Geol.— Vol,. II.] ANDERSON— CRETACEOUS DEPOSITS. 35 



mistaken, or at best are not characteristic. One or two 

 species of Turrttella are found in the Lower Chico, and 

 four in the Upper, only one of which is common to both. 



Among bivalves a greater number of forms is found, 

 continuing from the earlier to the later deposits; but this is 

 perhaps to be expected, partly from their more simple habits, 

 and partly from their greater numbers. But with these also 

 a critical examination will result in lessening their apparent 

 importance. Not more than twenty species are shown to 

 have survived from the earlier to the later Chico, and among 

 them are Chione varians, Uomomya concentrica, Exogyra 

 parasitica, Afeekia sella, and perhaps Inoceramus whitneyi, 

 none of which are of very decisive character. Of the 

 others, Pecttinculus veatchi, CucuUcea triincata, and T^i- 

 gonia evansana, while they are more distinctive forms, have 

 each near allies in the Cretaceous of the West Coast, among 

 which there has not yet been a close discrimination. Tti- 

 gonia dawsoni, from the Queen Charlotte Islands, is related 

 to Trioronia evansana of the Comox beds. There are at 

 least two varieties of Pectunciilus veatchi, besides a new and 

 nearly related species, while Cncullcea truncata from the 

 Chico resembles superficially a Trigonarca from the Queen 

 Charlotte Islands. One needs to be reassured by careful 

 comparisons before yielding to first impressions. Nuciila 

 truncata, if not some of the others, has caused a similar 

 confusion elsewhere by crossing a well established break 

 from the Chico to the Tejon, and even into the Miocene, 

 and ought not to be regarded seriously here. 



But the distinction between Upper and Lower Chico 

 does not appear to need this sort of defense. It could be 

 properly made even if a much larger number of species 

 was found to have crossed the interval. It may be true 

 that a larger number will be found when the localities are 

 more carefully searched; but even so, future explorations 

 will probably also increase proportionally the number that 

 have not crossed the line ; so that it is safe to say the ratio 

 of species that have survived from the earlier epoch will 

 not be materially increased. 



