintegration. They are hydrous 

and have a very low percentage of soluble salts; in both of these par1 Annual Rept. Geol. Survey Pennsylvania for 1885. p. 588. 

2A. H. Green's Physical Geology, 3d ed., London, 18S2, p. 174. 

3In Geol. Survey Alabama, Rept. for the years 1881 and 1882.

(572)
UU6SKLL.J COLORS OP RESIDUAL CLAYS. 41

ticulars they differ from clays produced by mechanical means. The 

line sediment deposited by many glacial streams is remarkably claylike in its physical properties, but chemically it has essentially the 

same composition as the rocks from which it was derived. The differences between glacial and residual clays have been clearly stated by 

Chamberlin and Salisbury in their description of the unglaciated areas 

of the Upper Mississippi Valley, previously referred to.

The close similarity between the analyses of residual clays from various localities and from diverse geologic formations, indicated in the 

table, is found only when the chemical decomposition, or decay, is far 

advanced; otherwise the residual material may contain fragments of 

undecomposed rock. Under the microscope a typical residual clay 

should show only amorphous matter, free from particles of crystals and 

rock fragments. In the examination of a large number of samples this

complete disintegration was seldom seen, however, as the clays nearly

always contain quartz fragments and not infrequently particles of other 

minerals.

In color, residual clays are usually red, owing to the oxidation of the 

iron contained in the minerals composing the original rock; but in some, 

cases they are mottled red and yellow, or may have various shades of 

yellow, brown, purple, etc. It is the characteristic red color which 

gives the name terra rossa to the residual clays of Southern Europe. 

Un weathered clastic rocks, on the other hand, are usually gray, green, 

blue, etc., but are seldom red. All who traverse the Great Appalachian 

Valley or th« Piedmont region of Virginia, the Carolines, Georgia, and 

Alabama, must be impressed by the charming bits of color imparted to 

the landscapes by the red clays of the roads and fields. In dry weather 

this material is-nsually compact and hard, forming excellent roads,but 

(luring the rainy season the highways become soft and almost impassable. Among the many differences to be seen between a glaciated country, like New York and the New England States, and a region in which 

atmospheric decay has progressed uninterruptedly for geologic ages 

the colors of the soil and the prevailing tints of the landscape are not 

the least conspicuous. In glaciated regions the landscape is mostly 

sombre, usually gray, when not covered with vegetation, excepting 

where the rocks themselves are red, as in the Newark areas of New 

Jersey and the Connecticut Valley. But on an old land surface, where 

decomposition is far advanced, brilliant dyes are to be seen wherever 

the turf is broken. Although the rich color of terra rossa is especially 

pleasing to those who are sensitive to the play of tints in a landscape, 

yet at times it serves only to increase the ugliness of unsightly cuts and 

embankments. In such instances it seems as.if the earth bled from 

the wounds inflicted by man.

The contrast in color between northern and southern landscapes in 

the Appalachian belt has recently been explained by W. O. Orosby, in

(573)
42 SUBAERIAL DECAi" OF ROCKS. IHULL. 52.

aii essay on the colors of soils, 1 on the assumption that the observed 

difference of color has resulted directly from differences of temperature 

between ihe North and the South. In the essay referred to it is urged 

that the higher temperature at the South is capable of dehydrating the 

ferric oxides impregnating the soils, thus changing their color from yellow to red; and also that the red color of residual clays is a superficial 

phenomenon, confined to the immediate surface of the deposits.2 My 

own observations do not confirm these conclusions. At many localities in the Appalachian region south of Pennsylvania where residual 

deposits were observed, the characteristic red color was seen to extend 

far below the surface, and as a rule to reach the bottom of fresh exposures. In many localities the color of the residual clays at a depth 

of 20 or even 50 feet is similar, so far as Ihe eye can distinguish, to 

the color in the same sections only a Coot or two below the surface. The 

great depth to which the red color extends renders it evident that it 

can not be directly dependent on solar heat. Again, over considerable 

areas in the South the surface clays are various shades of yellow, which 

would not be expected if the red color of adjacent fields is due to temperature.

Moreover, the dehydration of ferric oxide, as stated by Crosby, takes 

place at a certaiu temperature (about that of boiling water in laboratory experiment), but is not considered as resulting from a high mean 

annual temperature. Under this hypothesis we must consider, therefore, that the heating of the earth during the summer months is sufficiently high in the Southern States to dehydrate ferric oxide, and that 

at the North this is not the case. Certainly a very delicate adjustment 

of chemical conditions is here postulated. Having experienced the 

summer's heat Doth at the North and at (he South, it seems to me 

.to be doubtful whether the soil in northern Alabama, for example, is 

more highly heated during the summer than the soil in Pennsylvania

and New Jersey. Exact observations on this point are not at linud.

The description of the colors of the residual clays in the metaruorphic 

region of Alabama, quoted on pages 18-20, should be read in connection with the discussion here referred to.

'Proc. Boston Soc. Nat. Hist., vol. 23, 1875, pp. 219-222. ...

2 This hypothesis has been applied by its author in an article on the "Geology of 

the Black Hills of Dakota" (Proc. Boston Soc. Nat. Hist., vol. 23, p. 500) in explaining the origin of the color of the Red Beds of othe Rocky Mountain region which it is 

claimed " depend [for their color] largely upon an excessively hot and dry climate ; 

and in the repeated exposures of the Red Bed sediments during their deposition to a 

hot and arid atmosphere." In opposition to this argument attention may be directed to 

the pi ay a-lake deposits of Nevada and Arizona which-are now forming'under the atmospheric conditions named above, but which are always creamy white in color. 

The temperature to which these beds are exposed during the summer months very 

commonly ranges from 110° to 120° Fahr. in the shade far exceeding any temperature reached in the southern Atlantic States.

(5.74)
OEES IN RESIDUAL DEPOSITS. . 43

ECONOMIC PRODUCTS OF EESIDUAL CLAYS.

The most important economic products of the residual clays in the 

southern Appalachian region is the iron ore they contain. This is often 

scattered irregularly through the terra rossa in concretionary masses 

varying from a small fraction of an inch up to a foot or more in diameter, .which frequently have a glossy surface and bear a somewhat close 

resemblance superficially to certain meteorites. At' other times the 

limouite is in irregular tubular masses of many tons weight. In both 

instances there is abundant evidence that the ore was deposited during the accumulation of the-residual clays in which it occurs. Several 

of the iron furnaces of Alabama and Georgia are supplied from ore of 

the nature described. Manganese ores of varying degrees of purity are 

also an accompaniment of residual clays of the Southern Appalachian 

region.

In a few localities in the region underlaid by the Lower Silurian 

rocks of the Great Appalachian Valley the residual clays contain baryte 

in considerable quantities. In these instances the baryte is.a residual 

deposit, having been left as the limestone in which it was originally 

formed was removed in solution. The red soil derived from the decay 

of this same limestone sometimes carries irregular fragments of galena, 

which formerly filled cavities of which tliey Nretain the form, and, like 

the baryte, they were left when the more soluble portion of their matrix 

was removed. The occurrence of gold in residual clays has already 

been referred to-. At some localities terra rossa has been utilized in the 

manufacture of bricks.

(575)
44 SUBAERIAL DECAY OF EOCKS. ' [BULL. 52.

