Geology of the Lakes and the Valley of the Mississippi. 211 



in river alluvions ; and it is nearly certain that we owe their extinc- 

 tion to no catastrophe whatever.* 



Remark by the Editor. — It will be perceived that the subsequent 

 observations of Judge Gibson, have reference to a letter addressed 

 to him by the Editor; the object of that letter will be apparent on 

 reading the subjoined answer. 



Carlisle, Penn. Aug. 19, 1835. 



To Prof. Silliman. — Dear Sir — I feel strong in my position 

 that the limestone described in my article, is consubstantial with the 

 lias. This rock is described by Mr. Bakewell and Mr. De la Beche, 

 if I mistake not, (for I have not the books at hand,) as a collection 

 of limestone and shale, in layers resting on the new red sandstone, 

 and constituting the undermost member of the oolitic group. That 

 the rock at the cataract answers this description, except that it is the 

 terminating member of the ascending series, will not, I think, be dis- 

 puted. About the character of the red sandstone, there can be no 

 more doubt than about the character of the coal measures, on which 

 it visibly rests, and whose outcrop appears at the foot of the Allegha- 

 ny mountain, distant forty or fifty miles. The sandstone, with the 

 limestone it supports, exhibits a gentle but perceptible dip, whose 

 direction conforms to the flank of the mountain. Its external ap- 

 pearance, as well as its geological character and accompaniments, is 

 precisely that of the same rock in Europe. 



Deposited on this red sandstone, we find an aggregation of lime- 

 stone and shale, containing mollusca common to the lias, and disposed 

 in layers, of which nothing can be more distinctively characteristic, 

 than the lateral edges over which the water gambols, at the falls, with 

 such wild and fantastic agility, before it makes its final leap. I pre- 

 sume this rock will not be considered sui generis, or an anomaly, so to 

 speak, in the geological kingdom ; and if not, to what inferior group is 

 it to be referred ? Not to the carboniferous ; for the interposition of the 

 red sandstone, is a bar to that. Not to the red sandstone itself; for 

 that has no limestone but the zechstein, from which the limestone at 

 the falls palpably differs. That its mineralogical character differs 

 from the specimens of the English Has I have seen, I am free to ad- 

 rait ; but how entirely incompetent a comparison of cabinet speci- 



* Doubtless the author is aware that mastodons have been found in the tertiary 

 in Europe, as well as in the diluvium, and we must wait to see whether the fact 

 ■will prove to be the same in this country. — Ed. 



