390 
TURNER. 
Pleistocene lake, formed by the damming back of waters by 
the later andesite. Further evidence on this point will be 
presented in a succeeding paragraph. 
Southeast of the Sulphur Spring House, in the southern 
part of Mohawk Valley, is some sandstone sufficiently con¬ 
solidated to be used for chimneys. This hardening of the 
material has probably been brought about by the cementing 
action of the waters of the adjacent springs. Some of the 
sandstone shows plant impressions. The sandstone is 
bedded nearly horizontally. Just east of the sulphur 
springs there is a disturbance in the lake beds, the dip being 
southwest 22°. 
About one-fourth mile north of the Sulphur Spring House, 
on the north bank of a little stream, is an exposure of lake 
beds, which dip westerly about 13°. The material is rather 
fine detritus. A microscopical examination of a whitish 
layer showed sand grains, fragments of volcanic glass, green 
hornblende, biotite, apatite, and black opaque grains, pre¬ 
sumably magnetite. The volcanic glass appears to be rhyo¬ 
litic ; the sand grains, hornblende, biotite, and apatite are 
probably from granite. 
The narrow area of river gravel to the north of the lake 
beds and directly connecting with them has at first sight 
the appearance of being the bed of a former outlet of the 
lake, but as some of this gravel lies at an elevation of 5,500 
feet this does not seem likely. There are indications of local 
disturbances here, in the form of little benches, such as are 
to be found where land slides have taken place. It is prob¬ 
able that the low position of part of this gravel just to the 
north of the mouth of Cedar Creek is due to subsidence by 
a land slide. This river gravel seems, on the map, Plate 
No. 4, to rest on andesite, but this is not the case, the rock 
underlying the gravel being of the auriferous slate series. 
Pliocene Beds. 
There are some beds exposed along the middle fork of the 
Feather River, a little to the east of Mohawk Valley, on the 
ranch of Abel Jackson. These beds consist of sandstone 
