Art. ix.] Herrick-Johnson, Geology of the Alhuqitevque Sheet 195 
southern New Mexico up to the mouth of the Pecos River and 
southern Arizona; also a little of western Texas. Charles A. 
White found the whole upper Cretaceous in this region from 
the Dakota to the Laramie, while nothing lower than the 
Comanchie has ever been found in the Lower Cretaceous. 
The most important exposure of the Comanchie formation has 
been found in Sierra San Carlos in the Mexican State of 
Chihuahua. Here Dr. Parry found an exposure of over 4000 
ft. containing Comanchie fossils throughout, and consisting of 
bluish-gray compact limestones, comparatively pure, but, in 
part, argillaceous. 
The Great Interior Area. The following table gives the 
Upper Missouri River Section of Meek and Hayden, also the 
modification of the same as adapted by C. A. White this region 
(See Rev. of the Cret. Form, of N. A.): 
Upper Mo. River Section. Modification of Same. 
Montana Formation. 
Colorado Formation. 
Dakota Formation. 
No. I. Dakota Group. 
The Laramie formation is not included under any of the 
above heads, but it is found in different localities throughout 
the whole of the Great Interior Region. It is probable that no 
true marine fauna occurs in this formation, but brackish water 
mollusks, such as Ostrea, Anomia, Corbula, Corbucula, and 
Neritina, and such fresh water forms as Unio, Anomia, etc., 
have been frequently found. 
There has been some question as to whether this formation 
should be placed in the Cretaceous or the Tertiary. It is now, 
however, usually considered as a transitional period, but re- 
ferred to the Cretaceous formations. (See White’s “ Review of 
the Cret. Formations of the N. Amer., p. 148.) 
South Interior Region. This region comprises the whole of 
Colorado and portions of Kansas, Nebraska, Wyoming, Utah, 
Arizona, New Mexico, and north-western Texas. The strata, 
except a small portion in southern Kansas, are entirely of the 
