42 GEOLOGICAL SURVEY OF THE TEEEITOEIES. 



that few can be obtained in a condition such as to be identified with 

 certainty. The species are not numerous, as will be seen by the list in 

 a subsequent portion of this report. At the head of Alder Gulch, a 

 Syrmgo^ora, Bhynconella, and Produotus were found, and quite a num- 

 ber of other species, which will require further study. The limestones 

 pass down into very hard cherty quartzites, and then rest un,conformably 

 on the metamorphic rocks. The strike of these limestones is about 

 north and south, bearing i^erhaps a little west of north and east of 

 south. As we have previously stated, the principal basis rocks in the 

 vicinity of this gulch are gneissic, of varied composition and texture, 

 with a higii ridge of limestone at the head of the gulch, forming a sort of 

 wall, with the outcroppings or basset edges of the strata i)ointing west 

 of north, and formerly extending in a horizontal i^osition all over the 

 surface. Eeturning to Virginia City, on the high divide, on the east side 

 of Alder Gulch, about half-way between the head of the gulch and Yir- 

 ginia City, there are i^atches of limestone, underlaid with cherty quartz- 

 ites. These isolated masses are at different elevations, sometimes upon 

 the summits of the highest ridges or down in the side gulches, showing 

 that a greater or less thickness of the underlying granitoid rocks have been 

 worn away. They also remain as remnants of the great horizontal mass, 

 2,000 to 4,000 feet in thickness, that once extended across the entire area. 

 The greater portion of the surface of the high divides, however, are 

 covered with basaltic rocks. They cap the hills, forming sort of plateaus 

 or benches, and along the sides of the gulch, show steep sides one 

 hundred feet or more in height, with the appearance of stratified layers 

 in a horizontal position. As I have frequently stated, the effusion of the 

 basalt is a modern event, probably occurring, for the most part, near 

 the commencement of our present period, after the entire surface 

 reached nearly, or quite, the present elevation. Hence we find points of 

 eff'usiou in numerous localities. The igneous lavas flowed out in layers, 

 and inasmuch as a considerable amount of erosion of the surface has 

 taken place since, the sides of some of these basaltic accumulations have 

 been worn down so as to show with clearness the edges of the different 

 sheets of basalt as it cooled. From a high elevation, one may see in 

 every direction numbers of these points of effusion. The streams which 

 wear out the gulches pass through the basalt, deep into the granitoid 

 rocks. Scattered over the surface also are patches of the Pliocene 

 marls and sandstones underneath the basalts, as heretofore. In the 

 mining districts around Virginia City, we have a thick series of stratified 

 granitoid rocks at the base, in which the precious metals were originally 

 located ; upon them rest the quartzites and limestones of Carboniferous 

 age, and filling up some of the inequalities of the surface are the modern 

 Tertiary beds; and covering all, over restricted and isolated areas, are 

 beds of basalt. The force of erosion which operated on all these rocks to 

 accumulate the vast quantities of sand, gravel, and bowlders in the gulches 

 must have been very great. Mingled with the superficial deposits are 

 fragments of all the varieties of rock formations iu the vicinity. Although 

 more or less rounded by attrition, in the great thickness of local-drift 

 may be found all the varieties of the granitoid and other rocks that are 

 sufficiently comjjact to resist the atmospheric agencies — quartzites, lime- 

 stones, with fossils, masses of basalt, &c., &c., &c. Most of these rocks 

 can be traced to their parent beds in the vicinity ; a few may seem to 

 have strayed from other districts, but the strata to which they originally 

 belonged may have occupied a restricted area, or had a local existence, 

 and thus, in the erosion of the surface, been entirely worn away, or may 

 be concealed by Tertiary or superficial deposits. In the Alder Gulcia 



