428 DESCEIPTIVE GEOLOGY. 



be counted, beaches of the more constant shore-line, while several others, 

 not so well preserved, have left more or less indication of the receding waters 

 of the basin. Barometrical observations were made at our camp in the Ter- 

 race Mountains, and from there careful instrumental determinations of the 

 height of the upper beach-line. These observations were referred to our 

 station-barometer at Matlin, and these again corrected by the railroad- 

 levels as a base. This measurement agrees very closely with determina- 

 tions made at Black Eock Point, where the position of the terrace was 

 found, by a series of careful observations, to be 940 feet above the lake- 

 level. South of the railroad, for 5 or 6 miles, the depressions of the Ter- 

 race Mountains are in many places below the level of the old lake, the 

 greater part of the range, like the Promontory, having stood as an island 

 in the sea. In these low, narrow depressions, the action of the shallow 

 water upon the shore is very clearly shown, with the beach-lines extending 

 across the range from east to west. Considerable accumulations of Qua- 

 ternary material skirt the base of the range, concealing the liniestone slopes 

 in many places for several hundred feet. It consists of beds of loose gravel 

 and sand, anc(. fine conglomerates, containing fragments of calcareous tufa, 

 which also frequently serves as a cement. Or binding material, for the con- 

 glomerate. The two groups of hills which rise out of the desert to the 

 southwest of the Terrace Mountains, known as the Rocky and Desert Hills, 

 were not visited by our parties. They have, however, been referred pro- 

 visionally to the Lower Coal-Measure formation, on grounds of general 

 analogy with the structure of this region, which is supported by the meagre 

 facts with regard to the rocks which compose them, which it has been pos- 

 sible to obtain from those who have visited these almost inaccessible points. 

 Raft River Mountains. — In the southern end of the Raft River 

 Mountains, a very considerable body of granite forms the central mass of 

 the range. It measures 10 or 12 miles in a north and south direction, 

 and 6 to 8 miles in width at its broadest expanse, culminating in Cita- 

 del Peak, a fine summit which rises nearly 2,500 feet above the level of the 

 lake. On the south and west, it is covered by heavy beds of limestone, 

 folding completely around its flanks, which have been referred to the Lower 

 Coal-Measure formation; while on the east side it falls away gradually 

 with easy slopes toward the valley of Clear Creek, until concealed by the 



