236 GEOLOG"X OF THE DEXYElt BASIN. 



conglomerate reveals the extentof the stratigraphic break really existing 

 between the formations. The pre-Arapahoe uplift semis to have been 

 greatest in the mountain areas of Colorado and Montana, bul a study of 

 the various known facts leads the writer to the view, presented in more 

 detail below, thai large areas adjacent to the mountains wen- raised some- 

 what above sea-level at the time of the more pronounced mountain uplift, 

 and thai in the interval before subsidence caused the lakes of the Arapahoe 

 to be formed the land surface of the Laramie sediments on the plains may 

 have been verj little modified while great erosion took place in the moun- 

 tains. Or the loose and unconsolidated Laramie sediments of the plains, 

 being not much elevated above baselevel, may have wasted so evenly that 

 subsequent deposits upon them now seem conformable. 



The beds of Converse County, of the Judith Liver Basin in Montana, 

 and the area between them, the Animas River beds below Durango, and 

 the post-Laramie formations of other districts, occupy positions removed 

 from the regions of greatest disturbance, and it is natural that they should 

 seem conformable with the underlying strata, whatever they may he. In 

 the Livingston region the post-Laramie formation of that name lies with 

 apparent conformity on the Laramie, as seen in the Bozeman and other 

 sections, bul to tin' w estw ard its base transgresses the edges of the Laramie, 

 and iu the Three Forks area a great angular unconformity is seen ;it die 

 base of the Livingston. 



Their are many places in the West where the section of visible sedi- 

 mentary formations from the Cambrian to the Cretaceous seems a conform- 

 able one. and it has frequently been spoken of as such. But the researches 

 of the last two decades have pro\cn the existence of many important strati- 

 graphic breaks in this series, which are in certain places shown as great 

 unconformities hut can not he identified at other points. Especially in the 

 plains country adjacent to the Rocky Mountains conformity of formations 

 can not be assumed to prove continuity of sedimentation. The visihle 

 conformity between the Ceratops beds and the Fox Hills in Converse 



County can not hi' accepted, contrary to other evidence, as proving the 



former to have been deposited in the epoch next succeeding the Fox Hills. 



