LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

CRETACEOUS SEDIMENTARY DIVISIONS 49
Chico series and has not been found lower in the succession, Trppaeum
percQstatum (Gabb) represents a lower Gargasian horizon (middle Horsetown).
Polyplychitea troski belongs in the Hamlin-Broad zone, not found
at Arbuckle Diggings.. There is little evidence that any of the species of
this list were ever found at this locality, Its stratigraphical position is
below that of Locality 1&65 at Duncan Creek, and it should be older, and
therefore belongs in the Paskenta group, The beds exposed here can be
traced south toward Beegum Creek and ore among the oldest beds outcropping
north of the delta,
Identity of the Group.—On account of the faunal contrasts in the Paskenta
group north and south of the delta axis, some additional facts concerning
the essential identity of the strata are here offered. Both areas lie upon
the same side of the embayment within a geographical distance of 25 miles,
and with an intervening distance of less than 20 miles, There is little
difference in the two districts as to their environs, post or present. In
each, the sequence of faunas is nearly complete from early Valariginian to
middle Albian; each area includes, therefore, the entire sequence of the
Shasta series. The relation of the Paskenta group to the underlying
formations in the two districts differs only in the fact that north of the
delta it rests directly upon pre-Mesozoic crystalline rocks, whereas at the
south its lower beds rest in some places with seeming conformity upon the
Knoxville series. From these general facts it could be assumed that the
strata below the Horsetown group in the two areas must be contemporary,
and no other alternative seems to be open. However, in addition to
these facts, there are various diagnostic molluscan species common to both
areas, and, insofar as they occur, the faunal order is the same in both.
Other criteria have already been given in support of this view, which need
not be repeated here, for the reason that all other evidence seems unimportant
in view of the fact that the beds can easily be followed along their
strike from ono district to the other across the intervening delta area,
and, therefore, tbeir identity is hardly subject to doubt, whatever faunal
differences may be found.
DISTRIBUTION OP THE PASKENTA CROUP
General Statement.—The area! and geographical distribution of the
Paskenta group in California and Oregon far exceeds that of the Horsetown
group, since it occurs in many places in the Coast Ranges in both States
where no evidence of the latter group has been reported. Judging from
published reports this condition appears to extend to northern Washington,
to the mainland of British Columbia, and also to Alaska, In
most places along the Pacific Coast in which Lower Cretaceous deposits
have been recognized by their faunas, it is the lower, rather than the upper,
group that has been proved.
Yolla Bolly Bonn.—Only beds of the Paskenta group have been identi-