. Descriptive geology of Nevada south of the fortieth parallel and adjacent portions of California . ity as flg. 12, showingintrusion of overlying sheet of dacitic lava intounderlying rhyolite sands. 142 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. this point, as also at the northern end of Meadow Valley Canyon, theandesite contains considerable masses of volcanic breccia. It is con-sidexably decomposed, though not so much as the underlying rhyolite,and specimens proved to be pyroxene-andesite. REDDISH DACITES AND RHYOLITES AND ASSOCIATED SEDIMENTS. In the southern half of the northern por
. Descriptive geology of Nevada south of the fortieth parallel and adjacent portions of California . ity as flg. 12, showingintrusion of overlying sheet of dacitic lava intounderlying rhyolite sands. 142 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. this point, as also at the northern end of Meadow Valley Canyon, theandesite contains considerable masses of volcanic breccia. It is con-sidexably decomposed, though not so much as the underlying rhyolite,and specimens proved to be pyroxene-andesite. REDDISH DACITES AND RHYOLITES AND ASSOCIATED SEDIMENTS. In the southern half of the northern portion of Meadow ValleyCanyon, above the open basin to the northeast of the Mormon Range,the andesites were not observed; but the rhyolite sandstone or tuffformation was found to be overlain by beds of brown and yellow tuff,containing a variable amount of red lava, in the form of sheets. Thegreat variability in thickness of the lava sheets, and, therefore, of theinterbedded sandstones, makes a study of the series very difficult, notwo sides of the canyon ever matching; but, so far as examined, the. Scale Fig. 14.—Sketch of east side of Meadow Valley Canyon near locality of figs. 12 and 13, showingcontact of imderlying rhyolite and overlying dacite, with no rhyolite sands between. volcanic rocks found in this upper reddish series are in part biotite-hornblende-dacite and in part pink rhyolite. It is not plain in thefield whether this series of dacites and reddish rhyolites is older oryounger than the andesites, for the two are not found together; butfrom the fact that the andesite is often found resting directly uponthe basal rhyolite, it is inferred that it is probably older than thereddish dacite-rhyolite series. Between the series of red lavas andyellow-brown tuffs and the underlying series of white rhj^olites andwhite tuffs there is a marked unconformity and erosion gap (fig. 14).The dacites and reddish rhyolites not only form interbedded sheetscontemporaneous with the yello
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