Mesozoic and Cxnozoic Geology and PalcBontoloyy. 237 



the usual lake terraces, of which there are two well-defined lines at 

 least, and the river terraces, which are confined to the streams, and do 

 not seem to have any direct connection with the former. The lowest 

 plain valley opposite the canon, near the water's edge, is 4,344 feet 

 above sea level; 1st terrace, 4,683 feet; 2d terrace, 4,776 feet; and 3d 

 terrace, 4,858 feet. These terraces show the gradual decrease, step by 

 step, of the waters of the ancient lake, and the operations of the little 

 streams pouring into it from the mountains on either side. Tlie 

 amount of local drift that has been swept down thi'ough the gorges or 

 canons and lodged at the opening is very great. At the immediate 

 mouth of the canon, the bowlders are quite large, varying in diameter 

 from a few inches to several feet. Westward toward the shore of the 

 lake the bowlders diminish in size and quantity, and the finer sedi- 

 ments, as sands and marls, increase, showing a constant decrease in 

 the power of the currents of the water after leaving the mouth of the 

 canon. 



The local drift is conspicuous in Logan Canon. It is composed of 

 rounded bowlders, with clays and marls, reaching a thickness of 100 to 

 150 feet in regular and horizontal strata, attached to the sides of the 

 gorge, and showing that, however turbulent the waters, the materials 

 were deposited in a lake. At the entrance of the canon are some re- 

 markable terraces, composed of sands, clays, marls and rounded 

 bowlders. 



A large portion of Utah is made up of nearl}- parallel ranges of 

 mountains, trending nearly north and south, with intervening valleys 

 of greater or less width, which, after their elevation, formed shore lines 

 for detached lakes or ba3^s. It would appear that the last lake-period 

 of this portion of the west commenced in the Pliocene epoch, and con- 

 tinued on up to the present time; that the waters once filled all these 

 valleys, so that they rested high upon the sides of the mountains, de- 

 positing what ,Prof. Hayden called the Salt Lake Group, gradually 

 passing into the Post-pliocene deposits which verge upon our present 

 period. It is quite possible that there have been oscillations of level 

 in these modern lake-waters; but so far as the proofs go, this great in- 

 land lake may have continued quite uniform until the terrace epoch, 

 and that then the waters graduall}^ receded to their present position. 



The immediate valley of Bear river, near the crossing, is interesting 

 on account of the fine development of the lake-deposit, which is com- 

 posed of clay, sand, and marl, 3-ellow and rusty-drab color, and attains 

 a thickness of 200 to 300 feet. The elevation of Bear river valle}', at 



