LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

46 LOWER CRETACEOUS DEPOSITS INT CALIFORNIA AND OREGON
a considerable list of plants, nine of which were specifically named, with
three others named only generically. These plants were determined by
Knowlton, whose assignment could be interpreted to mean tbe uppermost
beds of the Knoxville series, as here understood. The horizon is that of
"Zone K," of an earlier contribution (Anderson, 1933, p. 1252). The
foregoing list contains the most characteristic molluscon species found
here in the lower part of the group. The upper portion of the group in
this district is composed almost wholly of slightly indurated clay shales,
in which there are occasional lenticular, but thin beds of limestone, and
more rarely thin beds of sandstones. In the lower part of these shales
on McCarthy Creek, not far east of the Burt ranch house, are found
tfeocomite* jcnkinri nov., Thurmannia paekentae nov., Subaslicrta sp.,
AuceUa nuciformis Pavlow, A. terebraiuloidea Lahusen, and various plant
remains. About 1200 feet higher in the section on McCarthy Creek were
obtained a fragment of Lytoccras satumale and AuceUa piriformis, and with
them a large leaf of a cycad species and other plant remains. In the dark
shales not far above this horizon were found a small species of Lytaczraa
ef. L. traski nov. and a small species of AuceUa. Farther south the upper
shales of this group have not yielded determinable fossils. Such shales
appear in the same stratigraphic position in the section as far south as
the Berryessa Valley, but no fossils have been found in them. In lithological
character these shales do not differ from those of the Horsetown
group nor from shales in the Knoxville scries, as found farther west.
The line of division between the Paskenta group and the overlying
Horsetown beds in this district is not marked by any lithological change,
and its position is often a matter of approximation or of doubt.
Cctlonwood District.—In tbe northern part of the Cottonwood districtthat
is, in the triangular area north of the Middle fork and west of Ono—
there is a thick sequence of sandstones, sandy shales, and clear dusky
shales, and at their base some bouldery conglomerates, The entire
sequence lies below the fossil-bearing beds at Ono and beneath the conglomerates
here regarded as forming the basal beds of tho Horsetown
group. Stratigraphieally these shales and sandstones occupy the position
of the Paskenta group as found in its type district. Westward from Ono
this group becomes progressively thicker by the successive emergence of
lower beds along its contact with the basement rocks. North of Roaring
River the group varies in thickness from less than 1000 feet near Ono to
nearly 4000 feet on the upper Roaring River. The Lower Cretaceous age
of these beds is unquestionable, and, although faunally unlike those of the
Paskenta group on McCarthy Creek, and northward, lacking its Aucellan
fauna, it must be regarded as forming a facies of this group and as being
of contemporary deposition. In its lithological order there is much similarity
in the two districts, in that the lower half of the group is prevailingly