342 University of California Publications in Geology [Vol. 8 



lacustral surface. This is indicated by the fact that the lacustral beds 

 abut against, as well as lie upon, the worn igneous-rock surface along 

 the north base of the hill. The lacustral beds are not upturned at 

 the contact. Farther south much of the hill is capped by basaltic 

 lava, of which there were apparently two flows. The lavas are prob- 

 ably younger than the lake beds, as they appear to overlie them at a 

 point two or three miles south of the Orizaba mine. The pre-lava 

 surface of the underlying rocks appears to have possessed gentle relief. 

 The lavas lie nearly horizontal at the summit of the hill, but on the 

 east side they apparently dip quite steeply eastward under the valley. 

 The northern end of the hill, along the road between Bell Spring and 

 Black Spring, consists of granular rocks, in which the abundant min- 

 erals are plagioclase and orthoclase feldspar and biotite, with little 

 or no quartz. Pegmatite and aplite dikes cut these granular masses. 

 The smaller patches of pre-lacustral rocks lying farther north in the 

 middle of lone Valley also consist of lavas and granular rocks. 



On the west side of Stewart Valley, west of Stewart Spring, a 

 few small patches of black lava protrude through the lake-beds ; they 

 lie at a considerable distance from the base of the Gabbs Valley Range, 

 which rises from Stewart Valley on the west. 



The occurrence of these outcropping masses of pre-lacustral rocks 

 in both lone and Stewart valleys has a bearing on the question of the 

 thickness of the Esmeralda beds lying in these valleys. 



ESMERALDA FORMATION 



West, north, and east of Cedar Mountain, in Stewart and lone 

 valleys, are extensive exposures of a set of lacustral and intercalated 

 terrestrial strata. These beds are considered to be the equivalent of 

 the Esmeralda formation 4 described by Turner from the Silver Peak 

 Range forty miles to the south. 



In defining the Esmeralda formation Mr. Turner stated in part: 



In Esmeralda County, Nevada, there are extensive deposits of Tertiary 

 sediments which contain, at some points, abundant plant and animal remains. 

 This series may be designated the Esmeralda formation, taking its name from 

 the county in which it occurs. Near these lake deposits, at the north end of 

 the Silver Peak range, there are beds of coal, and the first published notice of 

 these Tertiary beds appears to be that of the mining engineer, Mr. M. A. 

 Knapp, describing particularly the coal deposits. Mr. Knapp collected some 

 molluscan remains near the coal beds, and these were examined by Dr. J. C. 

 Merriam, of the University of California, who considered the shells indicative 



* Turner, H. W., The Esmeralda Formation, American Geologist, vol. 25, p. 

 168, 1900. 



