46 GEOLOGICAL SURVEY OF THE TERRITORIES. 



cerned, I have observed no locality where there appeared to be any 

 striking noncouforuiity between the Fox Hills group and the Lignitic 

 group above. That there may have been intervals of time, during 

 which the (3retaceous sediments were not deposited ; that there may 

 have been dry land over large areas, is not impossible, but there could 

 have been no great degree of erosion of the surface of the upper Cre- 

 taceous beds. This apparent conformity, while in certain localities 

 the upper Cretaceous beds received a very much increased thickness, 

 may be due to a far more rapid deposition. In almost all cases, the 

 transition from the Fox Hills group to the brackish- water deposits of 

 the Lignitic seems to have been gradual, with no visible physical break 

 of importance. The great break seems to be illustrated only in the 

 entire change in the animal and vegetable life. 



But the time at my disposal will not permit me to discuss here many 

 important questions in this connection. For the details of the geology 

 of the Eastern base of the mountains in Colorado, the reader is referred 

 to the i)revious annual reports of the survey, especially the one for 1873. 



