REVIEWS 711 
and the lime is derived from the Madison limestone. The Laramie 
strata are exposed near the base of Pinyon Peak, as shown by the char- 
acteristic Wolverine flora. The conglomerate of Pinyon Peak is prok- 
ably Eocene, as it underlies the basic breccias of the Absaroka range and 
overlies unconformably the Laramie sandstones. Outlet Canyon, the 
picturesque gorge cut through Chicken Ridge, at one time served as an 
outlet into Snake River for the waters of Yellowstone Lake. The Yel- 
lowstone Canyon now furnishes an outlet for these waters into the 
Atlantic, instead of into the Pacific. Two Ocean Plateau, which rises 
10,000 feet above the sea level, forms a part of the Absaroka Range. 
It is made up of volcanic breccias and tuffs. 
Chapter six describes the southern end of the Snowy range, which 
forms the northeast corner of the park. It consists of a broad core of 
crystalline rocks, bordered by Paleozoic rocks, which dip away from the 
crystalline axis. Detailed sections of the Paleozoic sedimentary rocks 
are given, but the igneous rocks are described in other chapters. 
Chapter seven is especially interesting to petrologists, as it describes 
in detail the structural features and petrographic characteristics of a 
dissected volcano in the Crandall Creek basin. It lies on the border of 
the park forest reservation and east of the park proper. ‘The great 
value to petrology lies in the clear delineation of the inside of a volcano, 
and in giving additional field evidence of the gradation of coarsely 
crystalline so-called Plutonic rocks into the glassy eruptives. ‘The 
coarsely crystalline gabbros and diorites, with smaller bodies of granite, 
exposed for a height of 3000 feet, are plainly seen to have been intruded 
intoavast accumulation of basaltic tuffand scoriaceous breccia. From this 
coarsely crystalline mass as a center, dikes of fine-grained rock pene- 
trate the surrounding lavas in all directions, the dike rocks becoming 
fine-grained rapidly as they leave the once heated core. They form a 
network of branches which connect the outlying aphanitic and character- 
istically volcanic rocks with the more crystalline dikes near the core 
which finally merge into the granular body of the gabbro and dorite.” 
The whole forms one complex network so closely interwoven that the 
gabbros of the core are as truly volcanic as the glasses on the surface. 
The volcano has built itself upon a ridge of eroded Paleozoic rocks, 
and beneath the volcano are remnants of Eocene breccias and lava 
flows. 
The next chapter treats of the Absaroka range which consists mainly 
of volcanic breccias with smaller quantities of massive flows. It contains 