II. ORIGIN OF THE RED COLOR OF CERTAIN FORMATIONS. 

A HYPOTHESIS PROPOSED.

It follows as a corollary from what has been said in a preceding portion of this paper that the iron-stained sands resulting from the subaerial 

decay'of crystalline rocks will furnish the material for red sandstones 

and shales when deposited in basins holding water. Exceptions may 

occur when the debris is subjected to sufficient attrition to remove the 

incrustations of ferric oxide or exposed to the action of chemical agents 

having the power to dissolve it.

It is well known that the red and brown colors of the Newark sandstone, and of many other similar sandstones and shales, are due to incrustations of ferric oxide which coat the surfaces of the grains of quartz 

and feldspar forming the strata and cement them together. 1

In order to verify the conclusions of previous observers in connection 

with this subject an examination was made of thirty thin sections of 

sandstone collected by the agents of the Tenth Census from quarries at 

various localities in the Newark areas from Massachuseits to North 

Carolina. All of the specimens examined were composed principally 

of angular quartz grains, with which were frequently mingled fragments 

of feldspar, hornblende, mica, etc. In several examples the rocks were 

gray, and derived their color from the inherent tints of the fragments 

composing them. In most instances, however, they had the brownish 

red color characteristic of the Newark system in general, and under 

the microscope revealed the fact that their color was not inherent in 

the particles composing them, but was due to a fine, amorphous, claylike coating which enveloped the grains and filled the interveningspaces. The edges of the quartz grains, as seen in thin sections, are 

sharply defined by a red line, the outer border of which is less definite 

than that next the .grains, and merges with the lighter red material filling the interspaces. The coloring matter which adheres to the grains 

is not composed of concentric layers, and does not show a crystalline 

structure facts which indicate that it was not deposited from solution. 

The rifts and crevices in the quartz grains are filled with material of 

the same character as that which stains their surfaces, and was evidently introduced from the outside.

That the characteristic color of these sandstones is due to material

'The appearance of a thin section of these sandstones when examined with a mi. 

croscopc has been described and illustrated by G. W. Hawes, Geol.New Hampshire, 

vol. 3, 1878, part 10, p. 240, Plate XII, Fig. G.

(576)
KL-ssiaM ORIGIN OF THE COLOK OF NEWARK SANDSTONES. 45

r.o.iting the grains of which they are composed, and filling the spaces 

between them, may also be shown by digesting the rocks in acids, when 

the color disappears and leaves the sands with their normal tints.

The-coloring matter of the Newark sandstones thus agrees with the 

coloring 'matter of residual deposits resulting from the subaerial decay 

of crystalline, rocks not only chemically, but also in the manner in which 

it iucrusts the grains.

We know that the debris composing the stratified rocks of the Newark system was derived from the waste of the surrounding crystalline 

areas. It therefore seems safe to conclude, especially when we consider 

the nature of the subaerial deposits now being produced by the decay 

of the crystalline rocks of the southern Appalachians, that the material 

composing them acquired its red color during the disintegration of the 

rocks from which it was derived. The red cementing material is residual clay or terra rossa,

If the hypothesis here advanced in reference to the origin of the red 

color of the Newark sandstones is sustained by future investigations, 

it will follow that the debris composing these rooks was deposited in 

lakes or estuaries where it was not subjected to prolonged washing by 

waves or exposed to the action of natural reagents which have the 

power to dissolve it. Had the debris been deposited in the ocean and 

exposed to the action' of waves and currents, the sands would have been 

more thoroughly assorted than we now find them.. We should expect, 

also, that the attrition produced by the wash of the waves under such 

circumstances would have scoured off the incrustation of ferric oxide. 

A microscopical examination of a number of samples of the sand ob-. 

taiued by washing residual deposits failed to show that the iron-stained 

grains thus separated were more angular than the sand grains in an 

average sample of Newark sandstone. This indicates that the latter 

was deposited rapidly and not worn and rounded by prolonged wave 

action.

The chemical reaction of sea water on incrustations of this character 

has not been investigated.

The character of the deposits that result when d6bris is contributed 

to swamps or lakes rich in organic acids is illustrated, by the middle or 

carbonaceous member of the Newark system exposed in the coal fields 

of Virginia aud North Carolina. These beds are sometimes highly 

charged with iron, but it is combined v?ith sulphuric and carbonic 

acids. The rocks are therefore not red and the grains of sand composing the strata in pare are not incrusted in the manner observed in 

the red sandstone.

The assorting of residual deposits formed by the subaerial decay of 

crystalline rocks, like those composing the Appalachian crystalline belt, 

would afford material for the formation of stratified beds of diverse litho. 

logical character. When the rocks were much decomposed beds of iron. 

jBtaiued sand would predominate, iiiterstratified with layers of red clay

(577)
46 SUBAEKLAL DECAY OF ROCKS. [uuu,52.

formed by the accumulation of finer and more thoroughly decomposed 

material unshed from the laud. When the parent rock was disintegrated without suffering marked decomposition, light-colored and less 

homogeneous beds would be formed. The more thorough the subaerial 

decay, therefore, the more homogeneous and the more ferruginous would 

be the resulting sedimentary beds.

When the residual deposits of an ancient laud surface contribute to 

the filling of lakes or estuaries the shore deposits should be coarse 

and contain fine red sediment in the interstices between the pebbles. 

Near the land such a formation would probably be a light-colored conglomerate or breccia, cemented with fine ferruginous clay ; farther seaward the sediment should not only be finer but also more homogeneous 

and more completely iron-stained.

It has been remarked by several geologists that the sandstone forming the lower portion of the Newark system of the Southern States is 

more highly colored than the similar rocks in the upper portion of the 

same formation. This may be due to a removal of the more thoroughly 

decomposed residual deposits from the surrounding shores before the 

upper portion of the series was laid down.

P. vou liichthotenV view of the possible origin of red deposit agrees 

essentially with the hypothesis here proposed, as is indicated in the following citation, which follows a statement that great quantities of the 

residual soils of Brazil are now being carried to the sea and deposited 

as red sediments on the floor of the ocean. lie says:

Afar more .prominent part would bo played by the laterite if a wave of abrasion 

swept over Brazil scouring away the red soil formed in the course of centuries, in 

order to allow its redeposition in the ov'erplaccd sediments (transgrcdirendcn Scdimcntcn). This has been the origin of many formations of by-gone time, and it is 

proper to note that the mightest accumulations of redmassesof sediments occur in the 

strata of the Rothliegende, which often appear in the manner of transgressions, and 

that 1 hese strata were preceded in time by the Carbon! ferous epoch, in which, to jndgo 

from analogy with ttie present time, there must have occurred the most intense deep 

decay of rock, involving the formation of latetite.

In Part I of this paper it.has been shown that the residual deposits 

of warm, humid regions are red, and that the corresponding deposits of 

arid regions are light colored, usually gray or yellow-brown.

It seems to follow from this that the red rocks of the Newark system 

and of the liocky Mountain Red Beds were formed from the debris of 

lands that had been long exposed to the action of a warm, moist atmosphere. This same suggestion has been made by liichthofeu, as is 

shown by the citation just given.

The conclusions presented in the past few pages will perhaps appear 

more definite if we consider briefly the various hypotheses that have 

previously been advanced to account for the red color of certain formations.

