16 GEOLOGICAL SURVEY OF THE TEREITOEIES. 



and are geuerally seeu in full force. In the Wahsatcli Eange some of 

 the peaks rise to the regions of perpetual snow, and on either side deep 

 and most i^icturesque canons are carved out of the solid mass into the 

 valleys below. Little and Big Cottonwood and American Fork Caijons 

 are only examples of hundreds of these wonderful canons, having, 

 on either side, nearly vertical walls 1,000 to 2,000 feet in height. 

 The Oquirrh Mountains at the south end of Salt Lake form a fine illus- 

 tration of an oblong quaquaversal, an interrupted fold or puii', with the 

 strata inclining at various angles from all sides. From Lyon Hill the 

 geologist can see the Carboniferous limestones inclining southward from 

 the south end of the range, and as he follows along the base northward 

 the quartzites, shales, or limestones which compose the sedimentary 

 group incline westward, while at the north end near the lake, the 

 strata bend around, and apparently dip under the waters.of the lake, 

 while on the east side, these beds incline to the eastward, and appar- 

 ently pass under the valley. We can see, therefore, that these valleys 

 are really synclinals, which have been excavated more or less by erosion. 

 The islands in Salt Lake are only the crests of these folds, while the 

 waters occupy the synclinal valleys ; and this remnant illustrates on a 

 small scale the scenic beauty of the great inland sea when it extended 

 over the entire basin. Ophir Caiion is one of the deep gorges carved out 

 of the west side of the Oquirrh Eange, at right angles to the axis of -eleva- 

 tion, revealing the strata on either side in a wonderfully clear manner. 

 Eegularly-stratified quartzites rest upon a series of granitoid strata, 

 which are exposed only here and there in these deep gorges. The 

 quartzites pass up into micaceous clays or shales, then gradually up into 

 limestones, in which are located some of the richest silver-mines in Utah. 

 It is quite probable that the lower beds of quartzites and limestones are 

 of Silurian age, perhaps as old as the Potsdam group, while we know 

 that at least the greater j)ortion of the second limestone-bed is of Car- 

 boniferous age. On Lyon Hill, the silver-mines are located in lime- 

 stones that are full of characteristic Carboniferous fossils. Another 

 interesting feature which tends to complicate the structure of these 

 ranges is the great number of dikes of every size. In some instances 

 the igneous matter has poured out over a considerable area. Again, it 

 has never reached the surface, as is shown only in the deep water- 

 carved gorges. In Brigham Caiion, on the east side of the Oquirrh 

 Eange, are several well-marked dikes ; also on Lyon Hill and Ophir 

 CaSou. At the north end of this range the effect of erosion is well 

 shown by the outcropping edges of the beds of. limestone that are 

 exposed on the bottom and extend even into the lake. Black rock 

 aj)pears to be a mass of Carboniferous limestone, a remnant of a bed 

 that once extended over the area occupied by the mountains, but now 

 probably dipping beneath the valley and the lake-basin. Church Island 

 is composed almost entirely of quartzites. Antelope Island has a table- 

 shaped top, which would indicate that the terraces reached as high as 

 its present summit. 



As a fine illustration of erosion in connection with these remarkable 

 anticlinal folds and synclinal valleys, we might take the Wahsatch 

 Eange from Salt Lake City northward. To the southeast and east of 

 Salt Lake City we can see, with great clearness, the deep water-worn 

 canons cleaving the mountains from summit to base, while on either side 

 are the sharp angular peaks rising up among the regions of perpetual 

 snow. Twin Peaks are among the loftiest of the range, and may be seen 

 at a great distance on either side. The caiion of the Little Cottonwood 

 is one of the most picturesque in this very picturesque region. At the 



