GEOLOGY — FORT READING. 27 



FORT READING. 



The geology of the vicinity of Fort Reading is not unlike that of the region lying imme- 

 diately south of it. The valley of Cow creek, in which it is situated, is hounded by ridges of 

 trap, of the brown and cellular variety, which is stereotyped in all this region. The trough 

 between these ridges is partially filled with a stratified deposit which is very soft, light gray 

 in color, and contains scattered lumps, of small size, of fine white pumice. 



There is little doubt that this deposit is tufaceous in character, and is composed of the lighter 

 and finer products of volcanic eruptions, rearranged by aqueous agency. It is probably of 

 recent date, and synchronous with somewhat similar beds which are found in various portions 

 of California, and are more recent than the tertiary cretaceous rocks. 



A few miles southwest of Fort Reading, at Arbuckle's diggings, a locality which I was not 

 able to visit, strata occur which are undoubtedly of cretaceous age. Ammonites, in consider- 

 able numbers, have been obtained there by Dr. Bates, of Shasta city, and a very handsome 

 species has been described by Dr. Trask, (Proc. Cal. Acad., vol. I, p. — ,) under the name of 

 Ammonites Batesii. 



To the occurrence of cretaceous rocks in this locality I shall have occasion to refer again in 

 a subsequent part of this report. 



Carboniferous limestone. — In sight from Fort Reading is a group of mountains, bearing east 

 of north, which, as we learn from Dr. Trask, are in a considerable degree composed of lime- 

 stone, which he has described in his Report on the Geology of the Coast Mountains, 1855, p. 50, 

 and which he regards as the equivalents of the upper carboniferous rocks of Iowa, &c. 



The limestones of these mountains, as described by Dr. Trask, have a great thickness and 

 are highly fossiliferous. While in San Francisco I had the pleasure of seeing through glass 

 the fossils procured by Dr. Trask from this locality, and although the number of species 

 collected is small, and they are probably all new, and cannot, therefore, be regarded as perfectly 

 conclusive criteria in deciding on the age of the containing rock, there seems to be little question 

 that they belong to some portion of the carboniferous group. Whether they are synchronous 

 with the upper coal strata or the sub-carboniferous limestone is a question which cannot be 

 definitely settled until a greater amount of material has been collected. 



These fossils consist of small spirifers, orthis, encrinal stems, and cyathophylloid corals. 

 The lithological characters of the rock are not unlike those of the sub-carboniferous limestone 

 of the Allegheny and Mississippi coal fields, but no value whatever can be attached to the 

 resemblance. 



It is very desirable that this deposit of limestone should be fully examined, and its fossils 

 carefully studied by some one who is sufficiently familiar with carboniferous palasontology to 

 determine accurately the relations which it sustains to the carboniferous rocks of the valley of 

 the Mississippi. With its great thickness it may very well be the representative of the entire 

 carboniferous series of the east; the open sea in which the carboniferous limestone was 

 deposited here continuing open sea, while the coal measures were being formed on the imme- 

 diate shores of the continent of that period. 



