HYPOGEIC WORK. 361 



described by McConnell and Dawson. Farther south, in Utah, stands the 

 Wasatch Eange of the same Larainide system. The accompanying map of 

 the Wasatch is a reduction of the colored geological map in the Atlas of the 

 Eeport of the Fortieth Parallel Survey under Clarence King, and the 

 highly instructive facts here presented are from King's volume. 



The Wasatch Mountains extend for more than a hundred miles along the 

 east side of the Great Salt Lake Valley. They face west with a bold front, 

 rising abruptly from the plain to a height of 5000 to 6000 feet, which is 

 10,000 to 12,000 feet above tide level. At the western foot are Ogden, Uinta, 

 Salt Lake City, and Provo. The eastern slopes are more gradual. East of 

 its southern half stretch away the Uinta Mountains for 150 miles, a great 

 east-west plateau, or table-land, feebly anticlinal in structure, and 10,000 to 

 over 13,000 feet high. Only one fourth of its length is within the limits of 

 the map. North of the Uinta Mountains there is the great "Wasatch 

 Eocene basin," lettered W on the map, 5000 to 7000 feet above the sea level, 

 and south of it the "Uinta Eocene basin," nearly 10,000 feet high, let- 

 tered U. 



One remarkable feature of the Wasatch Eange is its backbone of Ar- 

 chaean rocks along its western front, — a mountain range of Archaean origin 

 which stood there, submerged or emerged, through all the rock-making and 

 mountain-making of Paleozoic and Mesozoic time, the prototype and model- 

 ler of the later Wasatch Mountains. There are four Archaean areas in sight 

 along the range, indicated on the map by the Nos. 1 to 4, and by a covering 

 of small v's. 



Commencing at the north, Nos. 1 and 2 are short, but No. 3 has a length of 25 miles. 

 Between No. 3 and No. 4, and nearly abreast of the Salt Lake City site, comes the great 

 gap of 16 miles in the Archaean. South of the gap, No. 4 has a height of 11,295 feet, 

 but just to the east of it is Clayton Peak, also Archaean, 11,889 feet. 



The rocks of the Wasatch Mountains include those of the long series from the Cam- 

 brian to the Upper Cretaceous. The Cambrian areas are lettered C ; they are the black 

 areas iinely lined with white. The Carboniferous are lettered Cb (Cb^, Cb^, Cb^) ; the 

 Cretaceous, Cr (Cr^, Cr^, Cr^, Cr*) ; the Silurian, S ; the Devonian, D ; the Triassic, Tr ; 

 the Jurassic, J. The distinguishing markings of these areas will be learned by means of 

 the lettering. 



The flexures of these rocks in the structure of the Wasatch Mountains 

 are not all the usual up-and-down flexures ; there is, besides, an in-and-out 

 series between and about the Archaean summits, as well as upon them. They 

 may be traced by following the courses of the black Cambrian areas. Com- 

 mencing at Ogden, there is first an eastward bend toward Weber, then a 

 westward, back to the summit of the mountains ; then, all the formations 

 are gathered into an east-west trough, or syncline, which heads through 

 the Gap, — the strata that lie in the Gap dipping from the north and south 

 toward its center. The head, or western termination, of the bend passed 

 the summit, disastrously to the extremity of the flexure. South of the Great 

 Gup, the Cambrian and the rest of the formations lie around Clayton Peak 



