._. - T . . 



402 



SUPPLEMENT ABY INVESTIGATIONS IN THE GRAVEL REGION. 



45°. These statements are only approximations, however, for there is considerable doubt as to the 

 position of the deep channel, whore the gravel disappears under the lava capping. There are two 

 companies interested in the Woolsey Flat gravel, — the Eureka Lake Company, which owns the 

 Boston mine, and the owners of the Blue Bank mine, which joins the Boston mine on the east. 

 As there was no work doing at the Blue Bank mine at the time of my visit, my observations 

 were made principally at the Boston mine. The channel at that point is six or seven hundred 

 feet in width. There is also some reason to believe that there is a second, or parallel, channel in 

 the Blue Bank property, but the condition of the mine prevented any satisfactory examination, 

 and I did not regard the question of the existence of such a channel of sufficient importance to 

 justify any further outlay of time. 



The only places where regular work was going on at the time I was there were at the Boston 

 mine and at the Shanghai diggings, excepting such work as Chinamen were doing at Moore's 

 Flat. 



At the Boston mine the gravel has been removed, in places, nearly to the limit of profitable 

 working by the hydraulic process, the slides of top dirt reaching nearly to the base of the steeper 

 portion of the volcanic capping, though the perpendicular bank of gravel is still, where the washing 

 is going on, a considerable distance away. I did not take any measurements for horizontal dis° 

 tances. The diagram (Plate N, Fig. 5) shows the relative thicknesses of the different strata, but 

 it is not drawn to any horizontal scale. At each fresh slide from the top of the bank large masses 

 of clay and of volcanic tufa fall to the bed-rock, where they have to be broken up, at considerable 

 expense, by drilling and blasting. It was from some of the freshly fallen masses that the speci- 

 mens, Nos. 3 1 and 32, were taken. In one of these specimens uncharred vegetable matter is 

 distinctly to be seen. After two or three more heavy slides from the top of the bank it is prob- 

 able that drifting will have to be resorted to, if mining is prosecuted any farther in this direction ; 

 though there still are large masses of gravel to the east and west to be moved by the water alone. 

 The thickness of the volcanic tufa at this point, measuring from the top of the ridge to the pipe- 

 clay, is 300 feet or more. Directly underneath the tufa there is a very large accumulation of 

 pipe-clay, or of a sandy clay, probably 175 feet in thickness on the average. The clay carries here 

 and there a few thin streaks of gravel, but is practically barren of gold. Below the clay is a 

 stratum of blue gravel, hard and compact, though not cemented, varying in thickness from thirty 

 to seventy feet. This variation is due to inequalities in the surface of the bed-rock, the upper 

 surface of the gravel being nearly level. The lower half of the blue gravel is considerably coarser 

 than the upper half, some of the boulders being as much as six or eight feet in diameter, while in 

 the upper half there are scarcely any pebbles measuring more than six or eight inches through. 

 The pay streak at the bottom contains some rather coarse gold, though in the form of flakes or 

 scales. I was allowed by the superintendent in charge of the mine, Mr. H. A. Brigham, to take a 

 few pieces of gold from the crevices in the slate near the head of the ground sluice. These have 

 been examined by Mr. Wadsworth, who says of them that " some of the larger pieces show the 

 quartz vein-stone, and are but little worn. Others are small and flattened into thin scales. One 

 shows several httle ends bent over upon the main mass. This gold, it would seem, came from 

 unequal distances, or else was freed from the matrix in the bed of the stream later, the associated 

 quartz preventing the wearing of the gold." The last remark quoted from Mr. Wadsworth receives 

 some support from the fact that occasionally quartz boulders carrying free gold are found in the 

 gravel at this mine.* 



At the Blue Bank mine the order of succession of strata is similar to that at the Boston mine. 

 The gravel has been removed so far back towards the ridge that hard lava, apparently in place, is 

 seen on the face of the bank for a thickness of seventy-five feet, and resting upon the pipe-clay. 

 Since the suspension of work the clay slides have covered up the gravel stratum to such an extent 

 that I made no special effort to get access to it. 



allow 



One boulder in particular was quite rich, and was broken up for specimens by Mr. Brigham, who generously 

 red me to select from his supply such as I wished to bring away with me. 



