732 GEOLOGY 



some terrestrial in origin. The marine part of the system includes 

 much limestone. 



From Texas, the Comanchean formal ions, or some of them, 

 originally spread northward into Kansas, 1 northwestward to Col- 

 orado, and westward to Arizona. Though they appear at the 

 surface in small areas only, their extent may be considerable 

 beneath younger formations. 



In Mexico. The Comanchean of Mexico is mainly limestone, 

 and, though but imperfectly known, has been estimated to have 

 the extraordinary thickness of 10,000 to 20,000 feet. Its distribu- 

 tion is such as to show that a large part of that country was beneath 

 the sea. It has been conjectured that the waters of the Atlantic 

 and Pacific mingled over the site of some part of Mexico at this t ime, 

 but this is uncertain. If the oceans were connected, it was probal >ly 

 across southern Mexico, or perhaps Central America. At any rate, 

 there does not seem to have been free faunal intermigration between 

 the Gulf coast and the coast of California. In its abundance of 

 limestone, the series of Texas and Mexico resemble the Lower 

 Cretaceous of the northern part of South America, and southern 



Europe. 



The Northern Interior 



Though the sea is not known to have had access to the western 

 interior of North America north of Kansas during the Comanchean 

 period, clastic beds of terrestrial origin, which are perhaps Coman- 

 chean, are known at various points farther north. The beds in 

 question, the Morrison, 2 Como, and Atlantosaurus beds, are 1 

 known along the Front Range through Colorado and Wyomini:, 

 and in the Black Hills, 3 though they probably reach northward to 

 Montana. If all the beds thought to be the equivalent of the Mor- 

 rison, are really so, the formation is widely distributed. These beds 

 are often regarded as late Jurassic, 4 and this may be their proper 

 classification. 



In Montana, Alberta, and Assiniboia, there are beds (the Konte- 



1 Prosser, "Comanchean Series of Kansas," tin- t'niv. (icol. Surv. of K:m<., 

 Vol. II, 1897. 



2 Cross, Pike's Peak folio, U. S. Geol. Surv., Is'.i \. 



3 Ward, Jour. Geol., Vol. II, p. 250. 



4 Knight, Bull. !.">, \Vyo. Kxp. Station, p. l:;i. 



