0. a Marsh— Geology of the Uintah Mountains. 197 



wl.ich predominates in nearly all the strata of the Uintah Mont)- 

 tiiiiis. These beds are evidently of Mesozoic a<]fe. an<l iiidiiu' 

 2iV to 45° to the southward. At one or two points, lar.Lre masses 

 of white compact gypsum were noticed in the sandstones. Tlie 

 oldest rocks observed were hard gray and purple sandstones and 

 quartzites, extending to the bottom of the degpest canons, and 

 apparently forming the central mass of the Uintah range, in 

 place of the granitic nucleus, which gives to the eastern Hocky 

 Mountains and the Sierra Nevadas their most marked diaiacter. 



While descending the northern slope of the mountain^ t< >\vaid 

 the great Tertiary basin of the Green Eiver, which htv in the 

 distance, 2000 feet below us, we passed over a high li.lsiv. tioin 

 the summit of which appeared one of the most stnlxin.! and 

 instructive views of geological structure to be seen in any 

 country. Sweeping in gentle curves around the has'' '-t the 

 mountains, from near where we stood, many miles to tli. north- 

 ward, was a descending series of concentric, wave-like ri.lg's, 

 formed of the upturned edges of different colored strata, which 

 dipped successively away from the Uintahs ; those nearest to 

 us, 40° or more, those at a distance, seemingly but little,— alto- 

 gether a scene never to be forgotten. Apparently we had be- 

 fore us a geological series from the Palaeozoic to the Tertiary, 

 but to study it step by step, as we strongly wished, our limited 

 time forbade, and reluctantly we hurried on our journey. Our 

 Indian guide led us across a very deep mountain gorge, called 

 by the hunters of this region " Sheep Creek Canon," through 

 which a small stream flows eastward into the Green River. The 

 sides of this gorge, where we crossed it, about ten mdes above 

 its mouth, are composed of light colored shales, and yellowish, 

 friable sandstones, highly inclined, and towering into precipitous 

 chffs, some of them nearly 1000 feet in height 



In ascending the northern bank, through a narrow and almost 

 impassable side ravine, we passed over a bed of light gray 

 limestone, about thirty feet in thickness, which rested conform- 

 ably on the sandstones below, and was inclined to the N.VV. at 

 an angle of 25°. This limestone contained an abundance ol 

 ^V-il-^ of characteristic types, that at once established its Juras- 

 ^"f :ige. Among the most interesting of these were two species 

 01 Trigonia, one of Camptmectes, a Volselh, a small Osirea, a 

 ^eritella, resembling K Nebrascensis M. and H., an Act^-onina 

 and a amntfem,— nearly all undescribed,— with specimens ol 

 Pentacnnus asteriscus M. and H. The right humerus of a small 

 Crocodilian was found in the same stratum. Resting immedi- 

 ately on this fossiliferous limestone, was a series of red and gray 

 shales, with intercalated sandstone layers, perhaps m all lou 

 feet in thickness. In the red beds, white gypsum was abundant, 

 ^ the form of fibrous seams, and especiaUy m mterstratitiea 



