MESOZOIC HISTORY 335 



an idea of the character of marine conditions under which they existed. 

 The rocks themselves indicate varying conditions, as might be expected 

 during so long a period of time, but there is a striking predominance of 

 those types which denote shallow water or terrigenous origin. Quartz- 

 ites, coarse oolitic limestones, pebble-bearing and originally brecciated 

 limestones and gypsum indicate the former ; quartzites, slates, and argil- 

 laceous limestones, the latter. Pure limestones are rare and are not 

 thick ; conglomerates were not seen. In other words, deep-sea forms at 

 one extreme and shore products at the other are not in evidence. 



The sea in which these rocks were deposited probably opened to the 

 Pacific ocean on the west, as rocks of the same horizon and of very 

 similar fossil contents have been found in northern California and at 

 some intermediate points, while over eastern Nevada and western Utah 

 no post-Paleozoic marine deposits are known. The shore of the Triassic 

 continental mass may be taken as about 35 or 40 miles east of Table 

 mountain, so the conditions were evidently those of slowly deepening 

 sea, the bottom of which, at least from about 35 to 60 miles * from shore, 

 was at times so near the surface as to permit of the formation of coarse 

 oolitic limestone and limestone breccia, and at times inclosed to such an 

 extent as to allow gypsum beds to be deposited. 



JURASSIC TIME 



Some deformation and erosion probably took place at the end of the 

 Triassic, but of comparatively limited magnitude, for the Jurassic is 

 disturbed and folded and altered to about the same extent that the Tri- 

 assic is. The Jurassic continued the marine conditions of the Triassic, 

 showing a preponderance of terrigenous shales, with some limestones. 

 Ammonites, belemnites, etcetera, are common life forms. The condi- 

 tions were chiefly those of a sea (more open, perhaps, than the Triassic 

 sea) receiving muddy sediment. This is characteristic of the same 

 period in the Sierra Nevada.f 



POST-JURASSIC UPHEAVAL X 



At the close of the Jurassic period of sedimentation, this region was 

 subjected to extensive folding and was lifted above the level of the sea. 

 No trace of marine deposition from that time to the present has been 



* These are the'approximate straight-line distances of the Table Mountain and Humboldt range 

 gypsum deposits respectively from the shoreline, as determined by the limit of the Mesozoic for- 

 mations. They represent therefore minimum estimates. 



fThe Mariposa slates of the Gold Belt. 



% The youngest Mesozoic fossils found by Professor Smith in this region are Liassic, and it 

 might be more accurately termed the post-Liassic upheaval. The above term is retained, how- 

 ever, for uniformity in nomenclature, and because it is quite probable the movements were con- 

 temporaneous with those in the Sierra Nevada. 



