LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

CEBTACEOtTS BEDDJKNTABY DIVISIONS 85
replaced by races with which they could not compete. Probably not all
left fossil remains; some may have been shell-less. Evidences of battle
are numerous and indicate that shelled forms (e.g., Ancylaceras and crioceratids)
were vanquished, and their races disappeared soon after arrival.
A critical epoch in the order of cephalopod life in the Great Valley
trough was at tbe beginning of Horsetown time, as recorded in the faunas
of the early Cottonwood beds and in the succession that followed. These
successive faunas are dominated by types that are also dominant in nearly
the same order in the Lower Cretaceous of southwestern Asia, as also in
other regions.
To what event in the geological history of the Pacific basin, or of tho
world, could this abrupt change be attributed? Whatever the answer,
it is clear that important immigrations into this trough followed a quite
definite orogeny that seems to have affected in varying degrees the entire
Pacific Coast from California to Alaska, and perhaps far beyond.
Whether parallel facts could be recognized in Mexico and the Andean
countries cannot now be stated.
In some areas in Oregon, and apparently in California, Horsetown
deposits did not immediately follow those of Paskenta time. This fact
could be taken as evidence of local uplift and of withdrawal of the sea
from such areas. That the sea was withdrawn from certain areas of the
trough while still occupying others has already been shown. Far within
the outer limits of its expansion during Paskenta time are found thick
beds of conglomerate, marking roughly the strandlines of early Horsetown
time, particularly in the Cottonwood drainage areas. In other areas no
such conglomerates are found, and in some there are evidences of subsidence
and of overlap of Horsetown deposits upon pre-Cretaceou$ formations.
No lower Horsetown deposits have been reported from the Diablo
Range south of Quinto Creek, nor farther to the south, although they may
have been removed from many places or otherwise lost from view.
Although lower Horsetown deposits are indicated by fossils on Queen
Charlotte Islands, few have been reported from Alaskan areas, even where
beds of Paskenta age are known.
Without evidence to the contrary we may infer that the crustal disturbances
that ended Paskenta time and resulted in the conditions described
for the early Horsetown epoch in California were not local, although they
produced local effects not everywhere alike. Such differential results
have been described for some of the Andean countries and for Mexico
and the Rocky Mountains and seem to have affected other regions.
Burckhardt (1930) in describing these differential movements in Mexico,
which correspond to the uplift that closed the Paskenta epoch in California,
says in part:
"In marked eemtraM with this expansion of the sea there is shown in northern
Alcxica a regressive phase following Valanginian deposition."