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DEPAKTMENT O If, THE INTERIOR

BULLETIN

OF THE

UNITED STATES

GEOLOGICAL SURVEY

N"o. 38 30275

PERIDOTITE OF ELLIOTT COUNTY, KENTUCKY

WASHINGTON

GOVERNMENT PRINTING OFFICE

1887

ADVERT I SEGMENT.

[Bulletin No. 38.]

The publications of the United States Geological Survey are issued in accordance with the statute 

approved March 3,1879, which declares that 

" The publications of the Geological Survey shall consist of the annual report of operations, geological 

and economic maps illustrating the resources and classification of the lands, and reports upon general 

and economic geology and paleontology. The annual report of operations of the Geological Survey 

shall accompany the annual report of the Secretary of the Interior. All special memoirs and reports 

of said Survey shall be issued in uniform quarto series if deemed necessary by the Director, but otherwise in ordinary octavos. Three thousand copies of each shall be published for scientific exchanges 

and for sale at the price of publication; and all literary and cartographic materials received in exchange 

shall be the property of the United States and form a part of the library of the organization: And the 

money resulting from the sale of such publications shall be covered into the Treasury of the United 

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On July 7,1882, the following joint resolution, referring to all Government publications, was passed 

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" That whenever any document or'report shall be ordered printed by Congress, there shall be printed, 

in addition to the number in each case stated, the 'usual number' (1,900) of copies for binding and 

distribution among those entitled to receive them."

Except in those cases in which an extra number of any publication has been supplied to the Survey 

by special resolution of Confess or has been ordered by the Secretary of the Interior, this Office has 

no copies for gratuitous distribution.

ANNUAL REPORTS.

Of the Annual Reports there have been already published:

I. First Annual Report to the Hon. Carl Schurz, by Clarence King. I860. 8°. 79 pp. 1 map. A 

preliminary report describing plan of organization and publications.

II. Report of the Director of the United States Geological Survey for 1880-'81, by J. W. Powell. 

1882. 8°. Iv, 588 pp. 61 pi. 1 map.

in. Third Annual Report of the United States Geological Survey, 1881-! 82, by J. tF. Powell. 1883. 

8°. xviii, 564 pp. 67 pi. and maps.

IV. Fourth Annual Report of the United States Geological Survey, 1882-'83, by J. W. P,owol . 1884. 

8°. xxxii, 473 pp. 85 pi. and maps.

V. Fifth Annual Report of the United States Geological Survey, 1883-'84, by J. W. Powell. 1885. 

8°. xxxvi, 469 pp. 58 pi. and maps. 

The Sixth and Seventh Annual Reports are in press.

MONOGRAPHS. '

Of the Monographs, Nos. II, III, IV, V, VI, VII, VHI, IX, X, and XI are now published, viz:

II. Tertiary History of the Grand Canon District, with atlas, by Clarence E. Dutton, Capt. U. S. A. 

1882. 4°. xiv, 264 pp. 42 pi. and atlas of 24 sheets folio. Price $10.12.

III. Geology of the Comstock Lode and the Washoe District, with atlas, by George F. Becker. 

1882. 4°. xv, 422 pp. 7 pi. and atlas of 21 sheets folio. Price $11.

IV. Corastock Mining and Miners, by Eliot Lord. 1883. 4°. xiv, 451 pp. 3 pi. Price $1.50.

V. Copper-bearing Rocks of Lake Superior, by Roland D. Irving. 1883. 4°. xvi, 464 pp. 15=1. 

29 pi. Price $1.85.

VI. Contributions to the Knowledge of the Older Mesozoic Flora of Virginia, by "Win. M. Fontaine. 

1883. 4°. xi, 144pp. 541. 51 pi. Price $1.05.

VII. Silver-Lead Deposits of Eureka, Nevada, by Joseph S. Curtis. 1884. 4°. xiii, 200 pp. 16 pi. 

Price $1.20.

VILT. Paleontology of the Enreka District, by Charles D. "Walcott; 1884. 4°. xiii, 298 pp. 241. 

24 pi. Price $1.10.

IX. Brachiopoda and Lamellibranchiata of the Raritan Clays and G'reensand Marls of New Jersey, 

by Robert P. TVhitfield. 1885. 4°. xx, 338 pp. 35 pi. Price $1.15.

X. Dinocerata. A Monograph of an Extinct Order of Gigantic Mammals, by Othniel Charles Marsh. 

1885. 4°. xviii, 243 pp. 56 1. 56 pi. Price $2.70.

XI. Geological History of Lake Lahontan, a Quaternary Lake of Northwestern Nevada, by Israel 

Cook Russell. 1885. 4°. xiv, 288 pp. 46 pi. Price $1.75.
ADVERTISEMENT.

The following is in press, viz:

XH. Geology and Mining Industry of Leadville, with atlas, by S. F. Emmons. 1886. 4°. xxix, 

770 pp. 45 pi. and atlas of 35 sheets folio. 

The following are in preparation, viz: 

I. The Precious Metals, by Clarence King.

 Gasteropoda of the New Jersey Cretaceous and-Eocene Marls, by R. P. "Whitfleld.

 Geology of the Eureka Mining District, Nevada, with atlas, by Arnold Hague.

 Lake Bonneville, by G. K. Gilbert.

 Sauropoda, by Prof. 0. C. Marsh.

 Stegosauria, by Prof. 0. C. Marsh.

 Brontotheridae, by Prof. O. C. Marsh.

 Geology of the Quicksilver Deposits of the Pacific Slope, with atlas, by George F. Becker.

 The Penokee-Gogebic Iron-Bearing Series of North Wisconsin and Michigan, by Koland D. Irving.

 Younger Mesozoic Flora of Virginia, by William M. Fontaine.

 Description of New Fossil Plants from the Dakota Group, by Leo Leaquereux.

 Report on the Denver Coal Basin, by S. F. Emmons.

 Report on Ten-Mile Mining District, Colorado, ,by S. F. Emmons.

 Report on Silver Cliff Mining District, by S. F. Emmons.

 Flora of the Dakota Group, by J. S. Newberry.

BULLETINS.

The Bulletins of the Survey will contain such papers relating to the general purpose of its work as 

do not properly come under the heads of Annual Reports or Monographs.

Each of these Bulletins contains but one paper and is complete in itself. They are, however, numbered in a continuous series, and may be united into volumes of convenient size. To. facilitate this, 

each Bulletin has two paginations, one proper to itself and another which belongs to it as part of the 

volume.

Of this series of Bulletins Nos. 1 to 38 are already published, viz:

1. On Hypersthene-Andesite and on Triclinic Pyroxene in Augitic Rocks, by Whitman Cross, with 

a Geological Sketch of Buffalo Peaks, Colorado, by S. F. Emmons. 1883.8°. 42pp. 2 pi. Price 10 cents.

2. Gold and Silver Conversion Tables, giving the coining values of troy ounces of fine metal, etc., by 

Albert Williams, jr. 1883. 8°. 8pp. Price 5 cents.

3. On the Fossil Faunas of the Upper Devonian, along the meridian of 76° 30', from Tompkins County, 

NewTork, to Bradford County, Pennsylvania, by Henry S.Williams. 1884. 8°. 36pp. Price 5 cents.

4. On Mesozoic Fossils, by Charles A. White. 1884. 8°. 36 pp. 9 pi. Price 5 cents.

5. A Dictionary of Altitudes in the United States, compiled by Henry Gannett. 1884. 8°. 325 pp. 

Price 20 cents.

6. Elevations in the Dominion of Canada, by J. W. Spencer. 1884. 8°. 43.pp. Price 5 cents.

7. Mapoteca Geologica Americana. A catalogue of geological maps of America (North and South), 

1752-1881, by Jules Marcou and John Belknap Marcou. 1884. 8°. 184 pp. Price 10 cents.

8. On Secondary Enlargements of Mineral Fragments in Certain Rocks, by R. D. Irving and C. R. 

Van Hise. 1884. 8°. 56 pp. 6 pi. Price 10 cents.

9. Report of work done in the Washington Laboratory during the fiscal year 1883-'84. F. W. Clarke, 

chief chemist; T. M. Chatard, assistant. 1884. 8°. 40 pp. Price 5 cents.

10. On the Cambrian Faunas of North America. Preliminary studies, by Charles D. Walcott. 1884. 

8°. 74 pp. 10 pi. Price 5 cents.

11. On the Quaternary and Recent Mollusca of the Great Basin; with Descriptions of New Forms, by 

R. Ellsworth Call; introduced by a sketch of the Quaternary Lakes of the Great Basin, by G. K. Gilbert. 1884. 8°. 66 pp. 6 pi. Price 5 cents.

12. A Crystallographic Study of the Thlnolite of Lake Lahontan, by Edward S. Dana/' 1884. 8°. 

34 pp. 3 pi. Price 5 cents.

13. Boundaries of the United States and of the several States and Territories, by Henry Gannett, 

1885. 8°. 135 pp. Price 10 cents.

. 14. The Electrical and Magnetic Properties of the Iron-Carburets, by Carl Barus and Vincent 

Strouhal. 1885. 8°. 238 ppj[ Price 15 cents.

15. On the Mesozoic and Cenozoic Paleontology of California, by Charles A. White. 1885. 8°. 

33 pp. Price 5 cents.

