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 

 palaeontology. While a careful study of the fossils of Chico creek will alone solve all the 

 problems which they suggest, it may be said that the evidence is still wanting upon which we 

 must discard one of the most authoritative axioms of palaeontology, 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 althougli much stress is laid by Dr. Trask (Proc. Cat. 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 Mactra 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 Baculites 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, 

 but 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 Tnoceramus in the Chico creek rock, and IB inclined to regard it as upper 

 cretaceous. 



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