THE MARINE TERTIARY OF THE WEST COAST 609 
rather than to the Pliocene. If so, the West Coast Pleistocene 
formations have been generally folded. 
Correlation.—There has been considerable confusion in times 
past as to the proper sequence of the Pliocene. The difficulties 
appear to have been due to two factors: first, the basins of deposi- 
tion during the Pliocene were more local and isolated than they had 
Fic. 10.—Santa Margarita (upper San Pablo, Miocene) 
been during previous periods; and second, conditions of tempera- 
ture varied from one locality to another. These factors were 
undoubtedly the cause of the great differences found between the 
faunas of the various provinces; however, the latter factor, 
temperature, was the most important. The great confusion as 
to the proper sequence of the Pliocene formations is reflected in 
the numerous names which have been given to them. Beginning 
