LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

40 LOWER CRETACEOUS DEPOSITS INT CALIFORNIA AND OREGON
the Shasta series is set off from the underlying Knoxville and the overlying
Chico series by quite well marked unconformities. As has already
been shown (Anderson, 2933), its basal beds rest in some places discordantly
upon Knoxville beds, with thick basal conglomerates which
contain distinct evidences of diastrophism,, erosion, and transported material,
some of which is fossiliferous, derived from underlying Knoxville
and older formations. In other places the basal beds rest directly upon
pre-Knoxville (Franciscan, or older) rocks, as in the Yolla Bolly basin,
Morgan Valley, Russian River Valley, Mount Diablo, and the Diablo
Range. In a few exceptional places, as in the McCarthy Creek-Elder
Creek district, this unconformity is less evident, and the succession from
upper Knoxville to lower Cretaceous has been believed to be continuous.
Similar conditions are rarely found farther south, but for the most part
unconformity is readily proved. In many places the unconformity of the
two series is marked by bodies of conglomerate at the base of tbe Shasta
series, resting directly upon dark clay shales of the Knoxville series. In
some places they contain Upper Jurassic (Tithonian) fossils, These conditions
of unconformity have been found by N. L. Taliaferro 1 in southwest
Fresno County and in southern San Luis Obispo County, and are known
to extend as far south as the Santa Ynes River, Santa Barbara County.
The Shasta series is overlaid at the top by sediments of the Chico series,
having in many places distinctly basal, or near-basal, conglomerates which
contain evidences of unconformity. This unconformity was recognized by
both "White and Becker and has been observed in later field work by
others, including Taff (1935) and the writer. The geographical extent of
this unconformity is not yet known, although it has been found at many
places in northern California and in southwestern Oregon (Cottonwood
Creek, Cold fork, Elder Creek, Hornbrook, Jacksonville, and Riddle), and,
according to Martin (1926, p, 477-478), it seems to have been recognized
in Alaska (Yukon and Kuskokwim Valleys, Chitina Valley), although the
definite horizon of the overlaps are not always indicated.
The faunal changes in passing from upper Knoxville to Lower Cretaceous
beds are striking. Tbe Tithonian aspect of the former is seen in
the occurrence of many species of Cylindrateuihis, berriasellids of the
group of B. caliato (d'Orbigny), PhyUoteras, of the lineage of P. consanguineum,
and many characteristic forms of Awxlla, of the types found
in tbe upper Jurassic of Russia. In the Lower Cretaceous this assemblage
is roplaced by a distinctly different fauna, including other species of
BerriaseUa, Neccomites, Lytoceraa (group of L. saturnale nov.), Acrotenthis,
and Aucellae (gioup of A. cra&sicoilis, A. infiala, and A. lahuseni), and
by various forms of pelecypods and other classes of Mollusca.
As originally defined by Whitney (1869), the "Shasta Group"' (series)
> UopubUaied qo(n and fomil mHedlau.