Geology of the Lakes and the Valley of the Mississippi. 213 



You inform me that Dr. Hildreth, in his account of the coal for- 

 mation, has described the lias. I had flattered myself with an ex- 

 pectation of being the first to perceive and point out its true char- 

 acter ; and I shall still contend for that honor, notwithstanding Dr. 

 Hildreth's mention of this rock, as my letter to the Geological So- 

 ciety of Pennsylvania, already in print, contains a description of it, 

 with an assertion that it is identical with the foreign lias. 



In regard to the diluvium, my remarks were not predicated of the 

 diluvium in Europe, but of facts which actually exist here, and they 

 were made in order to corroborate Prof. Rogers' confutation of the no- 

 tion of Mr. Deholme, that the mastodons of America were extirpated 

 by the flood which deposited the diluvium in the valley of the Missis- 

 sippi and Ohio. It was unnecessary to speak of the period to which 

 these animals may be thought to belong, or their place in the ter- 

 tiary elsewhere. Perhaps small fragments of their bones may have 

 been found in the strip of tertiary resting on the primitive rocks in 

 Jersey near Sandy Hook. What relation the diluvium bears to it 

 here, it is yet impossible to say ; but my own opinion is that our 

 diluvium is not contemporary with that of Europe. The lias seems 

 to be the point of divergence at which the unity of deposition 

 ceased, and the appearance of diluvium became as accidental and 

 local as the ejection of the intrusive rocks. I have not room to state 

 my reasons for this; but I will add, that in the valley of the Mis- 

 sissippi, the bones of the vertebrated animals there, lie, without ex- 

 ception, above the diluvium. 



As you inform me that the existence of the lias has been posi- 

 tively denied — a fact of which I was not aware when I wrote ray 

 article— I should prefer to have appended to it, at least, the first 

 paragraph of this letter accompanied, however, by any remarks, 

 critical or explanatory, which you may deem proper.* 



* We have given the whole of Judge Gibson's letter that was necessary to sus- 

 tain his opinion. — Ed. 



