Geology of the Lakes and the VaUeij-of the Miss-issippi. 21 1 



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

 tion to no catastrophe whatever,* 



\ 



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

 observations of Judcre 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. 



CaiTis!e, Penn. Aug. 19, 1S35 



To Prof. Silliman. — D 



•1 feel stronii in 



my position 



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



lias. 



Mr 



(f 



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



and 



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, tliere 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 accom]5animents, is 

 precisely that of the same rock in Europe. 



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

 stone and shale, containing moUusca 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 fant'Lstic 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 lias I have seen, I am free to ad- 

 mit ; but how entirely mcompetent a comparison of cabmet speci- 



* Doubtless the author is aware that mastodons have been found ia the tertia^ 



5^ -rr .1 j-1 ',^r^ anri tt-p most wait to see whelaer ine tact 



la Europe, as well as in the diluvium, and we mubi uai 



^ill prorc to be the same in this country.— Krf. 