16. On the higher Devonian Faunas of Ontario County, New York, by John M. Clarke. 1885. 8°. 

86pp. 3 pi. Price 5 cents.

17. On the Development of Crystallization in the Igneous Rocka of Washoe, Nevada, by Arnold 

Hague and Joseph P. Iddings. 1885. 8°. 44 pp. Price 5 cents.

. 18. On Marine Eocene, Fresh-water Miocene, and other Fossil Mollusca of Western North America, 

by Charles A. White. 1885. 8°. 26 pp. 3 pi. Price 5 cents.

19. Notes on the Stratigraphy of California, by George F. Becker. 1885. 8°, 28 pp. Price 5 cents.

20. Contributions to the Mineralogy ot the Rocky Mountains, by Whitman Cross and W. F. Hillebrand. 1885. 8°. 114pp. 1 pi. Price 10 cents.
ADVERTISEMENT.

21. The Lignites of the Great Sioux Keservation, by Bailey Willis. *885. 8°. 16 pp. 5 pi. Price 

5 cents.

22. On New Cretaceous Fossils from California, by Charles A. White. 1885. 8°. 25pp. 5 pi. Price 

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23. Observations on the Junction between the Eastern Sandstone and the Keweenaw Series on 

Keweenaw Point, Lake Superior, by K. D. Irving and T. C. Chamberlin. 1885. 8°. 124 pp. 17 pi. 

Price 15 cents.

24. List of Marine Mollusca, comprising the Quaternary fossils and recent forms from American 

localities between Cape Hatteras and Cape Roque, including the Bermudas, by William H. Dall. 1885. 

8°. 336 pp. Price 25 cents.

25. The Present Technical: Condition of the Steel Industry of the United States, by Phineas Barnea. 

1885. 8°. 85 pp. Price 10 cents.

26. Copper Smelting, by Henry M. Howe. 1885. 8°. 107 pp. Price 10 cents.

27. Report of work done in the division of Chemistry and Physics, mainly during the fiscal year 

1884-'85. 1886. 8°. 80pp. Price 10 cents.

28. The Gabbros and Associated Horn blende Books occurring in the neighborhood of Baltimore, Md., 

by George H. Williams. 1S86. 8°. 78pp. 4 pi. Price 10 cents.

29. On the Fresh-water Invertebrates of the North American Jurassic, by Charles A. White. 1886. 

8°. 41pp. 4 pi. Price 5 cents.

30. Second contribution to the studies on the Cambrian Faunas of North America, by Charles D. 

Walcott. 1886. 8°. 369 pp. 33 pi. Price 25 cents.

31. A systematic review of oar present knowledge of Fossil Insects, including Myriapods and Arachnids, by Samuel H. Scudder. 1886. 8°. 128 pp. Price 15 cents.

32. Lists and Analyses of the Mineral Springs of the United States; a preliminary study, by Albert 

C. Peale. 1886. 8°. 235 pp. Price 20 cents.

33. Notes on the Geology of Northern California, by Joseph S. Diller. 1886. 8°. 23pp. Price 5 cents.

34. On the relation of the Laramie Molluscan Fauna to that of the succeeding Fresh-water Eocene 

and other groups, by Charles A. White. 1886. 8°. 54 pp. 5 pi. Price 10 cents.

35. The Physical Properties of the Iron-Carburets, by Carl Barns and Vincent Strouhal. 1886. 8°. 

62 pp. Price 10 cents.

36. Subsidence of fine Solid particles in Liquids, by Carl Barus. 1887. 8°. 58 pp. Price 10 cents.

37. Types of the Laramie Flora, by Lester F. Ward. 1887. 8°. 354 pp. 57 pi. Price 25 cents.

38. Peridotite of Elliott County, Kentucky, by Joseph S. Diller. 1887. 8°. 31 pp. 1 pi. Price 5 

cents.

Numbers 1 to 6 of the Bulletins form Volume I; Numbers 7 to 14, Volume II; Numbers 15 to 23, Volume III; Numbers 24 to 30, Volume IV; Numbers 31 to 36, Volume V. Volume VI is not yet complete.

The following are in press, viz:

39. The Upper Beaches and Deltas of the Glacial Lake Agassiz, by Warren Upham.

40. Changes in River Courses in Washington Territory due to Glaciation, by Bailey Willis.

41. Fossil Faunas of the Upper Devonian the Genesee Section, by Henry S. Williams.

42. Report of work done in the division of Chemistry and Physics, mainly during the fiscal year 

1885-'86. F. W. Clarko, chief chemist.

43. On the Tertiary s.nd Cretaceous Strata of the Tuscaloosa, Tombigbee, and Alabama Rivers, by 

Eugene A. Smith and Lawrence C. Johnson. 

In preparation:

44. Historic statement respecting geologic work in Texas, by R. T. Hill.

45. The Nature and Origin of Deposits of Phosphates of Lime, by R. A. F. Penrose, jr.

46. Bibliography of North American Crustacea, by A. W. Vogdes.

 The Gabbros and associated rocks in Delaware, by F. D Chester.

 Report on Louisiana and Texas, by Lawrence C. Johnson.

STATISTICAL PAPERS.

A fourth series of publications, having special reference to the mineral resources of the United 

States, has been undertaken.

Of that series the following have been published, viz:

Mineral Resources of the United States [1882], by Albert Williams, jr. 1883. 3°. xvii, 813pp. Price 

50 cents.

Mineral Resources of the United States, 1888 and 1884, by Albert Williams, jr. 1885. 8°. xiv, 1016 

pp. Price 60 cents.

Mineral Resqurcesi of the United States, 1885. Division of Mining Statistics and Technology. 1886. 

 8°. vii, 576 pp. Price 40 cents.

Correspondence relating to the publications of the Survey, and all remittances, which must be by 

POSTAL NOTE or MOSEY ORDER, (not stamps), should be addressed

To THE DIRECTOR OF THE

UNITED STATES GEOLOGICAL SURVEY,

WASHINGTON, D. C. 

WASHINGTON, D. C.., April 15, 1887.

DEPARTMENT OF THE INTERIOR

BULLETIN

OK THK

UNITED STATES

GEOLOGICAL SURVEY

No. 38

WASHINGTON

GOVERNMENT PRINTING- OFFICE

IS S 7

J, 3(2.3>6J 

£>^%

UNITED STATES GEOLOGICAL SUEVET

J. W. POWELL, DIRECTOR

PERIDOTITE

OF

ELLIOTT COUNTY, KENTUCKY

J. S.

\^-h »4,<

WASHINGTON

GOVERNMENT PRINTING.OFFICE

1887

CONTENTS.

Introduction................................................................. 9

Distribution and mode of occurrence......................................... 9

Mineralogical composition and structure..................................... 10

Eolations and origin of the peridotite........................................ 20

Chemical composition........................................................ 24

Loose fragments of feldspathic rocks found with the peridotite............... 25

Age of the peridotite........................................................ 28

Summary.................... ....... .. .... ............ ............. 29

Index..................-.........-.......................... ............. 31

(359) 5

ILLUSTRATIONS.

Paga

PLATE I. Map of the portion of Elliott County in which the dikes occur...... 10

FIG. 1. Section of peridotite seen under the microscope ...................... 11

2. Crystal of olivine.................................................... 12

3. Original structure of peridotite seen under the microscope ............ 12

4. Corroded eristatite with border ..................................... 13

5. Biotite.............................................................. 14

6. Pyrope, sho wing border of biotite and magnetite..................... 15

7. Part of a border about a grain of pyrope, magnified 80 diameters...... 16

8. Included tnicrolites and cavities in garnet., .._................... 27

(361) 7

PERIDOTITE OF ELLIOTT COUNTY, KENTUCKY.

BY J. S. DILLEK.

INTRODUCTION.

Several years ago Prof. A. E. Crandall, of the Geological Survey of 

Kentucky, discovered dikes of an interesting eruptive rock between 

Isom's and Oritche's Creeks, near Fielden post office, 6 miles southwest 

of Willard, in Elliott County, Kentucky. The position of these dikes 

is shown upon two of the geological maps of Eastern Kentucky. Both 

maps were prepared under the supervision of John E. Procter, the director of the Kentucky Geological Survey, by Professor Crandall and 

J. B. Hoeing. One, on a scale of about 4 miles to an inch, is designed to 

show the relation of the conglomerate uplifts and the dikes; the other, 

on a scale of 2 miles to an inch, gives the areal distribution of the dikes, 

the Coal Measures, and the conglomerate in Elliott County. In a vertical section on the same sheet the relations of these terranes are illustrated.

A chemical analysis of the dike rock was made by Messrs. A. M. Peter 

and J. H. Kastle, in the laboratory of the Geological Survey of Kentucky. Samples of the same material were sent to the United States 

Geological Survey for microscopic examination. It was found to be a 

peridotite, and a brief notice of its occurrence was published in Science, 

January 23, 1885, page 65.

At the request of Mr. Procter and with the approval of Capt. C. E. 

Button and the Director of the United States Geological Survey, I 

joined Professor Crandall in an excursion to the dikes to collect a complete series of specimens for petrographic investigation.

DISTRIBUTION AND MODE OF OCCURRENCE.

