560 Notices of Memoirs—Prof. Iddings— Volcano in Wyoming. 
under the charge of Mr. Arnold Hague, of the United States Geo- 
logical Survey. This paper is an extract from a chapter of the final 
report on the Yellowstone National Park, in process of completion, 
and the writer is indebted to Major J. W. Powell, Director of the 
Survey, and to Mr. Hague, chief of the division, for permission to 
present it at this time in anticipation of the publication of the final 
report. 
"The area of volcanic rocks described is but a small portion of the 
great belt of igneous material that forms the mountains of the 
Absaroka range, lying along the eastern margin of the Yellowstone 
Park. The volcano of Crandall Basin is one of a chain of volcanic 
centres situated along the northern and eastern borders of the 
Yellowstone Park, which are all distinguished by a greater or less 
development of radiating dykes, and by a crystalline core eroded to a 
variable extent. 
The Paleozoic and Mesozoic strata, which formed an almost 
continuous series to the coal-bearing Laramie, had been greatly 
disturbed, and almost completely eroded in places, before the 
volcanic ejectamenta in this vicinity were thrown upon them. The- 
period of their eruption is therefore post-Laramie, presumably early 
Tertiary. 
The first eruptions of andesite were followed by those of basalt in 
great quantities, and these by others of andesite and basalt, like the 
first. This was succeeded by a period of extensive erosion, reducing 
the country to nearly its present form. Then came the eruption of 
a vast flood of rhyolite, constituting the Park Plateau, which was 
followed, in this region, by smaller outbreaks of basalt. The last 
phase of volcanic activity is found in the geys rs and fumaroles 
which have rendered the region famous. 
The volcano of Crandall Basin consists chiefly of the first series 
of basic andesites and basalts. The earliest acid andesite which 
occurs beneath these rocks appears to be the remnant of oe 
from neighbouring centres. 
Nothing remains of the original outline of the volcano! The 
district is now covered by systems of valleys and ridges of mountain 
peaks that rise 2,000 to 5,000 feet above the valley bottoms. The 
geological structure of the country, however, makes its original 
character evident. 
The outlying portions of the district to the south, west, and north 
consist of nearly horizontally bedded tuffs and subaérial breccias of 
basic andesite and basalt. With these are intercalated some massive 
lava-flows, which are scarce in the lower parts of the breccia, but 
predominate in the highest parts above an altitude of 10,000 feet. 
Here they constitute the summits of the highest peaks. 
In contrast to the well-bedded breccias around the margin of the 
district the central portion consists of chaotic and orderless aceumula- 
tions of scoriaceous breccia with some massive flows. These breccias 
carry larger fragments of rock and exhibit greater uniformity in 
petrographical character. 
A still more noticeable feature of the central portion of the district 
