126 DELOS AND RALPH ARNOLD 
All of the evidence shows that the conditions were changing 
from boreal toward subtropical during the time just preceding 
and during the deposition of the lower San Pedro series ; but 
boreal conditions still predominated. 
This series. is placed in the Pleistocene primarily upon 
paleontologic evidence. The low percentage of extinct species 
and the occurrence of the three living echinoderms Strongy- 
locentrotus purpuratus, S. franciscanus, and Echinarachnius excentri- 
cus offers strong evidence of the Pleistocene age of this series, 
the three species of echinoderms having never been found in any 
of the beds on this coast commonly accepted as Pliocene. The 
general aspect of the deposits, the state of preservation of the 
fossils, and the unconformable position of the lower San Pedro 
series on upper Pliocene beds strengthen the faunal evidence. 
These beds are exposed in the bluffs north of Timm’s Point 
(see Fig. 2) where they rest on the brown Pliocene sandstone 
and are overlain unconformably by the upper San Pedro gravels. 
There is some doubt as to the relation between the Pleistocene 
and the underlying Pliocence in these bluffs, although most of 
the available evidence is in favor of the conformability of the 
two formations. 
Upper San Pedro sertes—The gray sandstone of the lower 
San Pedro series at Deadman Island (see Fig. 1) is overlain 
unconformably by a three-foot stratum of fossiliferous gravel 
hardened by lime, above which are about seven feet of fine sand. 
This gravel stratum and the overlying sand makes the upper 
San Pedro series at Deadman Island. The gravel stratum is 
continuous over nearly the whole of the lower, or fifty-foot, San 
Pedro terrace, and at nearly every exposure it is seen to lie 
unconformably upon the subjacent beds. This evidence shows 
that the deposition of the upper San Pedro beds followed a 
period of erosion. The best development of the upper San 
Pedro series is found in the bluff at the lumber yard north of 
San Pedro (see map of San Pedro, and also Fig. 2), where the 
alternating fossiliferous beds of gravel and sand attain a thick- 
ness of twenty feet. 
