52 OSCAR 7. HERSHHEMV 
shows the smoothing and rounding action of the glacier up toa 
certain height, above which the bare rock is extremely rough 
and jagged. Some glacial grooves are seen and a little striation. 
In another place there is a well-defined line of perched erratics. 
This glacier also issued from the high mountains, and it cut 
directly thru the old Miocene river channel, carrying its huge 
granite bowlders nearly or quite to the Minersville-Trinity 
Centre road, terminating at a point probably now no greater than 
3000 feet of altitude. Itis a well-known fact that all the gulches 
which are cut into this old Miocene channel deposit have been 
rich in placer gold, except the valley of the East Fork, which 
cuts directly thru it, and yet never paid to work. The apparent 
anomaly is explained when it is understood that the East Fork 
glacier ground all of the gold-bearing alluvium out of the valley 
, and left in its place its own only slightly auriferous deposit — 
the glaciated valleys are never worked as placers. 
Quite a number of other valleys in the Sierra Costa Moun- 
tains were once occupied by glaciers. The presence of a number 
of lakes (as mapped) in the deep canyons south and east of Mt. 
Thompson of the granite Cariboo range seem to indicate that a 
cluster of them occupied that region. Probably a score or more 
existed in Trinity county alone; but the examples given in this 
paper are typical of them all, and will suffice for the purposes of 
the present study. 
AMsis, AVES, (ON ANSUS, (CILACINTINS) 
At one time I thought I had detected evidences of two glacial 
epochs in the Sierra Costa Mountains, one very recent and 
another much older, but I have had to revise this opinion. The 
deposits near the lower end of the glaciated valleys are of 
slightly more aged appearance than those near the heads, but 
the contrast is not great. They are essentially a unit, so far as 
age is concerned. 
The weathering of the once striated, polished, and perfectly 
smoothed rock surface, the erosion of small canyons in the rock- 
floors of several of the glaciated valleys near their heads, and 
