GEOLOGY OF LITTLE ROCKY MOUNTAINS 407 
section have been examined by Professor C. D. Walcott, who 
has identified the following species: 
Ptychoparia Owenu Hall. 
Obolella nana Meek and Hayden. 
Both are Middle Cambrian forms. 
Stlurvo- Devonian rocks.—Above the Cambrian series there are 
dark-colored, slate-gray and black, fetid limestones possessing 
the general characteristics of the Silurian and Devonian series 
as developed in the Rocky Mountain region to the westward. 
These rocks, however, have not yet been found to contain fos- 
sils, and the assumption of their Silurian age is based upon 
their lithological character and their position between the Cam- 
brian rocks and those of Carboniferous age. The Devonian 
was not recognized, but in its occurrence westward in the Rocky 
Mountain province, it is recognizable with difficulty, and the 
lithological chara¢gter of the rocks found here indicates that 
careful search may reveal characteristic fossils of this age. 
Carboniferous.—The Carboniferous rocks are well developed and 
form a series of somewhat thinly bedded limestones at the base, 
several hundred feet in thickness, which are capped by massive, 
heavy bedded, structureless limestones which appear to be char- 
acteristic of the upper part of the Carboniferous throughout the 
northern Rocky Mountain region. These are the limestones 
whose upturned beds form the encircling girdle of the moun- 
tains, and in which the picturesque canyons of the streams are 
cut. Characteristic Carboniferous fossils were observed at a 
number of exposures. Professor E. S. Dana collected a few 
fossils from these beds in the canyon east of Rock Creek, 
identified by Professor Whitfield* as follows: 
Glauconome sp.? 
Productus sp. 
Chonetes sp., resembles C.; granulifera Owen, also C.;  sub- 
umbona M, and W. 
Chonetes sp. 
«Reconnaissance from Carroll, Mont., to Yellowstone National Park, by Cou. 
Wma. LubDLow, Washington, 1876, p. 129. 
