AMARGOSA RANGE, SEDIMENTARY ROCKS. 
contemporaneous with the quartz cement, which secondarily enlarges 
the clastic grains of quartz. Mashing, beside- developing sericite, 
has locally elongated the pebbles of the conglomerate, forming 
schistose conglomerate. 
The more impure quartzite grades into slat \ ales and schists. 
The shales are fine grained and of a greenish or dark-gray coL 
laminse from one-sixteenth to one-half inch thick. The slaty shale has 
usually a few muscovite plates on its parting planes and passes, with 
gradations, into fine-grained bluish or greenish-gray sericite schists. 
The schistosity is usually parallel to the original bedding of the rock, 
but in places cuts it at all angles. In the schist deep-red garnets, 
small tabular hexagonal greenish plates (ottrelite), greenish-gray 
micaceous aggregates (chlorite), or grayish prisms (andalusite) are 
developed. Under the microscope these schists appear without orig- 
inal structures. Fine shreds of sericite, with chlorite, in some thin 
sections are well aligned parallel to the schistosity, and between Mich 
bands are fine mosaics of quartz and a little orthoclase. Among the 
phenocrystic minerals of the series, clearly of later origin than the 
groundmass, are staurolite, andalusite, ottrelite, biotite, chlorite, gar- 
net, ilmenite, and magnetite. Zircon, graphite, and rutile are present 
locally. Small crystals of tourmaline, cutting the schistosity in all 
directions, are present in most of the thin sections. The occurrence 
of this mineral 10 miles or more from the nearest granitic outcrop 
possibly indicates the presence of a considerable body of granite be- 
neath the Amargosa Range. The interbedded marbles are fine- to 
medium-grained rather dense rocks, of buff, pink, purple, gray, or 
white color. Much of the marble is finely laminated. The presence 
of clastic grains and small pebbles of quartz and of cross-bedding 
indicates that the original limestone was deposited in shallow water. 
Through metamorphism not only has the rock been thoroughly re- 
crystallized and locally someAvhat silicified, but muscovite has been 
developed on the parting planes, and calcite veins, cutting it in all 
directions, have been formed. 
Interbedded with and sending short arms out into the schist at 
Poison Spring are thin discontinuous sheets of hornblende gneiss. 
composed of a fine mosaic of quartz and feldspar, with much fibrous 
greenish-black hornblende and in certain bands red garnet. Under 
the microscope the mosaic is seen to be composed of quartz, ortho- 
clase, and plagioclase. In the mosaic are large skeletons of horn- 
blende, garnet, zoisite, and titanite. Apatite and magnetite are pres- 
ent as accessory minerals. Chlorite is secondary to hornblende, 
sericite, or kaolin, and calcite to the feldspars, and zoisite to the i 
tual alteration product of hornblende and plagioclase. A sheet of 
hornblende schist cuts across the bedding planes of marble and schis 
at a low angle 200 yards west of the Chloride Cliff camp, nea 
