374: F. L. Bansome—Lava Flows of California. 



individual members. Whether some such single term as that 

 here proposed shall be used to designate the rocks midway 

 between the trachytes and andesites, or whether it will be 

 found practicable to divide them into two series, or to revive 

 the old term trachydolerite as Washington has done, may, as 

 the latter suggests, in a slightly different connection be left to 

 the winnowing action of time and usage. 



Summary. 



The contents of the preceding sections may be very briefly 

 summarized as follows : 



The area embraced by the map is a fairly typical transverse 

 strip of the middle, western slope of the Sierra Nevada, having 

 been worn down during the interval between the close of the 

 Jurassic and the beginning of the Miocene to a rough pene- 

 plain. During the Miocene the volcanic eruptions began, 

 which, accompanied by a tilting of the peneplain to the south- 

 west, continued to the end of the Pliocene. The first erup- 

 tions were rhyolitic in character, followed by the laying down 

 of a great cloaking cover of andesitic breccias and tuffs. The 

 deposition of auriferous gravels both preceded and accom- 

 panied the deposition of volcanic material. 



The accumulation of the andesitic breccias and tuffs was 

 interrupted by at least one period of considerable erosion, dur- 

 ing which a long, consequent stream, the predecessor of the 

 Stanislaus River, established its channel down the slope, cut- 

 ting down through the volcanic accumulations into the older, 

 truncated " Bed-rock series " along the greater part of its 

 course, and ultimately attaining a very regular grade. This 

 stream was subsequently displaced by a heavy flow of augite- 

 latite, the Table Mountain flow, which coming from an 

 as yet unknown source near the crest of the range, ran down 

 the stream bed to Knight's Ferry, near the edge of the Great 

 Valley, a distance of more than 60 miles. A second and 

 thinner flow followed, of augite-biotite-latite, attaining a 

 greater lateral extent, but not so long as the first flow. The 

 third or Dardanelle flow, of augite-latite, closed the series 

 of latitic eruptions. The volcanic period as a whole was 

 brought to an end by fresh andesitic eruptions, as shown by 

 andesitic breccias resting upon the latites, accompanied by 

 further tilting of the peneplain. 



During Pleistocene time the present streams have dissected 

 "the Neocene lavas and tuffs, including the latitic flows, and 

 have deeply incised the "'Bed rock series " of Jurassic and 

 older rocks. 



The Sierra Nevada latites are mineral ogically closely related 



