02 AMERICAN JOURNAL 



or only represented by fine lines of growth." I might add, that 

 these variations occur entirely without reference to the two 

 geological horizons. 



Nucula truncata. Mr. Conrad, starting with the theory that 

 I have united two formations, when he finds a species quoted 

 as occurring in both deposits, coolly disposes of it by saying: 

 " Two species are evidently confounded under this name.'" 

 How. "evidently,' 1 ' 1 I cannot understand. Certainly, I, with a 

 hundred specimens before me, should have better means of 

 knowing, than my critic, who has never seen so much as a 

 single specimen, and only one drawing. 



Leda protexta. The remarks made on the preceding species 

 will apply with equal propriety to this. There is but one 

 species in California included under this name, though I was 

 not quite sure of the correctness of my reference. 



"The remarkable and very characteristic fossil, Radiolites 

 gregaria (Tamiosoma gregaria, Con., Glim.), abundant in Cali- 

 fornia, has been omitted by Mr. (fabb in his report," because 

 neither Mr. Gabb nor any other member of the Geological 

 Survey ever found even a fragment of the species among the 

 tons of fossils collected by those gentlemen. It is even doubt- 

 ful whether the species may not be extra-limited, and whether 

 Mr. Conrad may not have been misinformed regarding its 

 locality. 



In conclusion, permit me to repeat, that I regret exceed- 

 ingly having been forced into this discussion, though I trust 

 that I have answered the objections of my critic in such a 

 manner as to convince him that he was mistaken in his views 

 in regard to the geological age of my Division B' of the Cali- 

 fornia Cretaceous Rocks. 



Sun Francisco, Cal., Nov. 14, 1865. 