: . ^

1 Fiihrer fiir Forschungsreisendo, Berlin, 1880, pp. 460,467,

(578)
HU88BLL.J COLOR OF LACUSTRAL DEPOSITS. 47 

PREVIOUS HYPOTHESES.

A. C. Eamsay, 1 after studying the Old Bed Sandstone and other formations in Europe which arc largely composed of iron-stained rocks, advanced the hypothesis that lake deposits are usually red, and that their 

color is due to the presence of peroxide of iron, " the iron probably 

having found its way into the water as a carbonate, which, by contact 

with the air, afterwards became peroxidized, and incrusted the sedimentary grains as a thin pellicle.'7- A study of lacustral deposits at many points in the United States 

has shown that the generalization quoted above can not be accepted 

without important qualifications. The Quaternary and Tertiary lacustral beds of this country are light colored, almost without exception.2 

The grains of sand composing them in large part are not incrusted with 

ferric oxide. The sediments now forming in the saline and alkaline 

lakes of the arid region of the Far West are not iron-stained and do not 

differ in this respect from the sediments now being deposited in the 

Laurentian lakes.

In describing the Tertiary and post-Tertiary lake deposits of the 

western part of the United States, F. V. Hayden :i says :

The prevailing color is light brown-gray or nearly white, perhaps iu some instances 

a cream color. There is a remarkable similarity in the color as well as the composition of these deposits all over the West, in Montana, Oregon, New Mexico and Texas.

F. von Kichthofen 4 describes the lake loess of China, which appears 

to be similar in every way with the playa deposits of the arid region of 

the United States, as being whitish yellow in color.

The observations indicate that the reverse of Earn say's hypothesis is 

true, namely, that lacustral deposits in general are not characterized 

by a red color.

All the examples given above of lacustral deposits now forming, 

however, are located in regions that do not give evidence of having 

suffered marked subaerial decay. The existing lakes of this country 

do not receive the d6bris of lands that are deeply covered with residual 

deposits. In the South Atlantic States, where the greater portion of 

the country is buried beneath decomposed rocks rich in iron, the stream 

deposits are largely iron-stained sands, containing grains of feldspar 

and mica. Were there any lake basins in this region it is evident they

1 On the physical relations of the New Red Marl, Rluefcic Beds, and Lower Lias. 

Quart. Jour. Geol. Soc. London, Arol. 27, pp. 1S9-20G. Also, On the Eed Rocks of 

England of older date than the Trias. Ibid., 241-256.

s The only exception known to me is the red clay deposited during the Pleistocene expansion of Lakes Superior and Michigan. Geological Survey of Wisconsin, 

1873-'7'J, vol. 1, p. 292.

3 Notes descriptive of some geological sections of the country about the headwaters 

of the Missouri and Yollowstone Rivers. Bull. U. S. Geol. Geog. Survey Terr., 

Washington, 187(i, vol. 2, p. 201.

4 China, vol. 1, p. 81.

(579)
48 SUBAERIAL DECAY OF ROCKS.

 

would becoaie tilled with material of the same character as that now

forming the stream beds and flood plains. Lacnstral deposits accumulated under such conditions would comprise iron-stained sands interstratified with layers of red clay, etc., which, in general, would be practically identical with the rocks of the Newark system.

The hypothesis proposed by Ramsay necessitates that ferrous carbonate should be contributed in solution to lakes of great size in sufficient 

quantity to saturate their waters, and that its oxidation or change to 

ferric oxide should go on more or less continuously throughout the time 

the sediments were accumulating. This process, if I understand it 

aright, would be practically the same as that by which bog ores are 

formed. This complicated series of chemical reactions might furnish 

an explanation of the color of local deposits, but it does not seem, applicable to s,uch great formations as the Old Bed Sandstone of Europe or 

the Mesozoic red sandstones of this country.

J. AV. Dawson, 1 in an article "On the coloring matter of red sandstones, and of grayish ami white beds associated with them," states that 

the coloring matter of the Carboniferous sandstones, red conglomerates, 

etc., of Nova Scotia " is the peroxide of iron in a very fine state of division, having indeed rather the aspect of a chemical precipitate than of a 

substance triturated mechanically. . In the clays and shales it is usually 

very uniformly diffused through the mass; in the sandstones and conglomerates it is principally contained in the argillaceous matter which 

occupies the interstices of sand and pebbles, and it also stains the surfaces of these fragments." Dawson supposes that the ferric oxide was 

derived from the oxidatiou, through the action of igneous agencies, of 

iron pyrites disseminated through the rocks from which the Carboniferous sandstones were derived. This view has been discussed at some 

length by A. A. Julien in his essay On the Geological Action of the 

Humus Acids, 2 who shows that the coloring matter in the rocks described by Dawson must have been derived from the decomposition of 

the hornblende, chlorite, orthoclase, and the iron garnets as well as 

the pyrites of the parent rock.

The conditions under which the Carboniferous sandstones of Nova 

Scotia received their red color were repeated in the same, region when 

the Newark sandstones were deposited. In describing the latter rocks 

A. W. McKay observes : 3

The color of these beds seems to be derived from tlie iron contained in the neighboring metamorphic rocks. It occurs in these hitter in three different forms : (1) There is

'Quart. Jour. Geol. Soc. London, vol. 5, 1848, pp. $25-30. See also Acadian Geology, 

by J. W. Dawson, 3d ed., 1878, pp. 622-823, and On the parallelism of the rock formations of Nova Scotia with those of other parts of America, by the same author, 

Proc. Am. Assoc. Adv. Sci., 10th (Albany) meeting, part 2, p. 20.

2 Proc. Am. Assoc. Sci., 28th (Saratoga) meeting, 1879, pp. 405,408.

3 The Red Sandstones of Nova Scotia. Kept. British Assoc. Adv, gjci., 35th (Birmingham) meeting 1865, part 2, p. 67,

(580)
BUBSEH-.] ORIGIN OF THE COLOR OF NEWARK SANDSTONES. 49

a quantity of it distributed generally throughout tho slates and shales, of which 

these strata arc composed ; (vJ) there are veins and beds of specular iron ore, as In 

the Devonian rocks of Nictaux ; and (3) it occurs in the shape of bisulphide of iron or 

iron pyrites. When these iiictarnorphic rocks were wprn away the iron set free was 

oxidized by contact with the atmo.spb.ere and mixed up with sediment as it was laid 

down.

J. D. Dana 1 attributes the red color of the Newark sandstone's to 

the oxidation of the iron which they contain, through the agency of the 

intruded sheets and dikes'of trap. 2 As the red color, is not confined 

to the vicinity of the igneous intrusions, and is disseminated with remarkable uniformity through great thicknesses of sandstone, 3 we <tre at 

a loss to see how the iitcrusting of the grains of sand with ferric oxide 

could have been brought about by the heat of the intruded rocks. This 

explanation fails entirely when applied to similar iron-stained sandstones which have not been disturbed by igneous injections. It also 

fails, in part at least, when applied to regions in which the trap is not 

intrusive, but was poured out as an overflow, and subsequently became 

buried beneath sedimentary deposits.

In another place Dana'1 refers the red color of the sandstones of the 

Connecticut Valley to an alteration of the iron they contain by the action of heat resulting from orographic movements.

