6 H. Doc. 129. 



fossils collected in California by Dr. Heermann, consisting of decidedly 

 Miocene forms ; a Mercenaria, (M. perlaminosa,} Con. , scarcely differing 

 from a species of Cumberland county, N. J., (M. Ducatelii, Con.,) a 

 Cemoria, Pandora and Cardita of extinct species, closely analogous to 

 Miocene forms. I am inclined, also, to refer to this period a very 

 different group from Ocoya creek, the forms of which you sketched in 

 California, as the specimens were too friable to be preserved. I do 

 not recognize any recent species among them, nor any contained in 

 an Eocene deposit. 



The rock at San Diego is replete with shells, generally of a small 

 size, and appears to have a certain palasontological relation to those of 

 Monterey, Carmello, and those in boulder specimens of Oregon, col- 

 lected by Townsend and Dana, which I have referred to the Miocene 

 period. Two species of San Diego, if not identical, approach Oregon 

 shells ; Nucula decisa is similar to N. divaricata, and both, in their 

 markings, resemble N. cobboldii of the English Miocene. Mactra 

 Diegoana is nearly related to the Oregon M. alboria. 



The Eocene period is unequivocally represented by the beautifully 

 perfect shells from the Canada de las Uvas, which, though not found 

 in situ, are evidently derived from strata occurring on the Pacific 

 slope of the Sierra Nevada. This is very remarkable, inasmuch as 

 three species correspond with forms of Claiborne, Alabama, and seem 

 to indicate a connexion of the Atlantic and Pacific oceans during the 

 Eocene period. The vast distance between the two localities will 

 account for the general distinction of species, and it was, indeed, an 

 unexpected result to find any identical. If I had imagined any east- 

 ern species to occur in California, it would have been the very one 

 which does occur, and, apparently, in abundance, that "finger-post" 

 of the Eocene, Cardita planicosta, a fossil of the Paris basin, and also 

 abundant in Maryland, Virginia, and Alabama. This species origi- 

 nated and perished in the Eocene period, and is so widely distributed 

 that it may be regarded as the most characteristic fossil of its era. As 

 the boulder from which these shells were derived was quite small, and 

 yet furnished thirteen species, when it shall be investigated in situ, 

 doubtless a great many other forms will be obtained, and very likely 

 some with which we are already familiar in eastern localities. Al- 

 though the rock is a very hard sandstone, the shells may be exposed 

 in great perfection by careful management, and we look forward with 

 great interest to their further development, and to the discovery of 

 the rock in situ. 



Respectfully, yours, &c., 



T. A. CONRAD. 



WM. P. BLAKE, Geologist of the United States 



Pacific Eailroad Survey in California. 



