ANALYSES OF ROCKS, LABORATORY OF THE UNITED STATES

GEOLOGICAL SURVEY, 1880-1899.

By F. W. CLARKE.

INTRODUCTION.

The present Geological Survey of the United States was organized in 1879. In 1880 a chemical laboratory was established at Denver, in connection with the Colorado work, in charge of Dr. W. F. Hillebrand, with whom were associated Mr. Antony Guyard and, later, Mr. L. G. Eakins. In 1882 Dr. W. H. Melville was placed in charge of a second laboratory at San Francisco, and in the autumn of 1883 the central laboratory was started in Washington, with myself as chief chemist. In November, 1885, Dr. Hillebrand was transferred to Washington; early in 1888 he was followed by Mr. Eakins, and the Denver laboratory was discontinued. In the spring of 1890 Dr. Melville also was transferred to Washington, and since then the chemical work of the Survey has been concentrated at headquarters.

Up to January 1, 1900, nearly 4,400 analyses have been made in the laboratory at Washington. These represent rocks, minerals, ores, waters, sediments, coals, metals, and so on through all the range of substances with which geology has to do. There were also some hundreds of analyses made in the laboratories at Denver and San Francisco. A fair amount of research work upon mineralogical and analytical problems has also been done. In all of this work the following chemists have been employed: Charles Catlett, T. M. Chatard, F. W. Clarke, L. G. Eakins, F. A. Gooch, Antony Guyard, W. F. Hillebrand, W. H. Melville, R. B. Riggs, E. A. Schneider, George Steiger, H. N. Stokes, William Valentine, and J. E. Whitfield. As many as eight of these have been at work simultaneously; at present only four are connected with the Survey. Other officers of the Survey have been occupied more or less with chemical questions; but the men named in this list were connected directly with the laboratory. Some work for the chemical division has also been done by chemists not regularly on the rolls of the Survey; but their analyses, with the exception of a single group to be noted later, do not fall within the scope of this paper.

Quite naturally, on account of the activity of the petrographers, the dominant feature of the laboratory work has been the analysis of rocks. These have been studied in great numbers and in the most thorough way. The results have appeared in widely scattered publications,

official reports, monographs, bulletins, American and foreign journals, and so on. The object of this bulletin is to bring together this valuable material, together with such bibliographic and petrographic data as seems to be necessary in order to identify the specimens and to facilitate chemical discussion. Analyses of minerals have been included only when related to petrographic studies, appearing then in connection with the rocks to which they belong. Meteorites, of which twenty-seven have been analyzed, are brought into the work on account of their petrographic relations; and the groups of clays and soils have been admitted because of the bearing of these substances upon the study of slates and shales. The actual number of analyses given in

It may be observed that the classification thus indicated has not been rigorously followed. In a few instances the study of a sedimentary rock has been so related to that of its igneous neighbors that the analyses are best tabulated together; but these exceptional cases are few, and all are properly noted. The heading "igneous and crystalline rocks" has been used in the broadest and most liberal way, and doubtless many of the analyses given under it might properly be otherwise classified. In such cases of uncertainty, convenience has furnished the rule to follow.

Within each division of the analyses the classification chosen has been geographic. The petrographic grouping of the rocks would doubtless be best were petrographers agreed upon it; but their differences are many, and the chemist will do well to avoid them. The geographic method, moreover, has some advantages of its own; it facilitates the study of areas, it simplifies the bibliographic references, and it brings together, in great measure, the work of each petrographer for whom analyses have been made. Thus, most of Diller's work has been in California, most of Cross's in Colorado, and most of Iddings's in the Yellowstone National Park, and in each case the analyses are massed, and their discussion is practically uniform in character. As regards nomenclature, each rock has received the designation given it by its describer, and no liberties have been taken. This plan may cause some lack of uniformity; but no other procedure seemed to be practicable.

It will be noticed by anyone who uses this bulletin that the analyses vary as regards completeness. Among the sedimentary rocks, espe

cially, partial analyses are common; but in the igneous group thoroughness is more general. In the early days of the chemical division many analyses were made along the older lines, just as they are still made in many laboratories to-day-that is, only the main constituents, those having direct petrographic significance, were determined. In such analyses the minor ingredients, like titanium, phosphorus, barium, strontium, chlorine, etc., were ignored; and, although the results are satisfactory in some respects, they leave much to be desired. Latterly, greater completeness has been sought for, the work done has been much fuller, and the data obtained can be discussed with much higher approaches to accuracy. The old form of "complete analysis" is to be discouraged; it leads too often to erroneous conclusions; and only the best modern methods of work and of statement should be tolerated. The fuller analyses, moreover, have brought some interesting points to light; titanium now appears to be one of the more abundant elements, and barium and strontium are found to be almost universally diffused in igneous rocks in quite perceptible quantities.

On general principles the analysis of a rock and its petrographic description should be two parts of the same investigation, matching each other completely. In practice, however, this rule does not always hold, and the departures from it are in two opposite directions. For example, an analysis of the older type says nothing of titanium and phosphorus, while the microscope reveals the presence of sphene and apatite. In this case the petrographer has been more thorough than the chemist. On the other hand, a full and perfect analysis may be given, accompanied by a petrographic description of the most general kind, in which only the main mineral constituents of the rock are noted. Here the analysis has been incompletely used, and the petrographic discussion is defective. It is hoped that the publication of this material may lead to a clearer recognition of the mutuality which should exist between the chemical and the microscopic researches, and so bring, in the future, both lines of investigation more into harmony. Hitherto the chemist and the petrographer have worked too much apart, and each has too often misunderstood the purpose of the other. If the study of the thin section could always precede the analysis, the petrographic problems could be stated more clearly, and the chemical evidence might be rendered much more pertinent and satisfactory.

In a paper published some years ago,' on the relative abundance of the chemical elements, I computed the average composition of the primitive crust of the earth from 880 analyses of eruptive and crystalline rocks. Of these analyses only 207 were from the laboratories of the survey, while 673 were collected from various other American and foreign sources. A large proportion of them were incomplete, regarded from a modern point of view, and yet the results obtained were fairly conclusive. The material now available for similar discussion is much

1 Bull. U. S. Geol. Survey No. 78, 1891, p. 34.

better than that which was formerly used, and an average based upon it may not be out of place here.

In the bulletin now presented there are 830 complete analyses of rocks which are suitable for my purpose. I have also taken from the partial analyses given in the laboratory records 180 additional determinations of silica, 90 of lime, and 130 of alkalies. In 490 of the analyses there is discrimination between the water lost below 110° and that which is essential to the composition of the rocks; and this amounts to 0.40 per cent. Omitting this water, the average found may fairly represent the composition of the older crust of the earth, as deduced from a mass of data which are reasonably uniform in character and entitled to a high degree of credence. The mean for the more important constituents is as follows, with the old average given in a parallel column for comparison: