770 THE AMERICAN NATURALIST. [VoL. XXXIV. 
GEOLOGY. 
The Yellowstone National Park.!— The final results of detailed 
geological investigation in the Yellowstone Park by Arnold Hague, 
geologist in charge of the survey, are to be published in a monograph 
consisting of several volumes. Part II of the series has been issued, 
containing descriptive geology of portions of the area and special 
papers on petrography and paleontology; several of these, notably 
those chapters by Professor Iddings, have already been printed in 
abstract, or more fully in annual reports of the survey. The authors 
of the several chapters are: Arnold Hague on the Mesozoic ridges of 
the southern part of the park, J. P. Iddings and W. H. Weed on the 
Gallatin Mountains and the Tetons, Weed on the Snowy Range, 
Iddings on petrography, the rhyolites, and some description of por- 
tions of the Absaroka Range, C. D. Walcott and G. H. Girty on 
Paleozoic fossils, T. W. Stanton on Mesozoic fossils, and F. H. 
Knowlton on the fossil flora. 
South of the park the Teton Range contains a nucleus of crystal- 
line schists and gneisses overlain by flexed Paleozoic and Meso- 
zoic strata; these were deeply eroded and covered by breccias and 
rhyolites, the latter forming vast flows, which constitute a large por- 
tion of the present Yellowstone plateau. In the Gallatin Mountains, 
northwest of the park, strata ranging from Cambrian to Cretaceous 
have been elevated, folded, and faulted, and at the close of the 
Laramie the rdcks were invaded by dikes, sheets, and laccoliths of 
igneous rock. In comparing the rocks of Electric Peak and Sepul- 
chre Mountain, the former coarsely crystalline and the latter volcanic, 
in close proximity, Iddings has determined that diorites may be 
chemically identical with andesites of different mineral composition. 
Like the Tetons, the Snowy Range, northeast of the park, has an 
archzan core bordered by sediments dipping toward the lavas. 
In the southern part of the park a number of ridges of Cretaceous 
sandstone occur, with the rhyolites abutting against their upturned 
anks. There are here several exposures of dacite or quartz 
andesite, apparently older than the rhyolite. A sandstone near the 
base of Pinyon Peak contains Laramie plants; a conglomerate 
1 Geology of the Yellowstone National Park, Monograph XXXII, U. S. Geolgt 
cal Survey, Pt. ii, Descriptive Geology, Petrography, and Paleontology, by Arnold 
Hague, J. P. Iddings, W. H. Weed, C. D. Walcott, G. H. Girty, T. W. Stanton» 
and F. H. Knowlton. xvii+791 pp., 121 plates. Washington, 1899. 
