HYPOGEIC WORK. 365 



the existence during this period of large freshwater lakes over the summit 

 of the mountain region ; for much rise would have made slopes that 

 would have drained the lakes (Hayden). The Wasatch and Uinta Eocene 

 basins of Utah and Wyoming, lettered with TT's and U's on the map (Fig. 

 335), were two of these lakes. Miocene lake basins, farther to the east, show 

 that even in Miocene time the progress was slow. 



Contemporaneously, similar movements were in progress over the other 

 continents: along the Andes, affecting half, at least, of South America; the 

 Pyrenees, Carpathian Alps and a large part of Europe ; the Himalayas and 

 much of Asia. 



2. The Rocky Mountain geosyncUnes. — The geanticline, above described, 

 had made little progress when local geosynclines, or subsidences, commenced 

 over the summit region of the mountains. The areas of the fresh-water 

 lakes, referred to above, were the sinking areas ; and the sinking went 

 forward, and concurrent deposition of beds, until the troughs contained strata 

 of Eocene Tertiary 8000 to 10,000 feet in thickness — the earlier half in the 

 Wasatch epoch and the later in the Green River. After these Eocene 

 basins ceased to subside, more eastern Miocene and Pliocene geosynclines 

 were formed. 



Moreover, an epoch of upturning and pUcating took place, both after the 

 laying down of the Wasatch beds and of the Green River beds ; and of up- 

 turning, in some places, after the close of the Miocene depositions. These 

 were local disturbances apparently quite independent of the great geanti- 

 clinal movement, which was also in progress. 



Igneous erujMons. — During these Tertiary movements the greatest of 

 igneous ejections occurred over the Rocky Mountain region from its summit 

 westward. It is supposed that a large part of the volcanoes of the world 

 had their birth at the close of the Cretaceous and during the Tertiary era. 



3. Faults in the Great Basin and elsewhere. — The Great Basin has many 

 bare ridges, 3000 to 5000 feet above their bases, standing in the great area 

 of lakes and alluvium-like islands in a sea. These ridges trend north- 

 ward. 



There are outcropping crystalline rocks in some of the ridges, but the 

 rocks, according to King, are mostly Paleozoic, except west of the meridian 

 of 1171° W., within 100 miles of the Sierra Nevada, where Triassic and Juras- 

 sic rocks occnr. The beds of the ridges are more or less upturned, often in 

 great anticlines or synclines, or elsewhere in simple monoclines ; but the 

 island-like isolation of the ridges prevents a study of their stratigraphic rela- 

 tions. King suggested that the more western of the ridges were perhaps 

 part of the Sierra system, which dates from the beginning of the Cretaceous 

 period, or the close of the Lower Cretaceous ; and that the more eastern 

 were perhaps post-Carboniferous in epoch of disturbance. 



Among the Basin Ranges, according to King, great anticlines characterize the Agui 

 Range, the Promontory, Gosiute, Egan, Peoquop, and Toyabe ranges ; the Humboldt 

 Range, although having a nucleal axis of Archaean ; the Pinon Range, in which the anti- 