As stated by him, the change produced by the tilting of the rocks of 

the region referred to into their present inclined position "stopped short 

of metainorphism, the sandstones being only reddened and partially 

solidified." Applying this hypothesis to the Virginia aud North Carolina coal fields, where the strata are as highly inclined as in the Connecticut Valley, one would expect that the rocks would have the characteristic color found in other portions of the same formation, providing 

that a change in color resulted from the tilting of sedimentary beds. 

The facts are, however, that the carbonaceous rocks iu the coal fields 

referred to show no alteration in color, and the coal they contain is 

still highly bituminous, except in the immediate neighborhood of trap 

dikes. That reddening is a general result of rnetamorphism, as is assumed in the quotation given above, can scarcely be accepted iu the 

presence of so many examples of metamorphosed rocks that are not red. 

The view that the red color of the Newark sandstones is due to the 

heat of the intruded trap was advanced in substance many years since 

by E. Hitchcock 5 and J. G-. Percival." That the trap could have been

1 Manual of Geology, 1875, p. 420.

2 Tuis hypothesis has also been controverted by Julieu, loc. cit.

3 Among the many illustrations of the thickness of the iron-stained rocks of the 

Newark system that might be given are the records of a well over 1,400 feet deep ac 

Durham, N. C., in which the rocks, with some exceptions, are reddish brown aud remarkably similar in composition from top to bottom. Other wells of still greater 

depth in New Jersey and the Connecticut Valley have given similar results.

4 Am. Jour. Sci., 3d series, vol. 5, 1873, p. 431.

 ' Kept, on the Geol., Min., Bot., and Zool. of Massachusetts, Araherst, 1833, p. 242. 

(; Gool. Connecticut, Now Haven, 1842, p. 430. 

Bull. 52 4 (581)
50 PUBAERIAL DECAY OF ROCKS. [MULL. 52.

instrumental in producing the wonderful results assigned to it by the 

authors quoted above has been successfully refuted by W. M. Davis, 1 

who has shown by observations made by himself and others, that as a 

general rule the baked strata near the trap are not so red as the unaltered layers farther, away. Davis has also pointed out the fact that 

red sandstones occur in regions so far removed from igneous action 

that they could not be influenced by it.

B. K. Emerson2 attributes the red color of a portion of the sandstone 

of tht^ Connecticut Valley to iron derived from volcanic dust thrown 

out of'certain small volcanoes, the remnants of which he has recently 

discovered in Hampshire County, Mass.

G.H.Gook3 has suggested in reference to the coloring matter contained 

in the Newark sandstones and shales of New Jersey, that the iron in 

the coloring matter with which the grains are iucrusted was dissolved 

from the trap rocks of the region by percolating waters and redeposited 

in the sandstone. At least this is my interpretation of the following 

passage:

The deep red color of this formation shows its large percentage of oxide of iron, 

which in some of the shales amounts to 10 per cent., though it is usually much smallor. 

It is in the form of oxide, and forms the paste or cement of the mass. Where did this 

iron ore come from ? Very little is found in the gneiss from which the sandstone has 

been formed, and there is not much in the lower and light-colored beds of the sandstone. The trap contains magnetic iron ore in little particles; so much that almost 

any specimen of it powdered will yield some to the magnet, and the rock itself is 

quite magnetic ; irregularly so, however, as it produces local attraction and disturbance of the surveyor's compass. .Did the iron ore comefroni the same source which suppUed the trap ? It might have come thus, and, dissolved in water, it could have made 

the coloring material and furnished the precipitated oxide of iron. It is very evident 

that the high-colored sands in the Cretaceous and Tertiary formations were white 

when deposited and have been discolored by water containing oxido of iron ; for we 

often iind little nests of perfectly white sand surrounded on all sides by red sand full 

of oxide of iron; and in some cases a perfect shell of sand, cemented by oxide of iron

into stone, is filled with a mass of loose sand. The same kind of agency has, undoubtedly, supplied the coloring substance of the Triassic rocks, though it appears 

to have been done at the time of its deposition.

The fact that the sandstones are not more highly colored in the neighborhood of the trap ridges than at a distance of several miles from 

them, as has already been shown, is in direct opposition to the hypothesis presented in the above quotation.

It is well known also that with the exception of samples taken from 

near the outcrops of the trap ridges in New Jersey, the microscope fails 

to show that these rocks have suffered to a marked extent by the solution of their constituents, as is also proven by the discovery of metallic

l Ou the relation of the Triassic traps and sandstones of the eastern United States ; 

in Bulletin of the Museum of Comp. Zoology at Harvard College, vol. 7 (Geological 

series, vol. 1), No. 9,1883, p. 300.

3 Gazetteer of Hampshire County, Mass., 1654-1887. By W. B. Gray, Syracuse, N. Y. 

(1888), p. 18.

3 Geol. New Jersey, 1868, p. 333. I

(582) ;
RUSSELL.] OKIGIN OF THE COLOR OF NEWARK SANDSTONES. 51

iron iu them. 1 Even if the whole of the iron contained in the trap rocks 

of New Jersey had been removed and redeposited uniformly throughout 

the accompanying clastic beds, it could scarcely have 1'urnished sufficient ferric oxide to give them their characteristic-colors. This statement is sustained, we believe, by the following considerations. An 

average of seventeen analyses of trap rock from New Jersey gives 12.o 

per cent, of ferric oxide.2 The percent, of ferric oxide (Fe2Oy ) contained 

in five samples of Newark sandstone from New Jersey *is as follows 3 :

(1) Brown sandstone from Whitehall ..................... 3.83

(2) Bro vvn sandstone from Worteudykc.................... 3.00

(3) Brown sandstone from Littlo Falls .................... 1.34

(4) Shaly brown sandstone, Belleville quarries ............ 5.74

(5) Light drab sandstone from near Plaiuh'eld, N. J........ 3.03

Average ........................... ....:.......... 3.39

These analyses show that the trap rock contains about 3.7 times as

much ferric oxide as is contained iu average samples of the brown 

sandstone of the associated sedimentary beds.4 It is impossible to coinpare the mass of the trap in New Jersey with the mass of the associated 

sedimentary beds, but we may assume with a fair degree of probability that the masses of the rocks mentioned are to each other as the 

areas of their outcrops. From the geological map accompanying the 

Annual Eeport on the Geology of New Jersey for 18811 find that the 

outcrops of trap occupy 225 square miles, and the outcrops of the sedimentary beds 1,24.5 square miles/' That is, the ratio of the area occupied 

by igneous rocks is to the area occupied by sedimentary rocks of the 

same system as 1: 5.5. This rough computation seems sufficient to 

show that the Triassic igneous rocks do-not contain as much ferric 

oxide in the aggregate as is contained in the sedimentary beds, which 

are supposed to have derived their color from them.

The facts presented above in. reference to the uniformity of color of 

the Newark saudstones, the unaltered condition of the trap rocks, and 

the excess of iron iu the sedimentary beds over that contained in the 

associated igneous rocks are true not only for New Jersey, but throughout all the Newark areas from Nova Scotia to South Carolina, and, I

'Ann. Kept. Geol. Survey New Jersey, 1884.

" Geology of New Jersey, 1868, pp. 215-218..

