GEOLOGICAL SURVEY OF .THE TERRITORIES. 15 



ttem. A portion of the observations made on several expeditions have 

 been given in the reports of the survey for the years 1870 and 1871. 



By examining a good map of Utah, it will be seen that the Wahsatch 

 Eange forms the eastern boundary of the great interior basin. In many 

 respects this is the most remarkable range of mountains in the interior 

 of our continent. Mr. King, in Chapter YII, Mining Industry, has 

 briefly but most graphically described "its general structure. He 

 remarks that the materials of this range are identical with the numer- 

 ous great chains of the interior basin, though developed on a scale of 

 grandeur observed nowhere else. The basis rocks are a series of alter- 

 nating layers of quartzose, mica and hornblendic schists. Above these 

 rests a heavy bed of quartzite, with very regular and marlted stratifica- 

 tion. Above the quartzite comes a bed of very hard ashen-gray lime- 

 stones, probably of Silurian age ; then a group of shales, clays, quartzites, 

 &c.; and then a great thickness of limestones, the upper portion of which 

 has been shown by the organic remains to be of Carboniferous age. In 

 the Weber CaSon and on the east side of the range from Ogden, there is a 

 large group of quartzites, i^assing up into siliceous limestones and capped 

 with a bed of red sandstone, which, so far as my own observations are con- 

 cerned, is of doubtful age, but may be Triassic. Above these comes a 

 thick group of bluish-gray limestones, with characteristic Jurassic fossils. 

 These ranges, which seem to metorun in nearly parallel lines, about north 

 and south, appear to possessa common structure and point to a common 

 origin, and cannot be treated in a comprehensive manner except by a 

 geologist familiar with the entire basin and its surroundings. These 

 ranges rise up in long, sharp ridges, apparently from the i^lains, while 

 the lowlands are covered with a group of modern deposits, which jut up 

 against the base of the mountain- chains on either side. Since the 

 crumpling, or folding, of the earth's crust, w^hich gave origin to this 

 wonderful series of mountain-chains, the erosion has been immense. It 

 is most probable that at a comparatively modern period the vast area 

 between the Wahsatch Mountains on the east and the Sierra Nevada 

 on the west was one great lake, the mountains rising up as islands in 

 this vast inland sea. The lakes, large and small, which we find scat- 

 tered over the basin at the jjresent time, are only remnants of this for- 

 mer sea. The modern deposits which cover the lowlands are mostly 

 calcareous and arenaceous beds, and sometimes reach a thickness of 

 800 to 1,200 feet, and often filled with fresh-water or land shells, indi- 

 cating a very modern origin, probably not older than the Pliocene 

 period. At any rate, the strata are all horizontal or nearly so, showing 

 that no disturbance of any great importance has occurred since their 

 deposition. These ranges of mountains extend, with greater or Jess 

 intervals In their continuity, far northward into Idaho and Montana. 

 Certain changes in the details of structure are apparent as we pass 

 northward to Snake River Basin, but there is a reojarkable similarity in 

 the rock-materials as far as the great water-divide of the continent, 

 when rather marked changes occur in the mountain-ranges of Montana, 

 where the quartzites give place to great thi(;knesses of limestones. 

 Indeed, in Montana the quartzites, which are so well shown in Utah, have 

 no existence, though far to the westward in the Salmon Eiver Mountains 

 they continue in full force. We have not the materials as yet for a 

 critical study of these remarkable folds or wrinkles in the earth's crust 

 that are scattered throughout this interior basin, more or less parallel 

 to each other. Sometimes the granitic nucleus is revealed, with the 

 unchanged beds obscurely exposed around the sides or base of the range. 

 Usually the very hard limestones have served as a sort of protection, 