The accompanying map, Plate I, was prepared by enlarging a small 

portion of the map of Elliott County and introducing the additional 

data obtained during our late excursion.

At my request, Professor Crandall, who has visited the region a 

number of times, kindly furnished the following field notes:

This dike represents an eruption of very limited extent laterally, being found only 

in a small part of the valley of the Little Fork of the Little Sandy River. From its 

limited range, and also from the readiness with which the rock of which it is composed disintegrates, it does not appear as a noticeable factor in the topography of the

(363) 9
10 ELLIOTT COUNTY PERIDOTITE. [BULL. 38.

region, and it is with some difficulty that it can be traced beyond the exposures 

which mark a few points along its surface prolongation. It appears to extend in two 

diverging lines from Critche's Creek into the valley of Isom's Creek, "with several 

minor offshoots of undetermined but doubtless limited extent, possibly no more 

than -wedge-like projections from the main dike between the strata of the Coal 

Measures which make up the whole height of the hills of this region. The whole 

length of the dike in its greatest surface extension appears to be less than a mile, 

with a width of from a few feet to fifty or more, as indie ated by one exposure near 

Isom's mill, though the slight local disturbance of the including rocks and the inconsiderable metamorphic action, as well as the limited area, indicate no great mass of 

the intrusive rock. These considerations and some of the conditions noted at Isom's 

mill suggest the possibility that the exposure there shows a local lateral expansion, rather than the width of the dike. All the rocks of this part of the coal field, 

including the beds up to coal seven (the Coalton coal of Kentucky, the Sheridan and 

Nelsonville of Ohio), are cut by both arms of the dike.

Although there are but three localities where the peridotite is exposed, its areal distribution, as indicated upon the accompanying map 

(Plate I), can be made out with a high degree of probability by the 

occurrence of numerous small fragments of ilmenite and pyrope in the 

soil resulting from its decomposition.

MINERALOaiCAL COMPOSITION AND STRUCTURE.

The best and freshest specimens of peridotite were collected at locality marked 1 upon the map, where the specimens were prepared for the 

educational series. It is a compact, dark greenish rock, with a specific 

gravity of 2.781. In it are embedded many grains of yellowish olivine, 

uniformly distributed throughout the mass. Earely it is fine granular 

and dense, like many darker colored basalts, but generally the grains of 

which it is composed are medium sized. Occasionally the olivine grains 

disappear and the deep green serpentine pervades the whole mass. 

Besides the oliviue and serpentine, which together form nearly 75 per 

cent, of the rock, there are other minerals which appear in the hand 

specimen. Most important among these are pyrope and ilmenite, the 

latter appearing in the form of irregular grains which sometimes attain 

a diameter of nearly 2 centimeters. A few scales of biotite may be 

observed. Near the exposed surface the rock becomes yellowish, due 

to the oxidation of the iron, and softens so that it readily disintegrates. 

The garnet and much of the ilmenite withstand the atmospheric influences and are found quite fresh and abundant in the sand resulting 

from the disintegration of the peridotite.

The specimens from localities 1 and 2, the exposures of the eastern 

dike, are free from included fragments of the rocks through which the 

peridotite has been extravasated; but those from locality 3, in the western dike near Isom's mill, are full of fragments of shale, which have 

been greatly indurated and metamorphosed in the operation.

The following table is based directly upon estimates made under the 

microscope of the areal distribution of the various minerals in the

(364)
U. 8. GEOLOGICAL SURVEY BULLETIN NO. 33 PL. I

(Exposed Peridotite, %jj$ Soil containing Pyrope and Ilmenite, 

Scale

Loose fragments of 

Feldspathic rocks,

I Mile

MAP OF THE PORTION OF ELLIOTT COUNTY IN WHICH THE DIKES OCCUR.
DILLKR.] MINERALOGICAL COMPOSITION AND STRUCTURE. 11

freshest portions of the sections from locality 1, where the peridotite is 

less altered than at any of the other exposures:

Primary minerals.

Per cent.

1

1

8

2.2

Secondary minerals.

Per cent.

on T

14

1.1

It is not claimed, of course, that this table represents with a high 

degree of accuracy the mineralogical composition of the rock, yet it 

closely approximates the real proportions in the sections studied. The 

table clearly indicates that originally at least 80 per cent, of the rock 

was olivine and that ultimately it will be nearly all serpentine or, 

perhaps, in some places dolomite with a small proportion of magnetite, ilmenite, garnet, and octahedrite.

FIG. 1. Section of peridotite seen under the microscope.

The general structure of the rock is illustrated in Fig. 1, which shows 

the remaining grains of olivine inclosed in a network of serpentine 

with other products of alteration. The high proportion of olivine in 

the rock places it among those peridotites which are generally designated dunites, but the presence of some enstatite shows its relationship to another member of the same family.

(365)
12 ELLIOTT COUNTY PEKIUOTITE. [BULL. 38.

The olivine grains are generally irregular in form, varying from 0.1 

to 1.5 millimeters in diameter, and are penetrated by many fissures. 

Occasionally, however, they are bounded by sharply defined crystallographic planes, a feature which is unusual for the olivine in peridotites. 

It occurs in .the form, which is common in basaltic lavas, ot a short 

prism terminated by brachydoines without the base, as in Fig. 2. The

FIG. 2. Crystal of olivine. FIG. 3. Original structure of peridotite seen under 

the microscope.

original structure of the rock is nearly obliterated by recent alteration ; but at one point, which is represented in Fig. 3, the manner in 

which the coarse grains of olivine fit together is plainly discernible. 

Barely the aggregating grains are very small, and, although optically 

distinct, each fits into the irregularities of the other so as to produce a 

fine granular structure similar to that of the dunite of North Carolina. 

Under the microscope, especially when the dunite is slightly altered, 

it holds such a superficial resemblance to a stratified rock that A. A. 

Julien1 regarded it as an accumulation of olivine sand derived from an 

earlier eruptive mass ; but Dr. M. E. Wadsworth2 has shown that in 

all probability it is eruptive in its present position. The presence of a 

similar structure in the peridotite of Kentucky, the eruptive origin of 

which cannot be reasonably questioned, lends strong support to Dr. 

Wads worth's conclusions.

The alteration ot the olivine to serpentine takes place rapidly in the 

cross-fractures approximately parallel to the base, but very slowly 

along the numerous minute fissures in the prism zone. Cleavage parallel to the brachypinacoid is scarcely discernible.

The olivine contains numerous small inclusions, some of which are of 

a liquid containing a movable bubble. They are arranged in more or 

less regular planes, often but not always approximately parallel to the

Dunyte Beds of North Carolina. Proc. Bost. Soo. Nat. Hist., Vol. XXII, 

p. 141. 

*Olivine Rocks of North Carolina. Science, Vol. Ill, p. 486, Apr. 18, 1884.

(360)
DILLBR.] MINERALOGICAL COMPOSITION AND STRUCTURE. 13

base. Besides these inclusions, there are other small yellowish-brown 

or black ones scattered like dust, but rarely so abundant as to interrupt 

the transparency of the oliviue. Occasionally they accumulate in bands 

across the grains or around their borders, as described by J. W. Judd1 

and others, producing dark cloudings which remain after the olivine 

has been replaced by serpentine. The olivine was observed to envelop 

scales of biotite, indicating that the latter belong to an earlier stage of 

crystallization than the olivine.

In the process of alteration the olivine is transformed, into serpentine 

 with the secretion of magnetite. Among the secondary products there 

is much dolomite, which appears to result from the transformation of 

the olivine. The abundance of the carbonate present suggests that 

the olivine might contain a considerable percentage of lime, and to determine this it was prepared for chemical analysis. By means of the 

Sonstadt solution, with a specific gravity of 2.9, the magnetite, biotite, 

ilmenite, enstatite, octahedrite, and olivine were separated from the 

serpentine and other secondary products, With a magnet the magnetite was then removed, and by passing the powder over paper the 

mica was separated from the other minerals. The mixture of olivine, 

ilmenite, enstatite, octahedrite, and garnet was then put into the Klein 

solution and evaporated until crystallization began. At this point the 

olivine and a trace of enstatite were lifted by the solution and, by decantation, separated from the other minerals. This operation was repeated many times, and finally, picking out all foreign matter under the 

microscope, the olivine was obtained remarkably pure for chemical 

analysis. Its specific gravity, determined by using a picnometer, is 

3.377. The results of the chemical analysis of the olivine by T. M. 

Chatard, in the chemical laboratory of the United States Geological 

Survey, are given in the table of analyses, page 24. It will be noticed 

that the percentage of lime and alkalies present is unusually large.

Pyroxene plays so small a part among the minerals of this rock that 

it cannot be considered an essential 

constituent. In the form of irregularly 

corroded grains, such as is represented 

in Fig. 4, it is distributed throughout 

the mass with approximate uniformity, 

but it constitutes not more than 1 per 

cent, of the whole. The cleavage is 

nearly rectangular and the extinction 

in prismatic sections parallel, indicating with a high degree of probability 

that the pyroxene is rhombic. It is

,. . , . . FIG. 4. Corroded enstatite with border. generally transparent, with a sprinkling of fine dark grains, and is surrounded by a clouded border con1 On the Tertiary and Older Peridotites of Scotland. Quarterly Journal of the 

Geological Society, August, 1885, p. 354.

