728 DESCEIPTIVE GEOLOGY. 



the sedimentary strata, and, as it is a somewhat exceptional occurrence, de- 

 serves special notice. On a superficial examination, it resembles the dolerites 

 breaking out along the base of the range ; but a careful study in the field 

 suggests, at least, that it is an older rock allied to the dikes found cutting 

 the Archaean bodies of Western Nevada. Under the hammer, it is an 

 exceedingly tough rock, breaking with a fine, hackly fracture, quite unlike 

 basalts with globulitic base. It is a medium-grained crystalline aggrega- 

 tion of brilliant, needle-like feldspars and augites, no other mineral being 

 recognized by the unaided eye. The microscopical study of this rock 

 throws considerable light upon its geological relations, and reveals at once 

 the jDresence of quartz-grains with liquid-inclusions, being, as Professor 

 ZirkeP remarks, " an ingredient which has never been observed in any dole- 

 rite or basalt in the world ". The rock recalls many varieties of the diabase 

 of Northern New Jersey and Connecticut. 



On the east side of the main anticlinal axis, which crosses the range 

 obliquely at Spring Valley Pass, the quartzites of the Koipato series are 

 seen to have a strike parallel to those on the opposite side, namely, about 

 north 30° east, but dipping to the east 30°. These quartzites have not the 

 same lithological characteristics as those which underlie the limestones at 

 the mouth of Star Canon, but are more purely siliceous, thinner-bedded, 

 and more irregular. Passing north from Spring Valley Pass, along the east- 

 ern foot-hills, a small hill of limestone lies at the entrance to Indian Canon, 

 dipping easterly. Still farther north, other isolated patches occur in the 

 region of Cottonwood Canon, with the same dip, indicating the eastern side 

 of the fold. From these limestone beds, a portion of a large belemnite was 

 secured, which Prof. F. B. Meek has described under the specific name of 

 Belemnites Nevadensis. 



South of Spring Valley Pass, the foot-hills are formed of dark lime- 

 stones, which overlie the quartzites. They also strike north 32° east, and 

 dip 45° to the east. From this point southward, the Star Peak beds thicken 

 rapidly, and for 8 miles the hills are covered by heavy masses of dark lime- 

 stone, in which are found a few well-preserved fossils of the genus Am- 

 monites. The deeper canons, as Buffalo Canon and others, erode through the 



^Microscopical Petrography, vol. vi, 101. 



