3Ieso.zow and Coinozoic Geology and Paloiontology. 199 



range of moimtains, but extending as far to the southwestward as the 

 southwest corner of Utah, and its eastern limit is far out on the great 

 plains, east of the Rocky Mountains, where it is covered from view by 

 later formations and the prevailing debris of the plains. These limits 

 indicate for the ancient Laramie sea a length of about 1,000 miles 

 north and south, and a maximum width of not less than 500 miles. 

 Its ]-eal dimensions were no doubt greater than those here indicated, 

 especially its length; and we may safely assume that this great 

 brackish-water sea had an area of not less than 500,000 square miles. 

 The present range of the Rocky Mountains, which has ueen entirely 

 raised as a mountain range since the close of the Laramie period, 

 traverses almost the entire length of this great area, and far the 

 greater part of the other extensive and numerous displacements which 

 the strata of the different geological ages have suffered within that 

 great area, have also taken place since all the Laramie strata were 

 deposited, although some of those changes thus especially referred to 

 began before the close of the Laramie period. 



The invertebrate fauna consists almost wholl}' of brackish-water, 

 fresh-water and land mollusca. Species belonging to all three of these 

 categories are often found commingled in the same strata, but it is 

 also often the case that certain strata, sometimes only thin la^^ers, 

 which contain the fresh-water and land molluscs alternate with those 

 which contain the brackish-water species. All the species of fresh- 

 water and land mollusca which prevailed during the Laramie period, 

 seem to have ceased with the disappearance of their contemporary 

 brackish-water forms, although the}^ were succeeded by other fresh- 

 water and land species. 



He described from Point of Rocks' station, Bitter Creek valle^^, 

 Wyoming, Axitima holmesana; from the mouth of Sulphur creek. 

 Bear river valley, Wyoming, Bhytophorus meeJci ; from the Cretaceous 

 of Collin count3% Texas, Ostrea blacki, JSxogyra ivincheUt, Pteria 

 (?) stahilitatis; from Bexar county, Texas, Exogyra forniculata; 

 from Bell count^^ Texas, Pachymya compacta, Thracia mymformis; 

 from the estuary strata of the age of the T^'ox Hills Group at Coalville, 

 Utah, Anomia propatoris ; from the Fox Hills Group at Cimarron, 

 New Mexico, Barhatia harhulata; from Dodson's Ranch, near Pueblo, 

 Colorado, Llspodesthes ohscurata; from the Dakota Group, Saline 

 county, Kansas, Pteria salinensis, GervilUa mudgeana\ from the Fort 

 Pierre Group at Fort Shaw near Muscleshell river, Montana, Tessarolax 

 hitzi; and from the Cretaceous of Yellow Stone river, Montana, Fas- . 

 ciolaria alleni. 