(367)
14 o ELLIOTT COUNTY PERIDOTITE. luuLL.38.

forming to the embayed contour. This border is irregular in structure 

and composition, but is almost always present. Where most prominent 

it is formed of acicular crystals radiating from the enstatite, but generally it is composed of translucent grains of pyroxene rendered somewhat clouded, apparently by the secretion of ferritic matter. The fibrous 

mineral is transparent, with strong double refraction and small angle 

of extinction, indicating that it is hornblende.

The embayments of the irregular enstatite sometimes contain olivine, 

demonstrating that, the pyroxene is an earlier product of crystallization 

than the olivine and owes its border, at least in part, to the subsequent 

corrosive action of the magma.

The mica is dark colored, strongly dichroic, with a very small optic 

axial angle in the plane of the principal ray of the radial figure (Schlagfigur) produced by puncturing a thin plate of the mica with a sharp 

needle. It doubtless belongs to the biotite series and is sparingly distributed throughout the rock. Figure 5 represents a 

. ,*\. cross section of a somewhat uncommon scale of brown 

biotite made up of laminae differing from one another 

in pleochroism. The folise forming the top and the 

base of the scale, the shaded portions in Fig. 5, are 

more deeply colored and strongly dichroic than the 

light brown portion in the middle. All portions are 

optically continuous and surrounded by a prominent 

border composed of colorless mica and oxide of iron. 

The mica of the border is continuous with the other, 

and evidently owes its loss of color to leaching out the 

FIG 5 Biotite oxide'of iron. With the exception of fine ferritic dust 

irregularly scattered throughout the scales of mica it 

is generally free from inclusions. One scale, however, has prominent 

deep brown isotropic inclusions which lie in the basal plane. They 

look very like basaltic hornblende in ordinary transmitted light, b.ut 

the entire absence of double refraction and consequent properties clearly 

demonstrates that if the substance is crystalline in structure it must 

belong to the isometric system. It is perhaps significant that the axes 

of greatest extension in the inclusions are approximately parallel to 

three sets of sharp fissures which apparently correspond to the rays 

of the peculiar figure developed by pressure, the so-called Druckfigur. 

The general appearance of the biotite conveys the impression that it has 

undergone conditions detrimental to its existence and must belong to 

the earliest products of crystallization. Of this we have convincing 

evidence in its relations to other minerals, for biotite is frequently 

included in olivine. Barely the biotite is surrounded by an irregular 

secondary border composed of magnetite and biotite differing widely in 

pleochroism from the biotite within the border. The biotite of the grain 

and its border are optically continuous, but, while the pleochroism of the

(368)
DILLBR.] MINERALOGICAL COMPOSITION AND STRUCTURE. 15

former- ranges from almost colorless to light brownish yellow, that of 

the latter in corresponding positions is orange-yellow and green.

The relation of the biotite to the garnet is of especial interest and 

will be noted in discussing the composition of that peculiar envelope in 

which the pyrope is inclosed. It is evident, however, that the biotite 

upon the periphery and in the fissures of the garnet is of secondary 

origin.

Pyrope cannot be considered one of the essential minerals in this rock, 

yet it is among the most prominent. It occurs in spherical and ellipsoidal 

grains varying from 1 millimeter to more than a dozen millimeters in 

diameter. They are found abundantly along the line of the dike in the 

soil resulting from its disintegration. The small, clear, deep red grains 

have a specific gravity of 3.673 and are locally regarded as rubies of 

problematical value, but the paler red, much fractured fragments of 

larger size have attracted little attention.

The most interesting feature of the pyrope is prominent under the 

microscope, where it is seen to be surrounded by a border of radial fibers 

analogous to that described by Fr. Becke1 and A. Schrauf,2 and later critically examined by A. v. Lasaulx.3 Tbe general character of the border 

is represented in Fig. 6. It is composed of two essentially different substances, both of which are always present, 

although varying much in proportions. 

First of these may be mentioned a dark 

.powder, which is frequently so abundant 

as to render the border opaque. It occurs 

most abundantly in the; outer portion of 

the border and is chielly, if not wholly, 

magnetite; for when carefully detached by 

a sharp needle from an uncovered section FIG. e. Pyrope, showing border of

... f , . , , , ,. -T,, biotite and magnetite. it is found to be strongly magnetic. The

second usually inuer su.bstance of the ring is of a grayish or reddish 

brown color and is generally fibrous in structure. Schrauf studied the 

fibrous substance enveloping the garnets in the serpentine of Kremze, 

Bohemia, and named it kelyphite. The investigations of Lasaulx have 

shown that in some cases the border instead of being a single mineral is a 

mixture of several minerals, chiefly of the pyroxene and amphibole 

groups. In the example under consideration its composition appears to 

be exceptional. Although it is commonly made up of closely compacted,

1 Tscherrnak's Mittheilungen, iv, 1881, pp. 189, 285.

2 Beitriige zur Kenntniss des Associations-kreises der Magnesia-Silikate. Zeitschrift 

fur Krystallographie, 1882, VI., pp. 3:21-388 ; also Ueber Kelyphite. Neues Jahrbuch, 

1334, Bd. II, p. 21.

3 Ueber Umrindungen von Granat. Sifczungsberichte der niederrhein. Gesellschaffr, 

Bonn, 1882, Juli 3; Verhandluugen des nat urhistorischen Vereins der preussischen 

Rheinlande und Westfalers. Neunuuddreissigster Jahrgang, zweite Hiilfte, Bonn, 

1882, p. 114.

(369)
16 ELLIOTT COUNTY PERIDOTITE. [BULL. 38.

very fine, parallel fibers perpendicular to the outer surface of the garnet, 

it frequently appears as an irregular, non-fibrous fringe upon the inner 

side of the border, or even completely inclosed within the garnet, where 

it is usually of a deep brown color. Generally it is distinctly doubly 

refracting, and when finely fibrous is sometimes strongly colored red and 

green between crossed nicols. The non-fibrous form of the substance, 

although deeply colored, is isotropic and consequently not dichroic, but 

when fibrous the absorption parallel to tbe fibers is occasionally almost 

complete. On account of the fineness of the fibers and the density of 

their aggregation it is not possible to determine the angle of extinction 

with great precision; nevertheless if the extinction is not parallel the 

angle is very small indeed. Although many of these borders have been 

studied about the pyrope in the peridotite from Kentucky, I have not 

been able to discover convincing evidence of the presence of either 

pyroxene or hornblende; on the contrary, the evidence clearly indicates 

that the mineral belongs to the mica group. This conclusion is completely demonstrated by a border, part of which is represented in Fig. 7.

FIG. 7. Part of a border about a grain of pyrope, magnified 80 diameters.

In this case, although the border is not so prominently marked about 

the whole circumference of the garnet (5 millimeters in diameter) as that 

represented in Fig. 6, yet there are narrow places along the border 

where it is distinctly fibrous and grades directly into that represented 

in Fig. 7 in such a way as to show that both are of the same substance. 

The uniaxial, negative, strongly dichroio foliated mineral numbered 2

'(370)
DILLER.] MINERALOGICAL COMPOSITION AND STEUCTUEE. 17

in Fig. 7 is undoubtedly biotite. It extends far into the garnet along 

fissures and contains besides magnetite small triangular and quadratic 

sections as well as Irregular grains of a yellowish brown isotropic mineral, which in all probability is picotite. The first sight suggests that 

this deep brown mineral is hornblende, but the absence of all pleochroic 

phenomena and its regular octahedral form clearly indicate that it 

cannot belong to the amphibole group. One small pseudomorph after 

garnet deserves special mention, in that the whole of the middle portion 

is composed of picotite, which is surrounded by a broad border of magnetite. In the majority of cases, especially where the border is fibrous, 

the fibers are in direct contact with the clear garnet, but in the section 

of which Fig. 7 represents a part, where the biotite and picotite are 

much better developed, the garnet near the border and along fissures 

is clouded. Besides the biotite and picotite within the compass of the 

garnet's border, there are traces of calcite and a clear colorless mineral, 

which, on account of its strong double refraction and the absence of 

cleavage, is regarded as quartz. It is interesting to note that the quartz 

almost always occurs in immediate contact with the picotite.

That the shell frequently found about the garnets in peridotitic rocks 

is composed in most cases essentially of minerals belonging to the pyroxene and amphibole groups has been demonstrated by a number of 

observers, but as far as I am aware the occurrence of biotite in this 

connection is here noted for the first time.

It is evident, from the facts represented in Figs. 6 and 7, as already 

suggested by Lasaulx and Kosenbusch,1 that the pyrogenic origin of 

the shell of iron-inagnesian silicates frequently enveloping the garnet 

is generally untenable. The manner in which the enveloping substance 

is sometimes included in the garnet and penetrates the garnet along 

fissures clearly demonstrates its secondary origin.

The pyrope, from Kentucky, was carefully analyzed by T. M. Chatard, 

with the results given in the table of analyses, page 24. It was impracticable to obtain sufficient of the border for chemical examination^ 

The position of the pyrope in the series denoting the order of crystallization is between enstatite, a serpeutiuous pseudomorph of which it 

includes, and olivine. Its relation to the primary biotite is not easily 

determined, from the fact that where the two minerals are found together the biotite is always a secondary product.

