12 ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. [no. 228. 
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 valu- 
able material, together with such bibliographic and petrographic data 
as seems to be necessary in order to identify the specimens and to facili- 
tate chemical discussion. Analyses of minerals have been included 
only when related to petrographic studies, appearing then in connec- 
tion with the rocks to which they belong. Meteorites, of which 
twenty-nine 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 
the bulletin is as follows: 
Igneous and crystalline rocks 1, 047 
Mineral separations 100 
Meteorites, and separations from them 62 
Sandstones, cherts, and sinters 60 
Carbonate rocks 234 
Slates and shales 60 
Clays, soils, etc 109 
Total 1, 672 
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 dif- 
ferences 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 petrog- 
rapher 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 
