98 



THE AUEIFEEOUS GEAVELS OF THE SIERRA NEVADA. 



those of granite are exceedingly rare. There is in the hank at this claim a great deal of opal, 

 almost all of which is green, a part of it being of a bright emerald color. The boulders in the bank 

 are almost entirely undecomposed, and the opal occurs in the interstices between them. 



x\t Blacksmith. Flat, on the south side of the ridge between Long Canon and the Middle Fork 

 of the Middle Fork of the American Eiver, the maximum thickness of the gravel exposed in the* 

 hydraulic banks is fifteen feet. The gravel is here and there overlain by an irregular stratum of 

 sand ranging from five to ten feet thick. Above this come several hundred feet in thickness of 

 volcanic materials forming the crest of the ridge. The gravel is smoothly rounded and made up 

 of a great variety of metamorphic rocks, with a large admixture of granite boulders, some of which 



For a distance of two or three miles above Blacksmith Flat the 



are eight or ten tons in weight. 



ditch, which runs 300 feet above the bed-rock, is cut through gravel, and there are indications at 

 other localities that the quantity of gravel in this ridge between Long Canon and the Middle Fork 

 of the Middle Fork of the American Eiver is very considerable, although at the same time the 

 capping of volcanic materials along the central portion of the ridge is very heavy. 



At Castle Hill, near Georgetown, the gravel varies, in the channel, from one or two inches to two 

 or three feet in thickness, and. contains some pretty well washed quartz pebbles, with many frag- 

 ments of bed-rock. It is immediately overlain with volcanic cement, which is generally grayish in 

 color. This volcanic capping is probably 125 feet deep on the crest of the ridge J and it contains 

 many large boulders, which, are equally plentiful towards the top or the bottom of the mass. 



At Centerville, some ten or twelve miles below Georgetown, the material called gravel consists 

 mostly of angular fragments of the bed-rock, of all sizes. Among the great variety of dioritic, 

 hornblendic, and porphyritic rocks of which this gravel is made up, there are a few of granite, and 

 these are well rounded*. Numerous quartz boulders also occur, many of which are very large, 



him from eight to fifteen tons. The greater portion of these boulders, whether 



some even weig 



One 



wan; uvuu v.v,.^..^.-, *-.^~~ — p — ~- — -- ^ 



lame or small, are but little rounded by water, although some of them are thoroughly so. 

 large boulder of compact white quartz found here yielded $ 8,000 in gold, and others have also 

 proved valuable. The bed-rock at this place is chiefly slate, but there are dioritic rocks farther to 

 the southwest, in the sides of Pilot Hill. The bed-rock slopes to the Fast and the West ; and on 

 the eastern slope there is a certain area covered with a few feet in depth of well-washed gravel, 

 which is very firmly cemented together and very hard. This gravel is overlain by the brecciated 

 mass ten to twenty feet thick, which is the ordinary -gravel" of the district, and which is in all 

 probability only a local deposit, perhaps accumulated from the slopes of Pilot Hill. 



The general character of Buffalo Hill, near Georgetown, is much like that of Mameluke Hill ; the 

 crest of the ridge runs for half a mile, or more, in a direction N. 18° W. (magnetic), between West 

 and Illinois canons. It is capped with volcanic bouldery cement, in places a good deal decom- 

 posed, and with a maximum depth of from seventy-five to eighty feet. There appears to be, in 

 general, but little graved on the bed-rock, beneath the cement; and, although numerous shafts 

 have been sunk here, the results do not seem to have been pecuniarily satisfactory. 



At Tipton Hill, two and a half miles a little west of south from Kentucky Flat, the gravel 

 ranges from four to six feet in thickness, and is almost entirely made up of quartz, in fragments of 

 moderate size, not much rounded. This gravel is covered with the ordinary bouldery cement, and 

 the maximum height of the banks is about thirty-five feet. 



At the Excelsior Claim, near Placcrville,* the maximum height of the bank is 170 feet, of 

 which the lower sixty or seventy feet are " pay gravel " consisting of quartz, metamorphic rocks, and 

 sand • the upper hundred feet is made up of well-rounded and water-worn volcanic gravel. This 

 is said also to contain a little fine gold. The line of demarcation between the pay gravel and the 

 volcanic capping is pretty well defined, the former being yellow, and the latter bluish-gray. There 

 are a few metamorphic pebbles in the volcanic beds ; but no volcanic materials in the pay gravel. 

 About twenty acres of ground have been washed off here, with an average thickness of something 

 over fifty feet of "pay gravel." Along the northern side of Hangtown Hill, just south of Placer- 



• For the position of the localities and the claims about Placerville, see diagram, Plate C. 



