634 EEPOET UNITED STATES GEOLOGICAL SUEVEY. 



nary. In tlie eastern and southeastern portion of tlie area the Wahsatch 

 lake was outlined. 



It should be stated here that the western shore line of the Post Cre- 

 taceous has not been recognized, and that it is x>robable that if the 

 perix)heral portions of the Laramie Group could be observed, as Dr. 

 White remarks, some unconformity would be seen between it and the 

 Fox Hills Groui). He says:* " There must necessarily be some uncon- 

 formity between these groups in the peripheral portions of the Laramie, 

 because, as will be shown farther on, the area upon which its waters 

 rested was cut oft' from the great open sea by the elevation of portions 

 of the bottom ui^on Avhich the Fox Hills deposits were made." 



The fossils from the Laramie Group in our district are equivalent to 

 those of the Bear Eiver estuar^^ beds. These, Dr. White is inclined to 

 think, are somewhat older than the fossils from the group at other locali- 

 ties, and he therefore thinks tlie Post-Cretaceous upward movement may 

 have begun before the complete deposition of the strata composing the 

 group.t 



We have seen that after the uplift a iDeriod of enormous subaerial 

 erosion occurred, which was precedent to the deposition of the Upper 

 Wahsatch. It would seem to have been too great to have all been 

 caused during the earlier Wahsatch, although doubtless part of it is to 

 be so referred. In places the whole of the Cretaceous, Jurassic, and 

 Triassic has been removed, exposing the Carboniferous, and even some- 

 times the Silurian, upon the eroded edges of which the Wahsatch con- 

 glomerates rest. It seems probable, therefore, that a portion of this 

 erosion took place during the later portions of the Laramie period. This, 

 taken in connection with the fossils, appears to indicate that the eleva- 

 tion took place before the end of the Laramie period, and that, there- 

 fore, we do not have the entire series in our district. 



CE^OZOIC EOCKS. 



The Cenozoic areas of our district are of particular interest, but the 

 time allotted to the preparation of this report has been too short to enter 

 into the discussion of the various points that naturally arise when con- 

 sidering them. In early Cenozoic time the entire western portion of our 

 district was a land area, while the eastern was occupied by a portion of 

 the great lake which iliached eastward and southward for many miles. 

 Still later, the conditions appear to have been reversed, and while the 

 eastern part was above the sea-level, in the west was a series of lakes, 

 which continued from Tertiary to Quaternary time, and of whose late 

 existence we have a trace in the present Great Salt Lake. 



The deposits are all lacustrine, generally sandstones, but with calca- 

 reous layers at various horizons. The latest deposits are soft and friable, 

 being generally marls and loosely aggregated sands. Over the surface 

 of the entire district, except in the mountains, there is a thin covering 

 of uustratified drift, which will not be further considered in this report. 



TEBTIAEY. 



In considering the early Tertiary rocks of the district, I shall use only 

 the names of the groups, without reference to the terms Eocene or Mio- 

 cene. The Salt Lake Group I shall consider as Pliocene. 



^Bnlletin of tlie U. S. Geol. and Geograph. Survey of the Territories, Vol. IV, No. 

 4, p. 866. 



tSee pp. 246, 247 of this volume. 



