Vor. IIT] ANDERSON—FURTHER STRATIGRAPHIC STUDY 13 
lower sands can be followed from this point both north and 
south for several miles. They rest upon dark clay shales of 
Chico age, with which they show every evidence of uncon- 
formity. In the former paper, these beds were called, pro- 
visionally, the “Avenal Sandstones”’, although they had not 
been followed continuously from the wells at Avenal, from 
which their name was taken. . 
The Lower Shales——The next member of the series is one 
of rather unique character among the formations of the Mount 
Diablo range, chiefly on account of its purple-brown color and 
topographic effect. The shales, though sometimes calcareous 
or sandy and frequently filled with organic remains, are, on 
the whole, predominatingly clays. The calcareous portions 
are usually white lenticular masses only a few feet in extent, 
containing a variety of Foraminifera. Besides the white cal- 
careous lenses, there are usually many scattered nodules of 
barite, fragments of selenite, and often some layers of sand- 
stone. In the western part of the Coalinga field a sandy layer 
was found to contain many characteristic Eocene forms and 
some that are peculiar to the Martinez division. Among the 
_many remains of Foraminifera found in these shales, there 
are numerous tests of numuloid forms occurring either in the 
sandy layers or in the calcareous concretions. Some of the 
sandy layers also contain scattered granules resembling 
glauconite. 
On one of the tributaries of Salt creek some of the sandy 
beds contain: 
Turritella pachecoénsis Leda gabbi Conrap 
STANTON Fusus (cf. F. equilateralis WEAVER) 
Cardium cooperi GABB Cylichna costata Gasp, etc. 
Though none of these species may be exclusively of Martinez 
age, yet all of them occur in that horizon, and their presence 
does not therefore conflict with such an assignment of the beds. 
The topographic aspect of these shales is striking and ren- 
ders them easy to follow along the flanks of the range. They 
are easily reduced by erosion and therefore occupy a succes- 
sion of depressions within which the transverse drainage of 
the range converges into its larger streams. The scanty soil 
