192 0. a Marsh— Geology of the Uintah Mountains. 



our geological observations were necessarily confined mainly to 

 the immediate route pursued, and even then, in the limited time 

 at our command, could not be systematically conducted. Tk 

 region passed over, however, proved to be one of the most 

 interesting fields for geological research yet discovered in this 

 country, and hence the results obtained, although fi-agmentaiy, 

 will add something to the previous knowledge of Eocky Mom- 



Fort Bridger, in Wyoming, from which the Yale party started 

 on their expedition in September last, is situated at the northern 

 base of the Uintah Mountains, about 7000 feet above the sea 

 The surrounding plain is part of a great basin of denudation, 

 washed out of light-colored clays and soft sandstones of Tertiary 

 age, the deposits in one of the great fresh-water lakes, that re- 

 placed the Cretaceous sea from which the mass of the Kocky 

 Mountains emerged. Eemnants of the strata removed may ^ 

 seen at various points around ; some in the shape of flat, isolated 

 buttes, and others forming benches, resting horizontally against 

 the sides of the mountains. These fragments serve to show the 

 great original thickness of this lake deposit, which cannot, ap- 

 parently, have been less than 1500 feet, and may have been mncH 

 greater. A few miles to the southeast, these soft strata have 

 still further escaped denudation, and are weathered out into 

 fantastic, conical forms, resembling those of the "Mauvaisfe 

 Terres " formation of Nebraska and Dakota. These blufls^are 

 known in this region as the " Grizzly Buttes," and through them 

 lay our route to the Green Eiver. • 



A careful examination of this " Bad Land " district soon m 

 dicated that a fossil, vertebrate fauna of peculiar interest v^ 

 here entombed; one apparently older and quite distin^'* T 

 that preserved in the great Miocene lake-basin east oithem^ 

 Mountains, which we had recently explored. In the latter ur 

 posit, the remains of ruminating mammals were especiaiij , 

 merous, while the entire absence of fishes, and of rep{f^^''Lea 

 the exception of a single species of tortoise, was a well mar 

 feature. Here, however, reptilian life had evidently been au 

 dant, and was represented by all its principal forms. ^J^ ^^ 

 lans, tortoises, lizards, serpents, and fishes had swarmed i".^ 

 waters of this tropical lake; while Tapiroid maramals, 

 many smaller quadrupeds, had lived near its borders. I^- 

 remains had long been weathering out of the " G^J^^^m^ 

 which offered so inviting a field, that we devoted a ioM^, ^ 

 their exploration, and were rewarded by the discovei^^ 

 large number of extinct vertebrates new to science, ^^i^^ 

 be described by the writer at an early day. , ^„, the 



-Proceeding eastward along Cottonwood Creek, and o> ^^ 

 dmde to Henry's Fork, we found the same Tertiary deposit 