:! The analyses numbered 1 to 4 are by Charles Catlett, of the U. S. Geological 

Survey, and re present the per cent, offerric oxide (Fe^On) obtained by digesting samples of sandstone in acid, and therefore give the per cent, of ferric 'oxide iu the 

cementing material of the samples. No. 5 is from the Geological Survey of New Jersey, 1868, p. 509. Other analyses are given on .pages 515, 51C of the same report.

 'Pcrsifor Frazer has computed that there are contained in every mile,of strike one 

chain in dip and one yard in thickness of the Newark sandstone, 6,193.44 long tons of 

ferric oxide. Traus. Am. Inst. Min. Eng., vol. 5,1876-77, p. 501.

5 The area given above for the outcrops of the trap rock is greater than would be 

obtained if the surface of the conn try wore reduced to ;i plain, for the reason that the 

edges of the trap sheets stand in relief and form nionoclinal hills.

(583).
52 SUBAERIAL DECAY OF ROCKS. [BULL. 52.

believe, militate strongly against the hypothesis that the clastic beds of 

the Newark system derived their ferric oxide from the sheets and dikes 

of igneous rock which traverse them.

On pressing to the extreme the hypothesis proposed by Cook, it might 

be assumed that the sandstones and shales still existing in the Newark 

basins received their coloring matter from those portions of the intrusive rocks which have been eroded away; the iron having been leached 

out as decomposition progressed, and redeposited in the sandstones at 

a lower level. This extension of the hypothesis meets the objection 

that the proportion of trap to sedimentary beds in that portion of the 

formation which has been removed by erosion was probably about the 

same as in the terranes remaining, and that the iron derived from 

the trap would have been insufficient to color the clastic beds with 

which it was intimately associated. Again, it might be assumed 

that the sheets and dikes of trap now remaining led up to vast overflows of igneous rock which have been entirely removed, and that the 

disintegration of this supposed lava sheet supplied the ferric oxide 

of the clastic beds beneath. These extensions of the hypothesis, however, are so fanciful, that they need not be considered at the present 

time.

In the last line of the quotation given on page 50 the statement is 

made that the coloring substance of the Newark rocks appears to have 

been supplied at the time of their deposition. This manifestly could 

not have been the case had the coloring matter been derived from the 

leaching of the trap rocks, as suggested in previous parts of the same 

quotation, for the. reason that the trap is largely intrusive, and was 

forced in among the sedimentary beds after their deposition and consolidation.

In discussing the origin of the characteristic color of the rocks of the 

Newark system in New Jersey, J. S. Newberry l states that 

The New Jersey highlands, as well as other portions of the Bine Ridge belt, are 

known to contain great quantities of iron ore, and the erosion of the gneiss which 

forms this belt must necessarily result in the distribution of a large amount of iron. 

Hence it is not surprising that the shales and sandstones all contain enough of this 

element to give them a red or reddish color whenever it is in the form of the anhydrous peroxide. The fact that it is generally in this condition, and therefore the 

rock is red, proves that it contained little or no organic matter when deposited, for 

whenever decaying organic matter is present in any considerable quantity it reduces 

the peroxide of iron to protoxide, and makes the color, so far as influenced by the 

salts of iron, gray, green, or blue. Where the organic matter is in very large quantity, it imparts the characteristic color of carbon, and makes the shale of limestone 

which contains it black.

The hypothesis that rocks are red because they do not contain organic matter has been stated with some minuteness by H. Newton,2

'Moii. U. S. Geol. Survey No. 14, 1888, pp. 7, 8.

2 Kept, on the Geol. and Resources of the Black Hills of Dakota, Washington, 1883, 

pp. 138,139.

(584)
KUB8ELL.1 ORIGIN OF THE COLOR OF THE RED BEDS. 53

in explanation of the origin of the color of the Red Beds of the Kocky 

Mountain region. I quote his discussion in full:

The large percentage of peroxide of iron in the Red Beds, to which they owe their 

bright red color, bears an interesting relation to the absence of fossils. The material 

of which sediments arc formed is derived by the various processes of denudation from 

rocks of older laud surfaces. Whatever iron they contain is dissolved from the land 

and transported in the condition of protoxide or some protosalt, such as the carbonate, and the process is facilitated by the presence of carbonic acid in the water. Now 

iron occurs in these older rocks as peroxide and protoxide, the former of which is 

soluble and the latter insoluble in water. The peroxide, however, by the action of 

organic matter, such as is held in solution by boggy waters, may be deprived of a 

portion of its oxygen and converted into protoxide, and thus rendered soluble. If 

the iron-bearing water is confined, as in a shallow basin, and exposed long to the 

action of the atmosphere, the protoxide of iron absorbs oxygeu, and is precipitated as 

the insoluble red peroxide of iron. If, however, plaut or animal life be present in 

sufficient quantity, this oxidation is prevented. In case but little foreign material 

clay or sand has been brought by the waters, the deposit will be an iron ore: in the 

absence of organic matter, the peroxide or brown hematite; or in its presence, the 

protocarbonate, such as the iron-ore beds of the Coal Measures. Bat in case large 

quantities of foreign material are deposited from the waters at the same time, there 

will bo produced, in the absence of life, a brown or red clay or sandstone, and in it,s 

presence a white or light-colored formation containing the iron as a protoxide. This 

question of the removal and deposition of iron has been ably elucidated by Dr. Newberry and others, and Dr. Hunt " can hardly conceive of an accumulation of iron, 

copper, lead, silver, or gold in the production of which animal or vegetable life has 

not either directly or indirectly been necessary." The point to bo established by this 

seeming digression is this, that, reasoning from the condition in which the iron is 

found in the Red Beds, we must conclude that there could have been little or no life, 

animal or vegetable, in the waters from which they were deposited. The conclusion is strengthened by the fact of the presence of largo quantities of gypsum, which 

has been derived from the evaporation of saline waters. The degree of saline concentration which the precipitation of gypsurn indicates would be highly inimical to 

life.

That the chemical processes mentioned in this hypothesis are active 

in the segregation of .ores there seems abundant evidence, but that the 

color of great terranes can thus be accounted for is not so definite.

This hypothesis implies that red rocks are the deposits of inclosed 

basins, which it is known is by no means the universal rule. It also 

suggests that red deposits should now be accumulating in the inclosed 

lakes of arid regions. This we know is not the case. Not a single instance of the deposition of iron-stained beds in the inclosed lakes of 

this country has been observed, although a number of cases are known 

\vherc gypsum and other salts are being deposited. The lakes in which 

these precipitates are being thrown down are in a'desert region and are 

free from notable quantities of organic matter.

There are striking exceptions, too, to the. frequent statement that 

red rocks are destitute of fossils. Certain sandstones near Taylorsville, Pluinas County, Gal., which are even brighter red than the normal 

sandstones of the Eed Beds or of the Newark system, are rich in a 

great variety of marine invertebrates.

(585)
54 SUBAERIAL DECAY OF ROCKS. [HULL. 52.

