THE GEEEN ElVER COAL BASIN. 463 



physical changes had taken place here, or were taking place, at the time they 

 were deposited, since these shells are all such forms as we could only ex- 

 pect to find mingled together in an estuary deposit; while those from the 

 whitish sandstones beneath as clearly point to a marine origin. This strongly 

 marked change in the fossils, observed in passing from the lower to the upper 

 of these formations, and the close similarity of those from the latter to for- 

 eign lower Tertiary species and living forms, and the entire absence, so far 

 as known, of any characteristic Cretaceous types in these upper beds, are the 

 grounds on which Mr. Henry Engelmann and the writer referred them to the 

 Tertiary, in 1860. 



One species, in the collections from the older marine sandstone under 

 investigation, agrees so closely with Corhula pyriformis, from the estuary beds 

 of Bear River, that I am strongly inclined to believe it belongs to the same 

 s^jecies. The specimens in the sandstone are all merely casts, but they cer- 

 tainly agree in size and form with those from the brackish-water beds. The 

 oyster. No. 1 of the above list, also seems to be the same as No 1 of the list 

 of Chalk Creek species, two miles above Coalville, and No. 13, from Coal- 

 ville ; though I am not sure that the specimens from Bear River of this oys- 

 ter were found directly associated with the estuary fossils, especially as the 

 marine sandstones also occur there. 



On comparing these collections with the fossils described in the Califor- 

 nia Reports, I observe that a shell, figured by Mr. Gabb, under the name 

 Corhula Tiornii^ from the very latest beds, referred by Professor Whitney to 

 the Upper Cretaceous in California, is very similar to the Utah species, Cor- 

 hula pyriformis. Indeed, I find nothing either in the figure, or in the de- 

 scription, of the California shell to distinguish it from the Utah species, or 

 rather from a variety of the latter, with more regular and stronger marked 

 lines and furrows, to which I had applied the name C. concentrica, but which 

 I have since found to be only a variety of C. pyriformis. The oyster men- 

 tioned above as being apparently common to the estuary and marine beds 

 seems to be also closely allied to O. Idriamsis, described by Mr. Gabb, from 

 the highest of the California rocks referred to the Cretaceous. Oysters, how- 

 ever, often so nearly resemble each other, from rocks of different ages, that 

 not much stress can be laid upon this apparent identity. 



