PKAtE.] KESUME MESOZOIC AND POST-CEETACEOUS. 633 



represented the western edge of the lake, but it soon spread so that it 

 reached from the Wind River Mountains to the very base of the Wyoming 

 Eange and around its southern end, westward to the Bear River Range. 



At first I was somewhat inclined to consider the faulting along the 

 Wyoming and Salt River Ranges as of later date than the Post-Creta- 

 ceous fold which is seen in the ranges and the eastern outlying ridge, but 

 resting on the eroded edges of the Laramie sandstones which enter into 

 this fold I found Wahsatch conglomerates composed of limestone peb- 

 bles, that, without doubt, came from the main range, which must, there- 

 fore, have formed a portion of the shore-line of the lake in which the 

 conglomerates were deposited, and from the erosion of this land area 

 they were formed. I therefore consider the folding and faulting to have 

 occurred at approximately the same time. 



In the western portions of the district the Cretaceous and overlying 

 rocks are absent, probably from erosion, so that we cannot now tell the 

 westward extent of the formation. The Jurassic is seen on the eastern 

 side of the folds which form the northern extensions of the Wahsatch 

 Range. 



The region westward from what is now the Green River Basin was 

 lifted above the level of the sea and probably added to the land area, 

 defined at the end of the Carboniferous, which was farther west. 



I have spoken of the isolated ranges in the Blackfoot region and in 

 the Cache Valley region. They now exist as monoclinal ranges, but evi- 

 dence is not difficult to obtain that they are simply the eroded fragments 

 of anticlinals. I am inclined to regard their age the same as that of the 

 Wyoming and Salt River Ranges, although they appear to be much more 

 eroded, as if they had been subjected to the erosive influences for a much 

 longer period of time. We have seen, however, that, as far as seen, the 

 Cretaceous formation is perfectly conformable with the Jurassic ; so that 

 there is no evidence of an upheaval within the limits of our district at 

 the end of the Jurassic. The sediments indicate a progressive subsi- 

 dence from the Jurassic through the Cretaceous. 



To recapitulate briefly, the facts observed in the district seem to indi- 

 cate — 



1. A shallowing of the sea at the beginning of the Trias due to the 

 rising of a land area somewhere to the westward. 



2. A general subsidence throughout the Trias, with oscillations of 

 level. 



3. The ushering in of the Jurassic by a somewhat paroxysmal subsi- 

 dence which considerably deepened the sea. This was probably due to 

 a Jurassic uplift in some other portion of the continent. 



4. Subsidence during the latter part of the period preceded by a period 

 of comparative rest. The sea-bottom appears to have been raised by a 

 succession of deposits of fragmental rocks, which then subsided gradu- 

 ally and successively through the latter part of the Jurassic and through 

 the Cretaceous. 



5. The continuance of the subsidence through the Post-Cretaceous and 

 the shallowing of the sea towards its close probably by a general eleva- 

 tion towards the close of the period which perhaps foreshadowed the 

 disturbance which was to take place after the deposition of its sediments 

 was completed. 



6. Intense disturbance at the end of the Post-Cretaceous (as exposed 

 in our district) which resulted in the upheaval of the area west from what 

 is now the Green River Basin to beyond the western line of our district. 

 The rocks of the whole region were folded and faulted in an extraordi- 