A. H. Green,1 in a lecture on the geology of coal, remarks that the 

Middle and Lower Coal Measures and the Millstone Grit of England 

are blue and gray when protected from the action of the air, but of various shades of brown and yellow at or near the surface. On the other 

hand, the prevailing colors of the Tipper Coal Measure are red, purple, 

and mottled red and green. The color of the red rocks " is caused by 

every grain being coated by a thin skin of ferric oxide." This coating 

of coloring matter is supposed to have been deposited on the grains of 

sand from the waters of the inclosed lakes in which it accumulated, 

which were "red as blood, owing to the presence in large quantity of 

finely divided ferric oxide." The source of the ferric oxide is thought 

by Green to have been of volcanic origin, and to have been derived from 

the decomposition of ferric chloride arising from neighboring volcanoes. In reference to this hypothesis A. A. Julien observes: 2

Especially is there no need of ascribing to a volcanic sublimate the source of the 

ferric oxide. The western prolongation'of the Archeau rocks of the Scandinavian 

peninsula, referred to by this author, probably covered by heavy vegetation and 

swamps, must have afforded an ample area and volume of ferruginous materials for 

the solvent action of liurnus acids on a vast scale and through, a long period, sufficient to liave supplied the ochreous cement of the sandstones in the Carboniferous 

seas.

The hypothesis suggested by Green and supplemented by Julien falls 

in the same category as the hypotheses proposed by Kamsay, Newton, 

and Newberry, and is open to the same objections.

The red color frequently seen on the surface of many outcrops, which 

are light-colored when uuweathered, is supposed by T. B. Comstock 3 

to have resulted from the action of ozone in the atmosphere on the iron 

contained in the rocks in small quantities.

The red coloring matter of the Newark and other similar rocks has 

undoubtedly been assumed by many to have resulted from the infiltration of ocherous matter after the fragmental grains of which they are 

composed were deposited. Microscopic examination of thin sections of 

the rocks in question, however, does not sustain this suggestion. As 

shown by the microscope, the sand grains are seldom in direct contact, 

but are separated by the incrustations surrounding them, which would 

not be the case had the red matter been brought in by infiltration. The 

spaces between the sand grains are usually completely filled with ocherous matter, and it is possible that a part of this at least is due to infiltration or to a re-arrangement of the finer material of the deposit; the 

same result would be expected, however, from the deposition of the

1 Coal, its history and uses, by Professors Green, Miall, Thorpc, Riicker, and Marshall, London, 1878 pp. 62-66.

2 On the geological action of the humus acid, Proc. Am. Assoc. Adv. Sci., 28th 

(Saratoga Springs) meeting, 1879, pp.'404.405.

3 Geological report. lu report upon the reconnaissance of northwestern Wyoming, 

by W. A. Jones, Washington, 1874,' 8vo., p. 178.

(586)
KUSHELI..J COLOR OP DEEP SEA SEDIMENTS. 55

finely divided ocherous material at the time the sand grains were accumulated.

The great thickness of the strata through which the coloring matter 

is sometimes uniformly disseminated can not be accounted for on the 

hypothesis of secondary infiltration. Besides, the iron-stained rocks 

are frequently interbedded with gray and often with white sandstones, 

showing that the coloring matter was deposited at the same time as the 

sand grains with which it is so intimately associated and not subsequently introduced. The interstratificatiou of colored and nncolored 

layers is also opposed to the hypothesis that widely spread change in 

the color of rocks has been produced by igneous intrusion.

EXCEPTIONS.

The considerations presented in the present paper in explanation of 

the color of the iron-stained rocks manifestly do not apply to sandstones 

and allied rocks formed principally of feldspar and quartz in which the 

color is inherent in the composing minerals.

Again, it is well known from the explorations of the Challenger expedition and of the various surveys made by the U. S. Fish Commission, 

that red clay is found in the abyssal portions of the ocean. This clay, 

as shown by C. Wyville Thomson and others, is a subaqueous residual 

deposit, formed in part of the insoluble portions of the shells of mollusks 

and of microscopic organisms, which descend principally from the surface of the ocean and are partially dissolved during their subsidence. 

It is also composed in part of pumiceous particles, which have been 

drifted to great distances on the surface of the sea, together with volcanic, aerial, and cosmic dust. The material from all these sources has 

been long exposed to the solvent action of sea water, so that only the 

comparatively insoluble residue finally accumulates on the bottom in 

the deeper parts of the ocean. Owing to the extreme slowness with 

which ordinary sedimentation takes place in those portions of the ocean 

most remote from land, the residual deposits mentioned above are allowed to accumulate until they form homogeneous layers of broad extent and perhaps of great thickness. Although the red clay resulting 

from the solution of limestones, etc., under subaerial conditions, and the 

red cla.y resulting from the subaqueous decay of pelagic shells, dust, 

etc,, are similar, yet, owing to their different associations, one is not 

ikely to be confounded with the other. As the history of the formation 

of the oceanic clay is foreign to the purpose of the present paper, further notice of it is omitted.

Other exceptions might be cited, as when the colors of .rocks are altered by volcanic heat or by the burning of carbonaceous strata. Fresh 

lavas and lapilli deposits are frequently brown and red, and would 

make sedimentary beds of the same colors if deposited in water. Such 

cases usually explain themselves, however, and need not be discussed 

at the present time.

(587)
56 SUBAERIAL DECAY OF EOCKS.

III. RESUMfi.

The formation of red deposits from the debris of rocks that are not 

red, but contain iron in the hornblende, mica, chlorite, magnetite, garnets, pyrites, and other minerals of which they are composed, evidently 

necessitates that the minerals holding the iron should be decomposed 

and the iron oxidized. This process we now find in operation over large 

portions of the earth's surface in the formation of residual deposits, of 

which the terra rossa of Europe, the laterite of India, the red earth of 

Bermuda and the residual clays of the southern Appalachian region are 

the best known examples. The residual deposits resulting from the 

subaerial decay of crystalline rocks agree both in chemical composition 

and in the manner in which the grains of sand are incrusted with ferric 

oxide, with the sandstones of the Newark system, and with other formations of a similar lithological character. Moreover, the residual deposits of the Southern States are assorted and deposited by streams without losing the ferric oxide which incrusts the grains, thus showing that 

they are capable of forming iron-stained sandstones and shales.

Thehypothesis advanced in view of these facts is, that the sands forming the sandstones of the Newark system and other similar formations 

received their incrustations of ferric oxide during the subaerial decay 

of the rock from which they were derived.

(588)
BIBLIOGRAPHY.

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(589) 57
58 SUBAERIAL DECA.Y OF ROCKS. [BULL.52.

Dana, J. D. United States Exploring Expedition; 18158-1842 (geology). Decomposition .of rocks in Australia, pp. 513-5Hi; in Tahiti,p.298; inTierra delFuego, p. 

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 Manual of geology, 1875, pp. 487-496. *

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1590)
RUSSELL.] BIBLIOGRAPHY. ' 59

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 Note sur Falt6ration des rocbes quaternaires dcs environs de Paris, par les agents 

atmospb6riques ; Bull. Soc. ge~ologiqtie France, 3d series, vol. 5, 1877, p. 298.

 Scconde note sur le qiiatemairo des environs de Paris. Rdponse aux observations de M. H6bert; Bull. Soc. ge~ologiquo France, 3d series, vol. 5, 1887, pp326-328.

 Quatemaire ct diluvium rouge; ibid., A'ol. 7,1879. pp. 209-217.

 Me"nioire sur les phtSiioineues, d'alte"ratiou des d6pots snperficiels par 1'inh'ltratiou dcs eanx rne'te'oriqiies; M6ui. Acad. Sci. Belgique, vol. 44, 1882. 

Wadsworth, M. E. Some instances of atmospheric action on sandstone. Proc.

