396 SUPPLEMENTARY INVESTIGATIONS IN THE GRAVEL REGION. 
in length, extending from shaft No. 9 to the present high bank at the west end of the mine, besides 
a considerable extent at places on the southern rim. The rock is nearly level for three or four 
hundred feet, measuring across the channel from rim to rim. It is worn smooth, but does not show 
such striking forms as are to be seen at Smartsville, and there are frequent irregularities on the 
surface and knobs rising to the height of fifteen or twenty feet. 
The high banks are from about 220 feet to 340 feet in height. The blue gravel, not much cemented, 
is about 130 feet in thickness. A striking feature of the Malakoff banks is the distinct stratifica- 
tion of the material,* which is made more noticeable by the occurrence of large bodies of pipe-clay, 
with intercalated red gravel. The clay is in some places as much as 150 feet thick. It falls in 
large blocks, and has to be broken up, like the rock boulders, with powder and sledges. The clay 
strata seem to have the same grade as the underlying gravel and bed-rock, but it cannot be said 
positively that they would show this character for any great distance. <A great difficulty in the 
way of settling such a question is the constant removal of the exposed faces, and the absence of 
any records to show just what position the clay formerly had. At some distance above the heavy 
stratum of clay just referred to, another thick mass of the same material appears coming to view as 
the high banks are worked away to the north and northwest towards the lava ridge. The top 
gravel at Malakoff is mostly quartz, while the lower strata contain many varieties of rock and 
boulders. These latter are not so much worn and rounded as similar boulders are lower down the 
ridge. 
In some parts of the mine the banks show a capping of volcanic material to a thickness of from 
two to twenty feet, but, in general, the gravel capped with tufa has not yet been reached. 
The material is very easily moved by the hydraulic stream ; indeed, sometimes it moves too 
easily. There is a constant dropping of fragments from the bank, and sometimes a slide which 
seriously interferes with the regularity of the working. 
In addition to the main excavation, to which the preceding notes refer, there has been a large 
extent of top gravel removed to the south and west, both on the ground immediately adjacent to 
the Malakoff mine and farther down towards Lake City. Where a top bank has been long exposed 
to the weather the surface is grayish white in color, and very brilliant when illuminated by the 
bright sunlight. 
I could not find any map of these outlying pieces of ground, nor learn of any measurements 
which could be used as a basis for calculating the amount of material already removed or yet to be 
removed from them. The surface of the property owned by the North Bloomfield Gravel Mining 
Company has been surveyed with great care, and laid off in small sections in such a way that it 
will be a comparatively easy matter to determine the number of cubic yards removed and the 
average yield per yard from year to year. Partial data of this kind are given on page 70 of Mr. 
Bowie’s paper on “ Hydraulic Mining in California.” It is there stated, on the authority of Mr. 
Perkins, that for the years 1874-75 and 1875 — 76 the yield at the ‘‘ No. 8 Claim” was respectively 
3.9 and 6.6 cents per cubic yard. 
The top dirt or volcanic tufa and the pipe-clay are barren of gold, though the latter is inter- 
stratified with thin layers of washed gravel which contain more or less of the precious metal. 
These thin auriferous layers amount in the aggregate, in the thickest stratum of pipe-clay, to as 
much as fifteen or eighteen feet, or from ten to twelve per cent of the whole thickness. There are 
not many large boulders at Malakoff, excepting on the surface or near the bed-rock. The boulders 
seem to be comparatively few in number; though, as it is the custom at this mine to blast the 
boulders and blocks of pipe-clay and run them through the sluice and tunnel, it is not easy to form 
any good.estimate as to their relative quantity. 
The underground explorations carried on from the Malakoff Company’s Prospect Shaft No. 1, 
which is distant about half a mile from No. 8, make the grade for that distance about 125 feet to 
the mile, somewhat greater than the grade from Malakoff to Badger Hill, but not so great as that 
from the same point to Woolsey’s Flat, as will be seen in what follows. 
* See ante, Plates A and I. 
