68 University of California Publications in Geology [Vou.7 
forms, in its flightless character suggesting to the author of the 
species an insular breeding-ground free from enemies, and 
finally in the fact that the accompanying mollusean fauna in- 
dicates a climate cooler than that which characterizes the region 
at present. It is regretable that a larger number of species was 
not discovered in the same horizon. 
PLEISTOCENE Fauna 
Potter Creek Cave.——Potter Creek Cave’ takes its mame 
from its location on Potter Creek, about one mile east of Baird, 
a station of the U. S. Bureau of Fisheries on the MeCloud River 
in Shasta County, California. The locality lies at present in 
the lower Transition zone at an elevation of 1500 feet above the 
sea. The surrounding country is well timbered with conifers, 
oaks, and maples in the main, and with lower serub forming 
thickets in less favorable exposure. Topographiecally the region 
is rendered rather rough by numerous small tributaries of the 
MeCloud River cutting through the Baird Shales, and the 
McCloud Limestones, to form cafons with abrupt slopes and 
much dissected ridges. The cave ocetpies at present a position 
800 feet above the McCloud River, only slightly over a mile away. 
According to the observations of Sinelair, the river flowed 
during the formation of the cavern deposits at approximately 
the level of the cave floor. The lowering of the river bed and 
the backward cutting of tributary streams brought about more 
rapid drainage of the country to either side of the cave, less 
water entered the fissure, and cave-cutting ceased. Openings 
were formed later in the roof of the cave by surface erosion, 
thus permitting the entrance of clay, rock fragments, broken 
bones and possibly of live animals. Subsequent uplift increased 
the cutting by streams in the region, and Potter Creek eut 
down through one of the galleries, thus forming the present cave 
entrance. 
There were two or three of these periods of uplift as deter- 
mined by Sinclair which changed the character of the country 
from one of moderate relief to one of mountainous aspect dis- 

8 See Sinclair, W. J., Uniy. Calif. Publ. Am. Areh. Ethn., vol. 2, pp. 
1-27, 1904. 
