STRATIGRAPHY OF SOUTHERN CALIFORNIA 27 
The deposits of the upper beds in the vicinity of San Pedro 
consist for the most part of coarse gravels and sands which 
show alternating dune and water bedding, and have the appear- 
ance of having been laid down during a period of rapidly chang- 
ing conditions. 
The fauna of the upper beds is southern in character, and, 
as would be expected, approaches more nearly the present living 
fauna of the San Pedro region. Since the fauna of the upper 
beds inhabited shallower water than that in which either the 
Pliocene or lower San Pedro faunas lived, one would expect to 
find in it fewer of the cold water forms and more of the species 
found between tides and in the warm shallow waters of lagoons. 
Such is the case, but further, it is a noticeable fact that in the 
upper beds over 14 per cent. of the fauna are species which are 
now found living only south of San Pedro. This is not only 
true, but of those species found in the upper beds which are still 
living at San Pedro, a great majority are forms which are com- 
moner in the waters south of that place. 
. Although over 6 per cent. of the upper San Pedro fauna are 
found now living only north of San Pedro, these northern species 
are only very rarely found in this formation. On the other hand 
most of the distinctly southern forms and those which, though 
now living at San Pedro are commoner further south, are com- 
moner in the upper beds, thus giving it a semitropical aspect. 
Such species as Cardium elatum, Arca labiata, Pecten dentatus, 
Mactra exoleta, Venus gnidia, Murex leeanus, Eupleura muriciformis, 
Cancellaria tritonidea, and Bulla punctulata give this fauna its 
southern character. The evidence afforded by the southern 
forms outweighs the evidence of the northern species in another 
respect, for it would require a great change in conditions from 
those prevalent during later Pliocene times to cause these south- 
ern species to migrate northward to the San Pedro region; while 
this same change in condition would not so materially affect the 
northern species, for they could simply migrate into deep water 
where the conditions would more nearly approximate the boreal. 
This latter has been the case with such species as Lucina acuti- 