Hinenite is a common and uniformly distributed constituent of the 

Kentucky peridotite. It is plainly visible in the freshly fractured rock, 

where it appears in the form of brilliant black grains, varying in size 

from 1 millimeter to 15 millimeters in diameter. Although subject 

to considerable alteration it frequently withstands meteoric iuflu1 H. Eosenbosch: Mikroskopische Physiographic cler petrographisch wichtigen 

Miiieralien. Zweite ganzlich umgearbeitete Auflage, 1885, p. 269.

Bull. 38 2 (371)
18 ELLIOTT COUNTY PERIDOTITE. [BULL.38,

ences with remarkable persistence, appearing abundantly with the garnet in the soil resulting from the disintegration of the peridotite. It is 

only by means of the ilmenite and pyrope in the soil, as indicated upon 

the map, that the limits of the dikes can be approximately determined. 

The ilmeuite is readily distinguished from the magnetite, even under 

the microscope in reflected light, by the brilliant luster of portions of its 

pitted surface. It has always been observed in large grains and not in 

the form of fine, spongy particles like magnetite. Under the microscope 

the ilmenite is frequently seen surrounded, penetrated, and even completely replaced by a mixed group of yellowish and black grains resulting from its alteration. The black opaque grains are magnetite and 

the yellowish ones probably octahedrite. The specific gravity of the 

ilmenite is 4.453 and a chemical analysis of it is given in the table, 

page 24.

Near the southern end of the eastern dike, at a point indicated upon 

the map, is a prehistoric embankment which appears to have been the 

foundation for works to smelt the peridotite, probably on account of the 

supposed value of the bright ilmenite it contains.

Magnetite is abundantly distributed throughout the whole rock. It 

rarely occurs in the form of well developed octahedrons, but appears generally in irregular, spongy grains a small fraction of a millimeter in diameter. The magnetite results chiefly from the alteration of the olivine 

and ilmenite, and is therefore rarely, if ever, observed as veritable inclusions in the primary minerals.

The particles picked out of the rock powder by the magnet were 

treated to an acidulated solution of sulphate of copper in water, and 

after their removal examination under the microscope showed that many 

of the grains were coated with copper, indicating that some of the iron 

was present in the peridotite in a native state.

Abundantly scattered among the other secondary products in the 

serpentinous network enveloping the remnants of olivine are yellowish 

clouded grains ranging in size from .004 to .06 millimeters in diameter. 

The intensity of the yellowish color varies considerably, with a strong 

inclination towards brown. Its index of refraction is very high, causing 

it to rise above the neighboring minerals, but its low grade of trauslucency scarcely more than allows the observer to discover that the mineral is distinctly doubly refracting without determining certainly its degree. The relation of this mineral to the ilraenite clearly indicates that 

it results from the alteration of the latter and at once suggests that it is 

a mineral with much titanium, probably titanite or one of the forms of 

titanic oxide. This is clearly demonstrated by its chemical reactions. 

With a very sharp steel point a number of these grains were removed 

from an uncovered section. In the same way a small particle of ilmenite 

about half replaced by yellow grains adhering to it was isolated. In 

both cases the material was dissolved in fused KHSO4 , and when the 

product was moistened with a solution of H2O2 it turned distinctly yellow, indicating the presence of titanium. The grains are compact and

(372)
DILLEK.] MINERALOGICAL COMPOSITION AND STRUCTURE. 10X

generally spherical, or at most not more than twice as long as thick. 

Not infrequently on<e discovers bounding planes to these grains in the 

sections that are straight and sharply defined, indicating crystallographic" 

form. Such cases are generally accompanied by a higher degree of transparency and are triangular, square, or diamond shaped. When diamondshaped the grains are most strongly doubly refracting and extinc-' 

tion takes place parallel to the longest diagonal. No trace of cleavage1 

could be discovered, nor could the system of crystallization be determined with certainty, but the facts mentioned render it highly probable that the mineral is octahedrite. The occurrence of octahedrite as 

an alteration product of ilmenite was observed by the author several 

years ago in "Schalstein" from Hof in the Fichtelgebirge, Germany.1 

Cohen and Eosenbusch,8 had previously called attention to the same 

phenomenon in other localities.

Under the microscope the rock is seen to contain an abundance of 

carbonate irregularly distributed among the secondary minerals. It is 

plainly a product of alteration, chiefly of the olivine. It is not affected 

by warm acetic acid, but effervesces vigorously in ordinary hydrochloric 

acid. After the calcium has been removed from the solution sodium 

phosphate yields an abundant crystalline precipitate, showing the presence of magnesia and demonstrating that the carbonate is dolomite. It 

rarely accumulates in nodules as large as a hazel nut and only at points 

where the rock is highly altered. The high percentage of lime and carbonic acid present in the peridotite, as shown by chemical analysis No. 

4, in the table, page 24, indicates that there is about 14 per cent, of dolomite present and that the carbonate of lime largely predominates in its 

composition. In some cases, as noted by Dr. M. E. Wads worth3 and 

Prof. E. D. Irving,4 peridotite is almost completely replaced by dolomite resulting from its alteration.

Next to olivine, serpentine is the most important mineral of the rock, 

and it occurs in two forms: first in the form of small green scales, 

which, with dolomite, magnetite, ilmenite, and octahedrite, compose the 

network in which the remaining olivine is inclosed ; frequently, however, the olivine has entirely disappeared, and its place in the meshes is 

represented by yellowish serpentine, quite unlike the first in its color 

and inclusions. The first form is bright green of varying intensity, but 

rarely pleochroic, and it has weak double refraction, yielding between 

crossed nicols a peculiar bluish aggregate polarization. Its appearance 

under the microscope is like that of chlorite, but, when isolated and 

treated with sulphuric acid and csesium chloride, it did not show the 

presence of alumina.

1 Anatas ala Umwandlungsproduct von Titanit in Biotitamphibolgranit der Troas. 

Neues Jalirbuch, VoL I, 1883, p. 187.

2 H. Rosenbiisch: Mikroskopische Physiographic der petrographisch wichtigeu 

Mineralien. Band IT, p. 336; also, Zweite Auflage, Baud I, p. 332.

3 Lithological studies: Memoirs of the Museum of Comparative Zoology, Cambridge, Mass., Vol. XI, Part I, p. 139.

4 Fifth Annual Report United States Geological Survey, 1883-'34, p. 217.

(373)
-20 ELLIOTT COUNTY PERIDOTITE. [BULL. 38.

Strongly contrasted with the green foliated serpentine is the yellowish 

fibrous form which with dolomite fills the meshes. It is often distinctly 

fibrous, and sometimes between the fibers are small radial aggregates 

which show a distinct cross between opposed nicols. The fibers are 

^sometimes distinctly dichroic; the ray oscillating parallel to the longest 

axis is yellow and perpendicular to it pale greenish, but generally it is 

not perceptibly dichroic. This form of serpentine, although free from 

the larger inclusions so common in the other, contains great numbers of 

^sma^ black grains not more than .002 of a millimeter in diameter. These 

black grains are probably the magnetite secreted in a very fine form in 

the process of serpentinization, for this serpentine is slightly magnetic.

RELATIONS AND ORIGIN OF THE PERIDOTITE.

The relation of the peridotite to the carboniferous sandstones and 

shales is of paramount importance in determining its age and origin. 

Although it has been repeatedly spoken of as a dike the evidence has not 

yet been fully presented to establish its eruptive character. Concerning the relation of the peridotite to its associated rocks only two 

hypotheses are worthy of consideration: (1) the peridotite may be 

older than the carboniferous strata and may have formed on the floor 

of the sea a peak about which the horizontal strata were deposited; 

(2) the peridotite may have been erupted through the carboniferous 

strata. If the first hypothesis is correct we would expect to find the 

adjacent sandstone composed largely of detritus derived from the peridotite and to exhibit no evidence of contact metamorphism. On the 

other hand, if the second hypothesis is true, there would not necessarily 

be a correspondence in the composition of the neighboring rocks, and 

under favorable conditions the sedimentary deposits would be metamorphosed near their contact with the eruptive.

The rocks ot the neighborhood are so disintegrated and covered with 

soil that notwithstanding our careful search we were unable to discover 

an exposure of the junction between the two rocks. Nevertheless sufficient evidence has been collected to definitely settle the problem under 

consideration. Very near an outcrop of the peridotite at locality 1 occurs a calcareous sandstone of which mineralogical and chemical an* 

alyses have been made. It is composed of quartz with a smaller proportion of triclinic feldspar, bent scales of muscovite, and biotite, all of 

which are cemented by carbonate of lime. The quartz grains are distinctly subangular and not infrequently contain minute needles of 

rutile. The sandstone is conspicuously unlike the adjacent peridotite 

in its composition and clearly indicates that the peridotite was not in 

its present position at the time the sandstone was deposited. This difference is further emphasized by the chemical analysis, No. 7, page 24. 

When it is compared with the analysis of the peridotite (No. 4) from 

the same locality the dissimilarity is so prominent as to dispel at once 

the thought that they may be genetically connected.

