752 GEOLOGY 



exactly, to the upper Laramie or post-Laramie) , and now to the 

 Tertiary (Eocene). They have heretofore been regarded, most 

 commonly, as the transition beds between the Cretaceous and the 

 Tertiary. It has been proposed recently to group these formations 

 together under the name Shoshone, and to class them as Eocene. 1 

 These formations are, generally speaking, unconformable on the 

 Laramie and, in some places seem hardly separable from the 

 recognized Tertiary 2 (Fort Union). Their reference to the Eocene 

 seems to be justified both on stratigraphic and paleontologic 

 grounds, so far as present data are concerned. 



The Pacific Coast 3 



The Cretaceous system is represented on the Pacific coast by 

 the marine Chico series. At the time of its origin, this series prob- 

 ably extended along the coast from Lower California to the Yukon. 

 The Chico series rests on the Shastan unconformably in some places, 4 

 and overlaps it at others. 5 The fauna of the Chico series is littoral. 

 Its oldest portion is older than the fauna of the Colorado series, and 

 its youngest is older than the fauna of the youngest Cretaceous beds 

 in some other places. 6 



Close of the Period 



About the close of the Cretaceous period a series of disturbances 

 was inaugurated on a scale which had not been equalled since the 

 close of the Paleozoic era. These changes furnish the basis for the 

 classification which makes the close of this period the close of an era. 

 These disturbances continued into later times, but the close of the 

 Cretaceous may be said to have been the time when the din! 

 had advanced so far as to make themselves felt profoundly. They 

 consisted of deformative movements, a part of which were orogenic, 

 and of igneous eruptions on an almost unprecedented scale. 



1 Cross, see footnote, p. 750. 



2 Here belong the Arapahoe, Denver, Middle Park, and Animas hi 

 Colorado, the Carbon, Evanston, and Ceratops beds of Wyoming, and tin- 

 Hell Creek, and perhaps the Livingston beds (at least in part) of Montana, 



3 Papers of Diller, Stanton, and Turner, cited under the Lower Cretaceous 

 (Shasta)', p. 7:;:;. 



4 Fairbanks, Jour. Geol., Vol. Ill, p. 426. 



5 Fairbanks, Am. Jour, of Sci., Vol. XLV, 1893, p. 478. 

 Stanton, Jour. Geol., Vol. XVII. 



