894 IV. LINDGREN—F. H. KNOW LTD N 



parallels of 38° 30' and 39° 30'. Space forbids in this place 

 anything but a mention of the results attained. 



The early Cretaceous. — The grand features of the initiation of 

 the Cretaceous were the plication and welding of the Mariposa 

 beds with the older sediments, active eruptions continued from 

 the Jurassic period of the lofty volcanoes along the foothills, 

 then the seashore, and the intrusion, in the foundations of the 

 range, of enormous masses — batholites — of dioritic and granitic 

 magma. Of the mountain range occupying the site of the 

 Sierra Nevada at this time we know but little. The Sierra 

 Nevada and the Great Basin were evidently not differentiated. 

 A very active erosion planed down this range to a peneplain or 

 at least to a comparatively gentle topography. At this time, 

 probably shortly before the deposition of the Chico Cretaceous, 

 the first break took place, separating the Sierra Nevada from the 

 interior basin. 



The orogenic disturbance was probably of a twofold char- 

 acter. It included the lifting up of the whole region between 

 the Wasatch and the Pacific in arching form, and" a simultaneous 

 breaking in and settling down of the higher portions of the 

 arch. Thus the Sierra Nevada crust fragment was formed, the 

 larger part of which has ever since remained a comparatively 

 rigid block. Along the eastern margin the system of fractures 

 was outlined (see Fig. 2) which towards the close of the Tertiary 

 was to be still further emphasized. The faults along these 

 fractures were largely of normal character. The movement did not 

 take place evenly along all of these faults, hardly any occurring 

 in some places, while along other parts of the system the whole 

 of the fault was confined to this time. 



The main break occurred along a line extending from near 

 Markleeville by Genoa up towards Reno, and the displacement 

 reached a maximum of 3000 feet. The fault along the western 

 side of Antelope Valley, which probably will prove to be con- 

 tinuous with the Mono Lake fault, also appears to have been 

 broken at this time. But the large crust block west of this first 

 mentioned line proved too great to sustain itself, and a large part 