This discordance in the composition of the two rocks stimulated the

(374)
DILLER.] RELATIONS AND ORIGIN. 21

!

hope of discovering evidence of contact metamorphism, and in this we 

were not disappointed, for at locality 3 hardened shale was found near 

the peridotite under such circumstances that its induration is certainly 

attributable to the influence of the eruptive mass. The effects produced 

by the peridotite upon the adjacent sedimentary rocks may be considered first and subsequently those experienced by the peridotite itself 

near the contact, For convenience the shale may be regarded as made 

up of two classes of constituents, (1) the grains of sand and (2) the matrix or cement in which they are embedded. Among about a dozen 

specimens of the shale examined the relative proportions of the sand 

grains and cement vary greatly. In one case the former predominates, 

so that the rock may be regarded as a fine-grained sandstone, but generally the earthy cement is in excess and frequently forms almost the 

whole mass. Some of the clear grains are quartz, but most of them are 

of orthoclase, microcline, or plagioclase- feldspar. The matrix varies 

greatly, consisting chiefly where least altered of a heterogeneous clayey 

substance containing a multitude of microlites,1 numerous small scales 

of mica, and particles of black organic pigment with a trace of magnetite. 

The metamorphic influence of the peridotite is clearly traceable in the 

distribution of the pigment and the development of a crystalline structure in the cement. The latter becomes more and more micaceous in 

character as the metamorphism increases, and the parallel arrangement 

of the folise renders the rock more-easily split, sometimes even fissile in 

one direction. The distribution of the pigment is generally uniform 

throughout the mass, but in a portion of one of the sections it is clearly 

aggregated into groups, giving the section a mottled appearance, and 

approaches in character the so-called Knotenthonschiefer so admirably 

investigated^ by Kosenbusch.2 The name spilosite has been used to 

designate such rocks in the-contact zone about basic eruptive masses. 

The dark spots (Knoten) are not visible in the hand specimens, but may 

be plainly seen in the section and appear to be completely isotropic. 

The lighter colored areas among these show between crossed nicols 

doubly refracting grains, which are chiefly mica associated with feldspar. Chemical, analysis No. 9 was made of a fragment of indurated 

shale in which the microscopic spots were most distinctly observed. 

Analysis No. 10 is of a fragment of shale included in the peridotite. 

The size and abundance of the mica scales in the altered shale is in a 

general way proportional to the intensity of the metamorphic influence. 

A person is frequently surprised, however, to find small fragments of 

shale, less than a centimeter in diameter, completely enveloped by the 

peridotite and yet not extremely metamorphosed. In many cases the 

small fragments are almost completely altered to micaceous minerals,

1 These inicrolites correspond exactly to those so frequently observed in clay-slate 

and in a number of cases have been demonstrated to be rutile. H. Roseiibusch: 

Mikroskopische Physiographie der petrographisch wichtigen Mineralieu. Zweite 

Auflage, p. 304.

2 Die Steiger Schiefer und ihre Contactzone an dem Granititen von Barr-Audlau 

und Hohwald.

(375)
22 ELLIOTT COUNTY PERIDOTITE. [BULL. 38.

which appear to be of several sorts. A portion is completely colorless and when examined in converging light between crossed nicols 

is found to be distinctly biaxial, but the hyperbolae when farthest apart 

do not quite reach the outer limit of the field of vision. It is strongly 

doubly refracting, with the peculiar sheen commonly observed in muscovite. The other mica is more or less distinctly colored, being greenish 

or yellowish bordering upon brown, and is distinctly dichroic light to 

dark yellowish green. It occurs in irregular scales and fibers, with 

strong double refraction, and appears to be nearly or altogether uniaxial. The colorless mica is frequently continuous with that which contains considerable coloring matter, and I have frequently been in doubt 

as to the presence of more than one kind of mica.

The included fragments of shale are always surrounded by a border 

of colorless mica whose scales are intricately intermingled. Frequently, 

although not generally, the folise have their greatest dimension at right 

angles to the surface of the inclusion. This border varies in width, but 

is usually about 3 millimeters in thickness and composed almost exclusively of well developed irregular scales of colorless mica. The same 

mineral is distributed quite abundantly in the enveloped fragment. 

It appears also sparingly scattered for a short distance away upon the 

outside of the border among the serpentine and other alteration products of the peridotite. The brownish colored mica, which is so common 

in the altered shale adjacent to the peridotite, appears very different 

in the included fragments, where a higher degree of alteration has taken 

place. It here appears to be a gray, clouded, translucent mass, which, 

between crossed uicols, is seen to be made up of scales of mica. This 

advanced stage of inetamorphism in the included fragments is accompanied by the appearance of very interesting bodies which have not 

been definitely determined. They are pale yellowish in color, translucent to almost transparent, and perfectly isotropic. The diameter of 

these little balls is generally about .02 of a millimeter and they are remarkably uniform in size and shape. In general appearance they closely 

resemble the small translucent grains of octahedrite in the adjacent 

peridotite, but they cannot be octahedrite, for they are soluble in hydrochloric acid. When a flake of mica containing them is heated to a 

bright red heat they become less translucent and somewhat more earthy 

in appearance, but the change is not prominent. In the small fragments the globules are usually numerous, scattered throughout the 

scales of clouded mica, but most abundant and less regular in form 

near the border of the inclusion, where they sometimes produce a quite 

distinct band just inside the one of colorless mica. In the fragments 

where this peculiar isotropic substance is most abundant there is but 

little well developed mica. Traces of other unimportant minerals occur 

under such circumstances as to render their determination a matter of 

great difficulty. Earely among the scales of clear mica in the border 

which always surrounds included fragments of shale, may be observed 

elongated particles of a deep brown mineral, which in ordinary trans-

(376)
DIIXEB.J RELATIONS AND ORIGIN. 23

nritted light resembles hornblende, but is not pleochroic, has weak 

double refraction and an extinction angle of about 37 degrees. The 

recent discovery that the Kimberley and other diamond mines of South 

. Africa are upon volcanic necks of peridotite penetrating carbonaceous 

shale1 attaches much interest to the peridotite of Kentucky, where similar geologic relations exist. Diamonds have not yet been discovered 

in Kentucky. The shale in tffe immediate vicinity of the dikes does.not 

appear to be sufficiently rich in carbonaceous matter to excite much enthusiasm.2

An eiidomorphic effect experienced by the peridotite near its contact 

with the sedimentary rocks is apparently discernible in a structure 

which may be regarded as variolitic in character. The peridotite at 

this point contains many fragments of included shale, but in the hand 

specimens one sees nothing resembling a variolite. In a few of the thin

 sections, however, here and there among the olivine and its alteration 

products may be observed light brown, translucent, homogeneous, compact bodies similar in general appearance to the isolated sphserolites 

which sometimes occur in fresh andesitic rocks. Lighter colored veinlets run through them and between crossed nicols they are seen to be 

radially fibrous and show a distinct but not sharply defined black cross. 

'The quadrants are rather intensely but not brilliantly red, yellow, or 

green, with a peculiar fuzzy appearance. These varioles are seen only 

in sections containing inclusions of shale and appear to be most abundant in their neighborhood; but, on the other hand, small included 

fragments of shale are frequently observed without any such structure 

near them.

The facts which indicate the relation of the peridotite to the adjacent 

carboniferous strata may be briefly recapitulated. In mineralogical 

.and chemical composition the two rocks are very unlike. The carboniferous shales near their junction with the peridotite are greatly indurated by the development of a crystalline structure, which as it 

augments obliterates the sedimentary character and gives rise to a 

schistose arrangement of the particles. Fragments of shale of various 

sizes are included in the peridotite and have been greatly metamorphosed. On the other hand, the peridotite near its junction with the 

sedimentary rocks, owing to their influence upon it, has locally developed a variolitic structure such as has been not infrequently observed 

in diabases and. other eruptive rocks near their contact with older formations. These facts demonstrate beyond a doubt that the peridotite 

is a truly eruptive rock which has been forced up through the carboniferous strata. Peridotites are common rocks, but they are almost 

always associated with others of a highly crystalline character in regions 

of great disturbance, and their origin cannot be clearly demonstrated. 

By many authors they are regarded as eruptive, but by others they are

 considered to belong to sedimentary formations. In one of the very

1 H. Carvill Lewis: The Genesis of the Diamond, Science,. Yol. VIII, p. 345.

2 The Genesis of tho Diamond, Science, Vol. VIII, p. 392, October 29, 1886.

(377)
24 ELLIOTT COUNTY PEKIDOTITE. [BULL. 38.

latest works on lithology1 they are included among "katogene" rocks, 

i. e., rocks which, like sandstone, are formed of material deposited at a 

level lower than its source. In this country^the dunite associated with 

the corundum deposits of North Carolina has been regarded by Dr. A. A. 

Julien,2 who studied the rocks both in the field and under the microscope, 

as a deposit of olivine sand derived from an earlier eruptive mass. I>r. 

