6 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4TH SER. 
character and distribution of the sediments of which the 
strata are composed. In the Tertiary deposits of the Mount 
Diablo range, along its entire extent of nearly 300 miles, 
there is a great variation in the character and composition of 
the constituent rocks, presenting every variety from coarse 
detrital conglomerates to two or three forms of fine organic 
shales and limestones, and alternations of these that are possible 
only under conditions far from simple. 
CONDITIONS OF DEPOSITION DURING THE TERTIARY 
During the Tertiary periods, if not during the Cretaceous, 
the physical geography of western California differed widely 
from that of the present time. In the positions of many 
present centers of stratification, constituting the main sum- 
mits of the Coast ranges which now rise with more or less 
regularity and continuity, there existed during and through- 
out the Tertiary, at least, only chains of continental islands 
grouped in similar alignment. These island masses were not 
unlike some that now exist about the borders of the Pacific 
ocean and on the coasts of Alaska and even of California. 
Among them were enclosed seas, or basins, with interconnect- 
ing channels through which the tides and ocean currents ran 
at will, thus forming an unusual variety of conditions which 
directly influenced the character and variety of the faunas of 
the time. 
Among such basins were the Great valley, the Salinas, the 
Santa Maria-Carisa, and the San Fernando valleys. But for 
the present, without attempting to make a complete statement 
of either the Coast range waterways or island groups of the 
Tertiany, it is sufficient to note only the fact that along the 
course of the Mount Diablo range six or more centers, or 
stratigraphic cores, have been recognized and to some extent 
correctly described by Whitney as the natural divisions of the 
range. These centers were to some extent outlined in the 
former paper; they deserve far more attention than can be 
given here. But while Whitney correctly observed and noted 
these various divisions of the range, its double character and 
