SRODIPS ANOLE NEOCENE OF CALTRORNTA. 449 
below marine deposits of later date. (See Plate X.) They make 
up a considerable portion of the level plain surrounding the bay 
as shown by recent stream cuttings. These deposits have yielded 
remains of the mammoth or mastodon, and in the deposits in the 
various streams running to the bay are found a large number of 
trunks and cones of conifers, sometimes four feet in diameter. 
The third class are recent marine deposits. On the ocean 
side these are very marked, forming the top of the level benches 
described and having a thickness in the sea-cliffs of from five to 
fifty feet, in one place just south of Mussel Rock, having a thick- 
ness of over 200 feet. In some places, as near Monterey light- 
house, the beds are only a foot or two thick, and are made up of 
black earth, rocks, and abalone shells in great numbers. On the 
bay side of the mountains the surface of the broad valley plain 
and stream benches is the result of marine erosion and deposition. 
The deposits there are seldom more than a foot or two thick. 
Here are also found large areas of black earth full of rocks and 
shells. 
fiistory.—The interpretation of these data would seem to be 
as follows: ; 
1. A period of erosion with the mountains about 1800 feet 
below their present level. This may have been the final position 
of the mountains at the end of the post-Merced movement, or 
the mountains may have shifted to this position soon after. 
During this time the most of the soft Merced series above the 
water line seems to have been removed, the water acting asa 
protection to the deposits which now fringe the base of the 
mountains. 
2. A period during which the mountains stood about 1200 
feet higher than during the first period, or about 600 feet below 
their present level. This produced the marked bench or plateau 
forming the summit of the foothills. 
3. A period during which the region stood, according to 
Professor Lawson," nearly 400 feet higher than at present. San 
Francisco Bay was a broad valley and the islands stood up as 
t Univ. of Cal., Bull. Dept. of Geol., I., 267. i 
