CEETACEOUS PLAINS OF COLORADO. 63 



lies between the Cache la Poudre and Big Thompson, west of Greeley and 

 Evans ; the most westerly occurrence being some 8 miles west of the former 

 town in a bed which dips about 1° to the eastward. They also occur on 

 Lone Tree Creek. On Crow Creek, about 4 miles above the mouth, and 

 between the two streams, several miles north of the South Platte. 

 The following species have been identified : 



Avicula Nebrascana. 



Avicula cancellata. 



Cardium speciosum. 



Mactra Warrenana. 



Nucula planimarginata. 



In addition to the above, Prof J. J. Stevenson' has- since obtained from 



near Evans and Platteville, just southeast from the map, the following 

 species : 



Ammonites lobatus. -' 



Mactra alta. 



Anchura — f 



Still later, members of Dr. Hayden's^ corps have visited the region 

 and collected most of the above species. It is evident that this group of 

 fossils which occurs together in so many localities within such a limited 

 area, in beds of precisely the same physical habit and composition, and lying 

 approximately level, belong to the same geographical horizon. Indeed, the 

 beds may be traced without much difficulty along the Big Thompson and 

 Cache la Poudre Valleys, and then eastward up tlie valleys of the northern 

 tributaries to the South Platte. These sandstones form the exposed banks" 

 along Crow and Lone Tree Creeks, and may be traced northward, passing 

 under the Tertiary of Chalk Bluffs. 



No organic remains were obtained from the beds in close proximity to 

 carbonaceous clays and coal-layers east of the Denver Pacific Railroad, 

 but the structural relations of the beds is such that there can be no doubt 

 that the thin layers of coal occur under, or rather interstratified in, the red 

 sandstones, with well-defined Cretaceous marine invertebrata overlying 



'The Geological Relations of the Lignitic Groups, by J. J. Stevenson, 1875. 

 ^United States Geological and Geographical Survey of Colorado, Washington, 1876. 



