178 
GEOLOGIC ATLAS OF THE UNITED STATES. 
FOLIO 30, YELLOWSTONE NATIONAL 
PARK, WYOMING, 1896. 
THE Yellowstone Park folio, recently issued, 
consists of six pages of descriptive text, three 
pages of illustrations, four topographic sheets 
(scale 1:125,000), and four sheets delineating 
the areal geology of the region. 
The general descriptive text, giving a succinct 
narrative of the geological history and develop- 
ment of the Park country from the time of the 
earliest continental land surfaces up to and in- 
eluding the hydro-thermal phenomena as seen 
to-day, was written by Arnold Hague, geologist 
in charge. It is followed by an account of the 
sedimentary rocks from the earliest Cambrian 
deposits to the Tertiary conglomerates, by 
Walter Harvey Weed, and a detailed petro- 
graphical description of the igneous rocks, by 
Joseph Paxson Iddings. 
The area of country covered by the Yellow- 
stone National Park folio lies between parallels 
44° and 45°, and meridians 110° and 111°. 
It is situated in the extreme northwest corner 
of Wyoming. By far the greater part of the 
Park is included within the area of the four 
atlas sheets, but a narrow strip lies to the 
northward in Montana, and a still narrower 
strip extends westward into Idaho and Mon- 
tana. In the organic act establishing the Park, 
Congress declared that the reservation was ‘dedi- 
cated and set apart as a publie park and pleas- 
ure ground for the benefit and enjoyment of 
the people.’ Owing to the marvelous display 
of geysers and hot springs of the region, and 
such remarkable physical features as the Grand 
Cafion and Yellowstone Lake, this folio possesses 
more than ordinary interest to geologists. 
The central portion of the Yellowstone Park 
is a broad voleanic plateau with an average 
elevation of 8,000 feet, surrounded on nearly all 
sides by mountains rising from 2,000 to 4,000 
feet above its general level. The continental 
watershed crosses the Park, separating the 
waters of the Atlantic from those of the Pacific, 
the Missouri andthe Columbia, by the way of 
the Yellowstone and the Snake, finding their 
sources on this plateau. 
The oldest rocks of this region are granites, 
gneisses and schists regarded as of Archean 
SCIENCE. 
[N. S. Von. VI. No. 135. 
age. They occur in all the mountain uplifts 
that encircle the Park, but are unknown in the 
central portion. Around these ancient conti- 
nental land masses there was deposited a con- 
formable series of sandstones, limestones and 
shales, extending from the time of the middle 
Cambrian, the lowest beds exposed through the 
upper Cambrian, Silurian, Devonian, Carbonif- 
erous Juratrias and Cretaceous, including the 
Laramie sandstone. Nearly every one of these 
great divisions of Paleozoic and Mesozoic time 
is characterized by a typical fauna. With the 
close of the deposition of the Laramie sand- 
stone the conformable series of sediments came 
to an end. The entire region was elevated 
above the sea, the elevation being accompanied 
by plication and folding ofstrata. This primary 
orographic uplift which blocked out the main 
ranges of the northern Rocky Mountains has 
been designated the post-Laramie movement. 
Tertiary sedimentary rocks occupy only small 
areas in the Park, the greater part of the re- 
gion being covered by extensive flows of lava. 
A heavy mass of coarse conglomerate, desig- 
nated the Pinyon conglomerate, has been re- 
ferred to the Eocene, and Pliocene conglomerate 
and coarse sands are well exposed in the escarp- 
ments of the Grand Cafion. 
Volcanic energy, which has played a great 
part in the geological development of the coun- 
try, was connected with the post-Laramie 
movement and followed closely upon the eleva- 
tion of the mountains and the accompanying 
dislocation and compression of strata. The 
eruptive masses in forcing their way upward 
sought egress along lines of least resistance, or 
wherever strain had been greatest in the crum- 
pled sediments. Volcanic outbursts continued 
on a grand scale throughout Tertiary time. 
During the Eocene and Miocene periods 
enormous volumes of fragmental ejectamenta, 
largely composed of andesitic breccias, were 
thrown out. The Absoraka Range was almost 
wholly built up of voleanic material. Hvyidence 
of this long-continued action is shown in the 
well-preserved fossil floras of Eocene and both 
lower and upper Miocene age. The famous 
fossil forests of the Yellowstone are of 
Miocene age. After. a period of great ero- 
sion the depressed basin lying between 
