THE MARINE TERTIARY OF THE WEST COAST 585 
2. The second factor, that of geographical isolation, was very 
probably an important one, and if so was the result of numerous 
partially isolated local basins of deposition. The sediments of 
the Tertiary were for the most part laid down in geosynclinal 
troughs which paralleled the present Coast ranges. ‘The number 
and position of these troughs has varied through the different 
periods and epochs of deposition. ‘There was therefore a condition 
similar to that which existed in the Appalachian geosyncline dur- 
ing the Paleozoic. Great thicknesses of clastic sediments, in 
aggregate exceeding 40,000 feet, were deposited on the West 
Coast during Tertiary time. These Tertiary basins existed either 
as large embayments or long inland seas, some of the latter of which 
were comparable in size to the Mediterranean and were probably 
nearly as well separated from the main ocean basin. ‘These con- 
ditions produced marked local environments, with corresponding 
local changes in the faunas. It is very probable that the faunas in 
each basin derived certain peculiar characteristics due to isolation 
alone. 
3. Still another factor that has brought about difficulties in 
correlation in the West Coast Tertiary has been the rather general 
poor preservation of the fossil material. The Tertiary beds have 
been extensively folded and tilted, and this deformation has resulted 
in the leaching of the original material of the shells, especially in 
the sandstones and shales. Intensive collecting will in time remedy 
this difficulty as well as bring to our knowledge a larger number of 
localities where the fossils are in a better state of preservation. 
In presenting a correlation table of this kind, one of the first 
things that will be asked is the author’s point of view in attacking 
the problems. The point of view accepted is that diastrophism is 
the fundamental basis for differentiating geologic divisions. In 
other words, the divisions recognized in this paper have been made 
on the basis of stratigraphic breaks which are believed to be more 
than local. It is important to note that every stratigraphic unit 
thus recognized is also represented by a distinctive fauna. 
The paleogeographic maps presented in this paper are not 
accurate in detail and will undoubtedly be modified by future 
work. The present knowledge of the geology of the Coast ranges 
