136 DELOS AND RALPH ARNOLD 
the writers after a study of the stratigraphy and faunas of the 
formations under discussion. The San Diego formation, with 
which are correlated the Deadman Island Pliocene and the Santa 
Barbara (Packard’s Hill and bath house beach) formations are 
placed in the upper part of the Merced for the following rea- 
sons: (1) the strata of the Merced series wherever examined 
by the writers show much more contortion than the strata of 
the San Diego formation or its equivalents; (2) the fauna of 
Deadman Island Pliocene grades over by easy stages into the 
fauna of the Pleistocene with only a slight break between the 
two, thus precluding the possibility of the intercalation of such 
a distinctive fauna as that of the Merced series between the 
Deadman Island Pliocene (equivalent of the lower San Diego 
formation) and the San Pedro series (Pleistocene) ; (3) the occur- 
ence in only the very uppermost layers of the Merced series of 
Echinarachnius excentricus, which is found in the upper horizon of 
the San Diego formation; and the total absence of the common 
Merced echinoderm, Scutella interlineata, from the San Diego 
formation and all of its equivalents and overlying beds; (4) 
the abundance at the very bottom of the San Diego formation 
(in the lowest part of the San Diego well section only) of the 
typically characteristic middle Merced pelecypod Arca schizotoma 
Dall (=A. sulicosta Gabb). 
The probability of an overlap of the time periods represented 
by different formations, Merced, San Diego, and San Pedro, is 
considerable; in fact the term Merced series, as used by Law- 
son, probably includes nearly, if not all, of the San Diego 
formation, and probably part of the San Pedro series. 
The following correlation table gives the relation between 
the different formations of the Pliocene and Pleistocene of the 
coast of California as understood by the writers. 
CONDITIONS PREVALENT DURING THE PLIOCENE AND PLEISTOCENE. 
Basing the conclusions upon the evidence offered by the 
faunas of the Pliocene and Pleistocene formations it is seen that 
there has been a fluctuation of conditions along the California 