Boston Soc. Nat. Hist., vol. 22, 1882-'83, pp. 201-203.

Wall, G. P., and J. G. Sawkins. Rept. Geol. Trinidad; London, I860, pp. 69-82. 

Webster, J. W. Remarks on the geology of Boston and its vicinity ; Boston Jour.

Phil. Arts, 1825. Disintegration of greenstone 'described on pages 284, 285. 

Wliitaker, W. On subaerial denudation, etc. ; Geol. Mug., London, vol. 4, 18H7,

pp. 447-454,483-493. .

 -Mein. Geol. Survey Great Britain. Tbe Geology of Middlesex, Hertfordshire, 

Buckinghamshire, Berkshire, and Surrey, London, 1864; pp. 63-66.

 On snbaerial denudation ; Geol. Mag., London, vol. 4,1867, pp. 327-328, 447-454,

483-493.

White, C. A. Rept. Geol. Survey Iowa, vol. 1,1870, p. 124. 

Whitney, J. D. Rept. Geol. Survey Wisconsin, vol l,p. 121, 1862.

 Climatic changes in later geological time; Mem. Mns. Conip. Zoo'1. Harvard

College, vol. 7, part 2. 

Wiiichell, N. H. Second Ami. Rept.. Geol. and Nat. Hist. Survey Minnesota, 1873,

pp. 166, 207. 

Woodward, H. B. Geol. England and Wales, 2d ed., London, 1887, p. 596.

(593)

INDEX.

A.

Page. 

Alabama, decay of rocks in ..............:... 19-23

Analysis of residual clay from Gary, N. C.. 13 

of decomposed trap from North Carolina .................................. .18

of unaltered trap rock from the Newark system........................... 18

of Clinton ore from Alabama........... 22,23

of Trenton limestone................... 24

of residual claya......................24,25,40

 of Knox dolomite ....................... 25

of red earth and coral from Bermuda... 29 

of water from the James River, Virginia ................................. 38

of river waters in America and Europe. 38,39 

of Newark sandstone .................. 51

Anson County, N. C., trap dikes in ........ 16

Appalachian Mountains, decay of the rocks

of the ........................ 15,18-20,32,34

scenery of.............................. 19

Arizona, color of river'and lake beds in.... 42

Artesian well at Durham, N. C............. 49

Asheville, N. C., scenery near ............. 19

Asia, distribution of laterite in southern... 28 

Atalla, Ala., depth of decay in Clinton ore

near.............l.................... 22,23

Atlanta, Ga., geological work near......... 10

decay of rocks near..................... 19

B. 

Bahamas, red earth of................. 25,28,29,33

Baryta in residual clays.................... 43

Belt, T., on rock decay in Central America. 28 

Bermuda, red earth of.................25,28,29,33

Bibliography............................... 57-61

Birmingham, Ala., decay of Clinton limestone near............................ 22,23

Bischof, S., cited on composition of river

waters ............................... 38

Blanford, W. T. (See Medlicott, H. B.) 

Bowlders of disintegration in trap dikes.... 17

Brazil, redeposition of red soil of........... 46

Bricks, use of terra rossa in the manufacture of................................ 43

Bnrbank, L. S., cited on rock decay........ 13

C.

California, decay of rock in................ 26,27

color of sandstone in.................... 53

Carboniferous rocks of Alabama, decay of.. 23

Page. 

Carolitias, rock decay in the........i....... 12,13

Gary, N. C., rock decay near............... 13

Catlett, C., analyses of Newark sandstone

by.................................... 51

Cave earth, origin of....................... '25

Central America, rock decay in............ 28

Chamberlin, T. C., and E. D. Salisbury, cited

on the decay of rocks in the driftless

area of the Mississippi Valley .... .25,26,41 

Charlottesville, Va, geological work near.. 10 

Chatard, T. M., analysis of decomposed trap

from North Carolina..................17,18

Chert,decay of............................. 21

left by the decay of dolomite........... 21

Chester, S. C., geological work near........ 9

Chestnut Hill, Pa., analysis of kaolin from. 39,40 

China, color of the lake loess of............ 47

Climate, relation of, to rock decay.......... 30-34

Clinton limestone near Atalla, Ala ........ 23

Clinton ore from Alabama ................. 22,23

Colfax,Cal., rock decay near............... 27

Colorado, absence of rock decay in......... 26,27

Cook, Gr. H., on the red color of certain

rocks ................................ 50

Coosa Valley, Alabama, post-Carboniferous

erosion in............................ 20

residual deposits in .................... 21

Crosby, "W. O., explanation of the color of

red soils by .......................... 41,42

Croton River, inorganic matter in water of. 39 

Crozet Island, climate and absence of soil

on ................................... 30,31

Curagao,rock decay on .................... 28

D.

Dalmatia, deposits of terra rossa in......... 28

Dana, J. D., observations in Australia, TaKiti, etc., by..........................

cited on the red color of certain rock... 

Dawson, J. W., cited on the origin of the

red color of certain rocks ............

Dewees, T. H., cited on the decay of Clinton

limestone in Pennsylvania...........

Dikes of trap in the Newark system, decay

of.................................... 16-18

Dolerite...............................36,17,18,39

in the Great Appalachian Valley, decay

of..................................21,24,23

Durham, N. C., depth of an artesian well

at.................................... 49

48

22

(595) 63
64 INDEX.

E.

Page. 

Economic products of residual clays....... 43

Emerson, B. K., cited on the red color of

certain rocks......................... 50

England, residual earths in ................ 21

Erosion in the Great Appalachian and the

Coosa Valleys, measure of............ 20

Europe, the terrarossa of.................. 25

F.

Far "West, absence of rock decay in the .... 25-27

Field work................................. 9,10

Fontaine, "W. M., on rock decay in the Appalachian region........................ 15

Fossil ore. (See Clinton ore.) 

"(Frazer, P., cited on iron in Newark sandstone................................. 51

Fuchs, Th., on relation of climate to rock

decay in Europe ..................... 28,32

G.

Gabb, W. M., cited on rock decay on Curacao..... .............................. 28

Gadsden, Ala., depth of decay in Clinton

ore near.................... ....... 22

Galena in residual clays.................... 43

Genth, F. H., analysis of kaolin by......... 40

Glaciers in the southwestern part of the

United States........................ 26

Gold in residual clay........ ........... 15,43

Great Appalachian Valley, geological work

in.................................... 9,10

defined................................. 20

amount of erosion in ................... 20

decay of rocks in....................... 20-26

red earth of............................ 25

Greece, deposits of terra rossa in........... 28

Green, A. H., cited on the red color of certainrocks ............................ 54

Greenyille, S. C., geological work near...... 1 o

rock decay near ...................... 14

Guyot, Arnold, use of the term "Great Appalachian Valley " by................ 9

H.

Hampshire County, Mass., volcanic dust in.

Hartt, C. F., reference to observations in 

Brazil................................

Hawes, G. "W., analysis of trap rock by..... 

thin sections of sandstone examined by

Hayden, F. V., on the color of lake deposits 

in the Far West......................

Hillebrand, "W. F., analysis of dolomite and 

of residual clay by...................

Hitchcock, E., cited on the red color of certain rocks............................

Hudson River, solids in the water of.......

