GEOLOGY-CHICO CREEK TO FORT READING. 
25 
In either case the facts are of great interest, as indicating the presence of cretaceous rocks in a 
region where they had never been suspected to exist, or proving a new and important truth in 
paleontology. While a careful study of the fossils of Chico creek will alone solve all the 
problems which they suggest, it may he said that the evidence is still wanting upon which we 
must discard one of the most authoritative axioms of paleontology, and believe that the cepha¬ 
lopoda of the chalk continued to inhabit the Californian coast throughout all of the Eocene, and 
part of the Miocene tertiary periods. There are certainly no living species among those yet 
found in the Chico creek strata, and although much stress is laid by Dr. Trask ( Proc. Cal. Acad. 
Nat. Sciences, vol. I, ) on the recurrence there of living genera, it is a well known fact that a 
large part of the genera of the chalk are still represented in our seas. It is probable, too, 
that Mr. Conrad would not insist on his identification of Nucula divaricata and Mactrai albaria, 
as the specimens submitted to him were few and imperfect. It may also be ultimately proven 
that the argillaceous standstones of Astoria are not of Miocene age, for although having very 
much of a Miocene look, none of the species are found in the present seas, nor in other known 
Miocene strata. For the present, therefore, with unmistakable Baculiies and Ammonites* with 
no recent, and but two doubtfully Miocene species, the evidence is in favor of these strata being 
cretaceous rather than tertiary. 
CHICO CREEK TO FORT READING. 
Above Chico creek the Sacramento valley rapidly narrows ; that portion lying east of the river 
forming a nearly level plain, four to six miles wide, from which the foot hills of the Sierra rise 
abruptly. Between Antelope and Deer creeks I crossed over to the hills at a place where a stream 
coming down from the mountains, and at its point of entrance into the valley passes through a 
magnificent gate, of which the side walls are at least 500 feet in height. The rock in the 
vicinity is all a dark basaltic trap, which has been accumulated by successive overflows from 
some volcanic vent, probably not far distant. These lava floods, where exposed in sections, 
present a stratified appearance, some of the beds being imperfectly columnar. Though exhibit¬ 
ing very strikingly the phenomena of volcanic action, these trap hills are not of recent date, 
hut were probably formed synchronously with the upheaval of that part of the Sierra Nevada 
with which they are connected. 
The stream which flows through this opening in the hills in the rainy season is evidently of 
considerable size, and at the point of entrance into the valley was, at the time of my visit, 
(July 19,) still flowing, and contained large numbers of fish ; yet long before it reached the 
Sacramento its waters were absorbed by the arid plain traversed by its channel, and where we 
crossed its bed, near the river, it was perfectly dry, a gravelly trough containing not a drop 
of water. 
Our route from Antelope creek to Fort Reading lay across the hills which sweep around from 
the Sierra Nevada and, uniting with the foot hills of the coast mountains, form the northern 
boundary of the Sacramento valley. These hills we found composed exclusively of volcanic rock, 
generally a dark vesicular trap, which forms rough and ragged crests, divided by deep and 
narrow ravines, of which the sides are precipitous, or covered with angular blocks and frag¬ 
ments, among which we made our way with difficulty. In several places we passed over sheets 
of lava, which looked as though it had been but a few years since in a fluid state, the surface 
* Mr. F. B. Meek writes me that he also finds Inoceramus in the Chico creek rock, and is inclined to regard it as upper 
cretaceous. 
4 Y 
