Quaternary Deposits . Etc. — Mills. 347 
tion of a basin eroded from hard feldspathic porphyry. The 
bottom of the pool, at the lowest point, is seven and a half 
feet lower than the rocky lip at the outlet. To test the loose 
materials on the bottom of the pool for gold, the water of the 
stream was carried around the pool in a canal, and the water 
in the basin lowered by cutting down at the outlet and by 
pumping until a large portion of the floor of the pool was laid 
bare. 
Over a part of the floor the rock is bare, and over a part of 
it the surface of the rock is covered with sand and gravel and 
large fragments of porphyry. At the head of the pool there is 
gravel or cascalho which has evidently been brought down and 
deposited there by the stream; but other patches of cascalho 
were evidently formed from quartz veins in place there, and 
these pass with the outcrop of the veins under the loess on 
the banks. The pool bends at nearly a right angle. One 
strip of cascalho crosses the pool near its outlet, continues on 
the left bank to the pool above the bend, and crosses it there 
again. On the bank this cascalho was naturally overlaid with 
loess, but the loess has been excavated, and the cascalho has 
been washed for its gold. It is also gold-bearing on the bed of 
the pool, or rather so much of it as is left, for a considerable 
part of it was excavated and washed while I was on the ground. 
The cascalho of this sheet or strip is evidently from some 
small, irregular quartz veins which exist there in the porphyry, 
and the outcrop of which extend along with the strip of cas¬ 
calho. Other patches of cascalho accompanying quartz veins 
occur on the bed of the pool, and pass with the outcrop of the 
veins under the loess on the banks. Near the quartz veins the 
rock on the bed of the pool is softened, and in the canal the 
softened rock was exposed to a depth of 12 or 15 feet, while 
over the greater part of the floor of the pool the rock where 
exposed was hard. The softened rock near the quartz veins 
was colored with iron oxides, and the softening was undoubt¬ 
edly due to the decomposition of pyrites which accompanied 
the quartz and gold. 
The cascalho is gathered in places around large fragments of 
porphyry evidently not far removed from where they were in 
place. The sheets of cascalho are generally but a few inches 
thick, rarely more than eight inches, except in furrows of the 
rock where the gravel is at times eighteen inches thick, and in 
