LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

4 LOWER CRETACEOUS DEPOSITS IN CALIFORNIA. AND OREGON
Creek. From the latter stream the belt extends in a southwest course to
Dry Creek, northern Tehama County, and thus across the delta area.
On the North fork the beds have a thickness of about 3480 feet, but they
thicken rapidly toward the southwest and occupy a correspondingly
broader zone. On Dry Creek, a few miles south of the delta axis, their
thickness is about 8400 feet, and their zone is not less than 4.2 miles broad,
measured across the strike. Farther south the beds become thinner and
their sone narrower, On McCarthy Creek, the thickness is 7660 feet, and
the zone has a breadth of 2.5 miles, but the angle of dip is somewhat
greater.
The basal conglomerates of the Horsetown group are for the most part
lenticular, although on the whole they form a fairly well defined geological
and topographical belt which extends for many miles through tbe Cottonwood
district. In the lower part of this belt, as at Ono, is the earliest
faunal zone of the Horsetown group, namely, tbe Ono zone. Its fauna is
for the most part quite distinct from tbat of the Paskenta group and is
well represented near tbe bridge on the North fork at Ono, Locality 1353
(Calif. Acad, Sci.), and at the same horizon on Eagle Creek, half a mile
east of the bridge. The following composite list of species from these
points represents less than 200 feet of strata:
Lytoceras ira&ki nov. Luloeeras aulaeum nov.
PhtjUoceran occidenlalt nov. Neocra&ptditc* afiifia nov.
Crtoeefan latum Gabb IJoplacrificerat remtmdi (Gabb)
j4m>(eu(At« onoerms nov. AcrotcufAui kememit nov.
Inoeeramua COJOTHCU* nov. Plicutuia varia Gabb
I. emtoides nov. Nemaden fcreweriana (Gabb)
Pleuromya papyrarea Gabb Aitarte ealifarntca Stanton
P. rtjUumbonoto nov. Corbula fihta Stanton
-dpArwftna of, nilida (Gabb) Petien (jSj/n^ctoncma) Bp.
Ampullina avdlana (Gabb) Nerinm arc.ki'medi nov.
Potamidti diatkrw Gabb JVrbo fetlivvm nov.
Tittarolax bicarinata (Gabb) DtasComa cccidentaiia Stanton
Only a small number of these species appear in the Paskenta group in
the Cottonwood district; a few others occur in it in its type district and on
tbe Cold fork of tbe Cottonwood, near Stephenson's.
Where this zone crosses Roaring River it is not directly recognisable,
but its position is indicated by fossil zones found above and beneath it
and by basal conglomerate beds, as is tbe cose farther south. This zone
is not younger than early Hauterivian, as evidenced by the presence of
Neocraspedites aguila, HoplocrioccraA remandi, Ctiocerae latum, and species
of Acroleuthis. To these may be added Inoceramus colonicus, I, ov&toidet,
Astarte californica, and Corbula filosa Stanton, all of which seem to lend
support from their occurrence in other sections.
In the Roaring River section above the lower Horsetown conglomerate
is a thick succession of sandy shales overlaid by shales almost without
sandy material. In the clear shales, about 1650 feet above the second
conglomerate and 1850 feet above the position of the Ono zone, is found