24 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4TH Ser. 
The faunas of the foregoing lists are generally character- 
istic of the Coalinga beds. Above these fossiliferous beds 
the formation is chiefly sand with little or no appearance of 
fossils. 
To the south of Coalinga, or of the Warthan creek, the con- 
glomerates and the associated oyster beds do not form a con- 
spicuous feature of the formation, and in fact have not been 
directly identified. This is probably due to the fact that 
these beds were greatly thickened by the addition of 
sands during the time that an open channel connected 
them with the sea to the westward, causing conditions 
not favorable to the life and growth of oysters, but favor- 
able to the development of some species not often met with 
elsewhere. 
Along the Jacalitos creek the thickness of the Coalinga 
beds has been estimated at 1100 feet. There is an appearance 
of unconformity between the Coalinga beds and those above, 
while the line separating them from the beds below is not 
definitely established. Along the various branches of the 
Zapato Chino creek and eastward the Coalinga beds thicken 
still more until they attain an aggregate of 1500 to 1600 
feet. They rest upon the white or rusty brown beds of the 
Monterey shales, with which there is little to mark an uncon- 
formity. As the Monterey shales here become sandy in their 
upper portion, the change from them to the Coalinga is not 
so abrupt as in the field farther north. There is not a great 
variation of lithological characters in the Coalinga as seen 
along the range south and east of the Warthan creek. There 
is, however, near the middle of the series, a bed of white 
volcanic ash from 12 to 16 feet thick, which is in some places 
conspicuous, but which is not always found, or at least is not 
always recognizable. It can easily be followed for three or 
more miles southward from the Warthan creek, a little east 
of Alcalde, and it appears again on the west fork of the 
Jacalitos at the Roberts ranch and also on the eastern tribu- 
taries of the Zapato Chino, on the Kreyenhagen ranch. Near 
Alcalde it is immediately underlain by a fossiliferous bed from 
which the following species have been obtained : 