M. E. Wadsworth,3 after a critical examination, considered them to be 

eruptive, and my investigations of the same rocks convince me that 

Dr. Wadsworth's conclusion is correct. The dunite of North Carolina 

and the one in Elliott County, Kentucky, are essentially the same in 

structure and composition, and I believe are also of the same eruptive 

origin. Certain it is that the one in Kentucky is eruptive, and all the 

essential phenomena in North Carolina point in the same direction. It 

is important to note, however, a marked difference in the character of 

the alteration in the two cases. In the dunite of North Carolina, as 

well as in a number of undescribed peridotites of Northern California 

and elsewhere,4 which like it are found associated with highly contorted 

and metamorphosed strata, the olivine frequently alt ers to hornblende. 

In Kentucky, however, where regional metamorphis m is entirely absent, 

no such alteration has been observed.

CHEMICAL COMPOSITION.

The following table presents in a concise form all of the chemical 

analyses which have been made of the peridotite, its constituents, and 

associated rocks:

Chemical analyses of peridotite and associated rocks.

Water at 110° (H20)......

Phosphoric acid (PtOs) . . .

Ffirrona osldp. l"Fp.O)......

Olivine.

c.

0.14

0.66

40.05

0.07

0.04 

0.24

0.39

O Qfi

7.14

o

p7

<M

0.17

41.32

0.16

None 

0 91

21.21

4.21

7.93

Ilmenite

§

0.20

0.70

49.32

Trace 

0.74

2.84

27.81

6

Peridoti

,S

8.92

6.60

29.81

2.20

0.35

2.01

5.16

4.35

<9

Peridoti

S.

10.90

5.65

29.43

1.48

Trace 

0.14

2.36

9.06

'3

CO

0.51

60.56

1.19

0.30

16.19

5.19

2.41

s.2

00 O

03 O

3 P.

Caleareo one near

£«

0.85

2

OO

6.29

60.78

0.03

0.09

10.54

3.27

o

'33 o

f (-1 

0.' «

q-q>

O-S 

q 05 a-nJ

Pw a

g«

1.94

5 17

60.25

0.23

0.10

20.18

1.53

3.42

a> 0 

 o

A

Indurate dil

C5

8.78

41.32

0.48

0.08

20.71

2.59

5.46

0"35 

"1

0 &,

Fragme )eluded in

c-.S

1.40

9.00

O OQ

0.08

18.23

2.46

4.81

1 E. Kalkowsky: Elemente cler Lithologie, p. 236.

2 Proceedings Boston Society Natural History, Vol. XXII, p. 141.

3 Science, Vol. Ill, p. 286, April 18, 1884.

4 Mikroskopische Physiographic der petrographisch. wichtigen Mineralien. 

ganzlich urngearbeitete Auflage, pp. 412,413.

(378)

Zweite
DILLEB.J CHEMICAL COMPOSITION. 25

Chemical analyses of peridotite and associated rocks Continued.

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

Potasli (KzO). ............

Sulphur (S)...... .........'.

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

6

.3

o

c.

0.20

(CoO)

Trace

1.16

46.68

0.21

0.08

99.42

2

2

PH

£

fi Ql.

I.....

4.94

19.32

0.07

100. 58

 §

to

M

m.

0.20

0.23

8.68

0 10

100. 10

o

o

3

o

p^

3

0.23

0.05

7.69

32. 41

0.20

0.11

0.28

100. 86

2.781

J

"o

°C

(B

PH

2.

0.60

6.94

31. 6G

0.65

0.78

*0.20

0.30

100. 15

2.697

S

§

o

to

0.36

2.09

1.30

4.82

4.78

99 70

2 633

. ff .*tn

^ O

a -a

09 O

3 ft

[_, CQ

u a

£ ffl

0.10

10.15

1.59

2.36

1.41

QQ 78

<D

aa M

^fl rP

r^ ^

S cS

'3 B

&SJ

.5-j

g«

0.10

0.51

3

KO

3 17

0.39

100. 51

g

B

cS

T3 ®

M

S

0.17

9.91

1.91

0.88

7, 1Q

100. 03

0 .

A J

m o

<M ^

o C

42 V

s Cu

a -3 g's

S fl

OA I

21.17

9 (11

f. 08

2 53

100. 26

* In sulphides.

Analysis No. 5 of the peridotite was made by A. M. Peter and J. H. 

Kastlein the chemical laboratory of the Geological Survey of Kentucky. 

All the other analyses were made by T. M. Chatard in the chemical 

laboratory of the United States Geological Survey.

Although the freshest samples of the peridotite were selected for 

analysis, the large percentage of water and carbonic acid present indicates a high degree of alteration. As compared with the analyses of 

other typical peridotites the amount of silica appears very low, but this 

does not necessarily indicate that any of the silica has been removed, 

for its apparent decrease is due, at least in large part, to the addition 

of water and carbonic acid from external sources.

LOOSE FRAGMENTS OF FELDSPATHIC ROCKS FOUND WITH THE

PERIDOTITE.

At the localities marked 4 and 5 upon the map loose fragments of 

highly feldspathic rocks occur upon the surface, mixed with the soil containing garnets and ilmenite. The fragments found at the two places, 

although somewhat dissimilar, are holocrystalline and granitic in 

structure, altogether unlike the adjacent sandstones and shales, and it 

is evident that they belong to the eruptive mass. They deserve special 

attention and will be noticed separately, beginning with those found 

upon the hillside at locality 4, a short distance northwest of the site of 

the old furnace. Several fragments were found at this place, scattered 

along the border of the dike for a distance of 50 yards. The hand 

specimen looks very like a rotten syenite and is easily crumbled be-

(379)
26 ELLIOTT COUNTY PERIDOTITE. - [BULL. 38.

tween the fingers. Notwithstanding the fact of its feeble cohesion the 

feldspar, which is by far the most prominent mineral of the rock, exhibits numerous bright cleavage and crystal faces. Dark colored minerals are not conspicuous. Among these, ilmenite may be easily recognized by its jet black color and brilliant luster. Under the microscope 

the rock is seen to be composed chiefly of feldspar. Considerable 

quartz and ilmenite are present, with a trace of hornblende, sphene, and 

apatite. The feldspar is of two sorts, orthoclaseand plagioclase, readily 

distinguished by their optical characters. They are generally grown 

together as perthite and may be completely irregular in their interlock - 

ings, but frequently the parallel sheets of each, varying from .005 to 

.01 millimeter in thickness, join in the plane of the orthopinacoid and 

a*e quite regular in outline. The orthoclase is somewhat clouded by 

kaolinization, but the plagioclase is colorless and transparent, with 

bright polarization between crossed nicols. The polysynthetic twinning 

which characterizes the plagioclase is generally parallel to the clinopinacoid, but frequently associated with these lamellae are others parallel to the orthopinacoid. Cleavage lamellae of the plagioclase parallel to the base have a very small angle (2 degrees) of extinction. 

This fact indicates that the plagioclase is not pure albite, but has a 

considerable admixture of the anorthite molecule and is probably oligoclase. This conclusion is substantiated by a test with hydrofluorsilicic 

acid, which shows the presence of both calcium and sodium. The feldspar, especially the perthitic form, contains numerous inclusions. Besides apatite and ilmenite, the earlier products of crystallization, the 

feldspar contains numerous acicular groups of light brown scales, whose 

character could not be definitely determined. The scales are frequently 

hexagonal in form, and although all are in a row their hexagonal planes 

may make any angle with the longer axis of the group. These acicular 

groups generally lie at an angle of about 45 or 90 degrees to the plane 

of the perthitic lamellae.

Quartz occurs in clear, colorless grains, the nniaxial positive character of which can be easily demonstrated. It contains occasional liquid 

and gas inclusions, but none of the kind so common in the feldspar. 

Quartz and feldspar are each included in the other and must have 

crystallized synchronously. The green dichroic mineral regarded as 

hornblende does not appear with well defined crystallographic features. It has rather strong double refraction, but the angle of extinction could not be sharply determined in the absence of well defined 

cleavage. Chemical analysis No. 6 in the table is of this feldspathic 

rock. Its mineralogical and chemical constitution indicates that it belongs rather to the granites than to the syenites, although it is closely 

related to the latter group.

The other specimen of feldspathic rock collected near the eastern end 

of the dike at locality 5 is quite unlike the one j ust described. The only 

fragment found in this case is very solid and fresh in appearance and

(380)
INCLUSIONS IN PERIDOTITE. ^ ;/ ^k 27«

somewhat gneissoid in structure. In the hand specihi'e'uft appears t&lbe^ 

composed chiefly of feldspar and garnet and a smaller prop^iion of a 

greenish mineral, but in addition to these the microscope reveals the 

presence of small quantities of quartz, enstatite, apatite, and other accessory minerals. In structure it is holocrystalline and distinctly granular. None of its constituents, excepting the minute acicular inclusions, 

has a well defined crystallographic outline. The feldspar is plagioclase 

with a much larger angle of extinction and broader twinning lamellae 

than the oligoclase of the other fragment. Orthoclase, if present at all, 

is rare and does not appear in.perthitic grow th with plagioclase. Occasionally the feldspar is bent or broken, as if subjected to great strain 

sinceits crystallization. Nearly or quite a third of the rock is formed of 

garnet, which to the unaided eye looks very like the pyrope of the periclotite. It differs from the latter, however, very prominently under the 

microscope in containing numerous included microlites. These minute 

acicular crystals are of a yellowish mineral like rutile, but between 

crossed nicols are seen to be brilliantly doubly refracting with inclined 

extinction. The angle of extinction varies from 0 degree to 30 degrees, 

indicating that the mineral crystallizes in the monoclinic system. Cross 

sections of the small cry stals have a rhombic or elliptical outline. Earely 

these inclusions are arranged irregularly, but generally they appear to be 

nearly equally distributed in three sets. The longer axes of the crystals in each set are parallel, but the longer axes of the different sets 

make an angle of about 45 degrees with one another. Frequently these 

minute crystals are associated with cavities, as represented in the annexed figure 8.

