LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

CRETACEOUS SEDIMENTARY DIVISIONS 83
Parahoplitidae are almost, if not entirely identical. Among the aneyloceratids
may be mentioned Tropaeum and Au&iraHceras. Such analogous
species are found also in the early Albian of the California embayments.
These facts can be understood only on tbe assumption of suitable routes
of exchange across the Pacific basin during early Cretaceous time, possibly
beginning in the earliest epochs of the period, but at all events
existing during later times.
Such routes of travel should lie far to the south rather than to the north.
The absence of most, if not all, of the older Horsetown ammonoids from
Alaskan and Japanese Cretaceous deposits seems to harmonize with this
view, although such evidence is somewhat negative and not conclusive.
Many known facts concerning the Pacific basin and the terrestrial and
marine faunas, past and present, upon its borders support tbe hypothesis
of a land bridge across the south Pacific during late Mesozoic times. To
what extent Burckbardt's (1900b) evidences of an ancient Pacific continent
would support this hypothesis is not known. Gregory (1922) and
others have supposed that direct communication between Atlantic and
Pacific waters existed in the Panama region during later Cretaceous time,
but convincing evidence of this has not been given. There is little in
common, however, between the early Cretaceous faunas of the northern
Andes and Mexico on the one hand, which are typically Mediterranean,
and the contemporary California faunas, which are Indo-Pacific in character.
This fact seems to be true also for the later Cretaceous faunas
in these regions.
The existence of a trans-Pacific land bridge in Mesozoic time has been
suggested by various writers in the past, but the subject has been more
recently revived and enriched by much new evidence that has been summarised
by Gregory (1930) and others, supporting the assumption. The
topic has also been recently discussed by Schuchert (1930) who seems to
have been not entirely satisfied with the evidence offered by von Huene.
The possibility of such a bridge, or bridges, has been given support by
data supplied by Chubb (1934) who has studied the distribution and
character of the continental rocks in the general areas of tho South Pacific
and given his interpretation of the same.
We may be justified in accepting the evidence and deductions of these
writers and in believing that during early Cretaceous time land connections
between southwestern Asia and western South America had existed,
in effect at least, dividing the area of the present Pacific into two more or
less equal parts. This bridge is thought to have extended across the
Pacific, mainly south of the Equator, reaching South America in the latitudes
of northern Chile and southern Peru. For the migration of some
forms of Mollusca, including cephalopoda, complete land connection may
not have been essential, if we assume the existence of ocean currents