.Hunt, T. S., on rock decay in the Appalachian region .........................

OH the relation of climate to rock decay ..................................

50

28

17,18

44

47

25

49

39

15

33

Page. 

Idaho, abseneeof rock decay in............. 26,27

India, laterite in......................25,28,29,56

Iron in residual clays ...................... 43

in Newark sandstone................... 50,51

Istrian peninsula, deposits of terra rossa in

the................................... 2»

J.

Jamaica,red solicited. ................. 28,33

James River, Virginia, analysis of the water

of.................................... 37,38

Jonesborough, N. C., rock decay near...... 13

Julien, A. A., on the red color of certain

rocks ................................ 48,54

K. -

Karst earth. (See Terra rossa.) 

Kerguelen Islands, climate and absence of

soil on ........s...................... 30,31

Kerr, "W. C., cited on rock decay........... la

Knox dolomite, chert and soil derived from

decay of....... ................... 21

and residual clay, analysis of .......24,25,40

Knoxville, Term., geological work near.... 9

L.

Lakes, color of the sediments of....... . 42,47

Land of Desolation. (See Kerguelen.)

Laterite, equivalent of, in America ........ 25

in southern Asia..................25,28,29,56

Leesburg, Va., geological work near ....... &

Lefroy, J. H., cited on soils of Bermuda.... 29-

Lesley, J. P., cited on residual clay from

Pennsylvania. .................... 39,40

Letter of transmittal...................... &

Lexington, Va., analysis of Trenton limestone and residual clays ............ 24,39,40

Liais, E., cited on rock decay in Brazil..... 28

Limestone in Alabama, decay of........... 21-24

Lookout Mountain, origin of............... i5.

M.

McKay, A. W., on the red color of certain

rocks ................. ........... 48

Madras, deposits of laterite near........... 28

Madrid, residual clays near ................ 28

Manganese in residual clays............... 43

Massachusetts, volcanic dust in ........... 50

Medlicott, H. B., and W. T. Blanford, cited

on laterite of India .................. 29

Michigan, color of Pleistocene deposits of

Lake................................. 47

Mississippi River, inorganic matter in the

water of.............................. 39

Mojave desert, prevailing color of soil on

the................................... 27

Morrisville, Ala., analysis of Knox dolomite

and residual clay from ...'......... .24,25,40>

N.

Neumayr, M., cited on red clay in Europe . 28 

Nevada, absence of rock decay in.......... 26,27

color of recent lake beds in............ 42

(596)
INDEX. 65

48

18

Page. 

Newark areas, color of soils in.............. 41

Newark sandstone, iron in................. 50,51

Newark system, the object of study -. .. 9 

nseof the name........................ 11

decay of the rocks of the.............. 15-18

analysis of decomposed trap rook 

of ..............................17,18,39,40

increased decay of the rocks towards 

thesontli ............................ 18

origin of the prevailing color of ....... 44-46

origin of the rocks of.................. 45

Newberry, J. S., on the red color of certain

rocks ................................ 52

New Found Mountains, North Carolina,

scenery of...........i..............19, PI. 2

New Jersey, origin of the red color of the

Newark rocks in ..................... 50

New Mexico, absence of rock decay in ..... 26,27

Newton, H., on the red color of certain

rocks ................................ 52,53

Nicaragua, rock decay in................... 28

North Carolina, decay of the rocks in.. ..15,16,18

hard water near trap dikes in.......... 17

analysis of decomposed trap from near 

Wadesborough....................... 39,40

Nova Scotia, origin of the red color of certain rocks in.........................

0.

Ocoee schists, general absence of decay in 

the...................................

Oregon, absence of rock decay in .......... 26,27

P.

Pennsylvania, analysis of kaolin from...... 39,40

Percival, J. S., cited on the red color of certain rocks....................... . 49

Piedmont region, decay of rocks in ........ 12-15

Playa deposits, color of.................... 42

Pleistocene deposits of Lakes Superior and

Michigan, of red color.... ......... 47

Porter, J. B., on the decay of Clinton limestone at Birmingham, Ala......... 22,23

R.

Rain-fall on the west slope of the Sierra Nevada ..................... .. ... 27

Raleigh, N. C., rock decay near............. 13

Ramsay, A. C., cited on the origin o'f the

red color of certain rocks ............ 47,54

Reade, T. M., cited on the composite solids

discharged by the Mississippi River . 39 

Red beds, origin of the color of............. 42

Red earth of Jamaica, Santo Domingo, and

the Bahamas, cited................... 28

Redneld, W. C., name of the Newark system proposed by..................... 11

Red Hills, India, deposits of later!te at.... 28

Richmond, Va., analysis of water from

JamesRiverat........ ............ 37,38

Richthofen, P. von, on the relation of climate

and rock decay....................... 32

on the origin of the red color of rocks.. 46 

cited on the color of the lake loess of

China.............................. 47

Page. 

Riggs,RB., analyses by.................13,22,24

River water, average composition of....... 38

Rogers, W. B., nse of the term " Great Appalachian Valley "by................... 9

Roth, G. von, cited on the composition of

river waters......................... 38

S.

Salisbury, R. D. (See Charaberlin, T. C.) 

Samoan Islands, climate and soil of ........ 30,31

Sandstones of the Newark system, origin of

the color of .......................... 44-46

Santo Domingo, red soil of, cited........... 28,33

Sawkins, J. G. (See Wall, G. P.) 

Sierra Nevada, rock decay on west slope of. 27 

Smith, E. A., on the decay of rocks in Alabama........................!^ 19,20,21,40

South Carolina, rock decay in.............. 14

Spain,residual clay a in..................... 28

Stoppani, A., observation in Europe cited.. 28 

Storer, F. H., cited on the relation of climate to rock decay................... 33

Stubbs, William C., cited on rock decay-.. 13,32 

Superior (Lake), Pleistocene deposits of red

color from................._........ 47

T.

Taylor, W. H., analysis of water from the

James River, Virginia................ 38

Taylorsville, Cal., color of sandstone near. 53 

Tennessee, decay of rocks in............... 18,21

Terra rosaa, equivalent of, in America..... 25

relation to clim atic conditions.......... 32

Thames River, inorganic matter in water of. 39 

Thompson, C. W., on red soil and coral of

Bermuda............................. 29

cited on the color of abyssal deposits.. 55 

Trap rock, influence on the color of associated sandstone of ..................49,50-52

Trap rocks, of the Newark system......... 16-18

Trenton limestone and residual clays,

analysis of.........................24,39,40

Trinidad, climate and rock decay in....... 31,33

Tuomey, M., cited on rock decay in South

Carolina............................. 14

on decay of trap dikes in North Carolina.................................. 17

TJ. / 

Utah, absence of rock decay in............ 26,27

V. 

Virginia, rock decay in................... 12,16,24

prevailing color of soil in .............. 27

analysis of residual clay from'.......... 39,40

Volcanic dust in Hampshire County, Mass. 50

W. 

Wadesborough, N. C., chemical character of

decomposed trap from .......... 17,18,39,40

rock decay near........................ 13,16

Wall, G. P., and J. G. Sawkins, on rock decay

in Trinidad .......................... 31

Whitaker, W., cited on earth charged with

flints in England ..................... 21*

Wills Valley, Alabama, chert left by the

decay of dolomite in ................. 21

Bull. 52-