The first example looks as though the crystal .had been formed by 

partly filling a cavity, of which a represents the portion remaining unoccupied. In the second example, however, the cavity e is 

between 1) and c, which are optically parallel, indicating 

that they are parts of the same crystal and that the cavity 

has been formed by dissolving away its middle portion. 

Although these inclusions are numerous in the garnet 

they are even more abundant in the green mineral, which 

has not been definitely determined. It has almost as 

high an index of refraction as garnet and is strongly 

doubly refracting. It is plainly biaxial, with extinction FJG "8 i"nciadea 

inclined to the indistinct cleavage. The quartz, ensta- microlites and cav 

tite, apatite, and a yellowish brown mineral like rutile ities in garnet> 

present nothing worthy of special mention. The structure and mmeralogical composition of this rock fragment closely ally it to the granulites.

The presence of the two kinds of fragments of feldspathic rocks intermingled with the soil resulting from the disintegration of the peridotite 

may be explained in many ways, but from the fact that the dike occurs 

in nearly horizontal, unaltered, stratified rocks, many scores of miles

(381)
28 ELLIOTT COUNTY PEEIDOTITE. [BULL. 38.

aw'ay from the nearest known outcrops of similar massive terranes, it is 

highly probable that the fragments are indigenous to the region and 

were brought to the surface by an eruption. Their striking dissimilarity in composition to the peridotite indicates that they cannot with any 

considerable degree of probability be regarded as early products of crystallization in the peridotitic magma, but must be looked upon rather as 

inclusions of the country rock brought up from beneath a vast thickness of unaltered Paleozoic strata. The presence of a number of granitic 

fragments, nearly in line along the border of the olivine rock, suggests 

that the granite may have reached the surface by an independent eruption instead of as an inclusion brought up from the depths by the peridotite.

AGE OF THE PEEIDOTITE.

Professor Crandall has kindly furnished rue the following field notes 

upon the general geological features of Eastern Kentucky, which have

fi

an important bearing upon the age of the peridotite:

The dike is found near the line which marks the eastern limit of the Silurian anticlinal of Ohio and Kentucky, as modified by the final uplift of the Carboniferous 

series. That the Silurian axis was involved somewhat in this movement is indicated 

by the conditions as now observed; but there remains a clearly defined anticlinal 

ridge, with the border of the Coal Measures on its eastward slope, as has been pointed 

out in various reports on the geology of Eastern Kentucky. The eastward dip is interrupted along a line which is, in a general way, parallel to the border of the coal 

field. This interruption is more or less prominent as marked by a reduced dip, or by 

horizontal beds, or even by a reverse dip of the exposed strata. The last condition 

is more noticeable in Elliott County than elsewhere. The line of change falls but a 

few miles east of the dike. The reverse and the varying dips eastward and southeast from this line are the result of the upheaval of the Cumberland coal field, a 

movement which hinged on the Silurian axis along this line. The Silurian axis still 

remains, a prominent, unmistakable feature, as remarked, but reduced in width eastward and somewhat obscured in the topography as modified by the resulting drainage, That there may have been profound fractures of the rock formations along this 

line of hinge movement" follows as a matter of course. The Elliott County dike may 

be supposed to add something to the probability of such, fractures as the result of this 

movement. The movement as described may, in turn, throw some light on the occurrence of this outlying dike.

Transverse to the axis of uplift are some minor wave-like undulations, especially 

southward, and involving Elliott County in part, as noticed in Lesley's report on the 

outcrop line of the eastern coal field of Kentucky. These undulations have a determinative relation to the drainage, as in the case of the Licking, the Red, and the 

Kentucky Rivers, and it is not improbable that they may have an important relation to the faults which traverse adjacent parts of the Silurian axis and terminate 

in the border of the coal field. The most striking modification of the general dip by 

transverse flexure is found along a belt which extends from the Big Sandy River, 

south of Louisa, in Lawrence County, to a point opposite to and but a few miles east 

of the dike. The dip along this belt is to the northward from a ridge of conglomerate rock, which elsewhere falls below the drainage along the border of the coal fields. 

It is along this slope that the oil and gas developments of Lawrence and Martin 

Counties are being made. The prominent geological basin centering at Willard is 

formed by a junction of this northward dip with the general southeast dip, increased 

by local depression. Willard is about 6 miles in a direct line northeast of the dike.

(382)
DILLER.I SUMMARY. 29

The dike is found near the juncture of two lines of flexure : one parallel with the 

axis of uplift of tide Coal Measures and the other a transverse or secondary undulation 

of considerable local prominence. Whether or not these conditions throw light on 

the occurrence of igneous rock far from any region of great disturbance, they form an 

interesting, if nob a necessary, background to any general view of the dike and its 

surroundings.

That the eruption of the peridotite occurred since the deposition of 

the Carboniferous strata with which it is associated is a matter that does 

not admit of question, but whether or not its extrusion took place at 

the close of the Carboniferous period synchronously with the plication 

of the Paleozoic strata of the Appalachian system is difficult to determine.

The very slight disturbance suffered by the strata through which the 

peridotite reached the surface suggests that its extrusion may not have 

been connected with the great orographic movements at the close of the 

Carboniferous age, but rather with the subsequent dislocations, like that 

of Pine Mountain in Southeastern Kentucky, which, according to Professor Shaler, occurred at a much later date.

SUMMABY.

The rock recently discovered by the State Geological Survey in Elliott 

County, Kentucky, is a peridotite, which on account of the great predominance of oli vine in its composition is closely related to dunite, such 

as occurs in the corundum region of North Carolina.

Among the interesting features of the peridotite is the occurrence of 

some of the oli vine in well defined crystals. It contains a considerable 

proportion of pyrope and ilmenite; the former, as in many other peridotites, is surrounded by a fibrous border composed chiefly of biotite.

The peridotite is associated with nearly horizontal Carboniferous sandstones and shales, from which it differs widely in chemical and mineralogical constitution. It not only includes numerous fragments, but has 

greatly indurated the shale near the contact and has itself suffered endomorphic effects in the production of a sphserolitic structure corresponding to that of variolites. These facts clearly indicate that the 

peridotite is eruptive and render its occurrence of much importance, 

for it so rarely happens that peridotites are found under such circumstances that their eruptive character can be fully established.

WASHINGTON, D. C., April 26,1886.

(383)

INDEX.

Apatite....................................................................11,26,27

Becke.Fr................................................................. 15

Biotite .......................................................10,11,13,14,15,17,20

C'hatard, T. M ............................................................13,17,25

Cohen, E ................................................................. 19

Crandall, A. E., field notes by............................................. 9,28

Diamond................................................................... 23

Dolomite .................................................................11,13,19

Dunite ...................................................................11,12,24

Dutton, C. E.............................................................. 9

Educational Rock Series, locality of specimens collected for................ 10

Enstatite...........................................................11,13,14,17,27

Furnace, old site of......................................................... 18

Garnet. See Pyrope.

Granite................................................................24,25,26,28

Granulite................................................................. 27

Hoeing, J. B.............................................................. 9

Hornblende.................................................. ....14,16,17,23,24,26

Ilmenite......................................................10,11,13,17,18,24,26

Inclusions in peridotite...........................................10,21,22,23,24,25

Iron, native .............................................................. 18

Irving, E. D...................................... ........................ 19

Judd,J. W.................................................. ............. 13

Julien, A. A .............................................................. 12,24

Kalkowsky, E ............................................................ 24

Kastle, J. H., and Peter, A. M............................................. 9,25

KelypMte ................................................................. 15

Lasaulx,A. von........................................................... 15,17

Lewis, H.Carvill.........................................'........... ...... 23

Magnetite.......................................................11,13,14,17,18,21

Muscovite ................................................................ 20

Octahedrite.........................................................11,13,18,19,22

Oligoclase ................................................................ 26,27

Olivine..................................................10,11,12,13,14,17,19,23,24

Orthoclaae.................................. ..............................21,26,27

Peter, A. M., and Kastle, J. H............................................. 9,25

Picotite................................................................... 17

Proctor, J.E.............................................................. 9

Pyrope .................................................10,11,13,15,16,17,18,24,27

Quartz .............................................................17,20,21,26,27

Eutile.................................................................... 20,27

Eosenbusch, H............................................................17,19,21

Schrauf, A................................................................ 15

Serpentine....................................................10,11,12,13,19,20,22

Sphene ................................................................... 26

Spilosite..---........---....--...--..-...--............................--. 21

Variolite............'..................-..-................................ 23

Wadsworth, M. E.........................................................12,19,24

. (385) 31

The bulletins of the United States Geological Survey are numbered in a cdntinuotd 

series and -will be bound iu volumes of convenient size. 

This bulletin will be included in Volume VI.