T94 Q&OLOGy. 



LETTER XLV. 



Western Region, August, 1820. 

 My Dear Sib., 



In a late letter I attempted to show that the 

 1 * ». as continually gaining on the lakes, by the 

 i acy of calcareous depositions, and I think that 

 I ,nted out a region of schistic formation, lying 

 5 itfa of the great lime stone ledge of the west. 

 That this caicareous formation dips to the south, 

 I have no doubt, but whether it underlays the 

 schistic, I have not been able to ascertain. This 

 southern depression of the calcareous ledge below 

 tl crumbling slate, would necessarily create ba- 

 sins for the springs and rains of the country, and 

 which by wearing away that fragile substance, 

 would in time expand into lakes. This is evident- 

 ly the case with the Cayuga lake, which is con- 

 tnKuliv enlarging its borders; and the fall of old 

 ledges from the precipices demonstrates that the 

 present order of things has not been of very re- 

 mot? antiquity. 



The shores of Lake Erie are sustained by strata 

 of schistic which are continually giving way be- 

 fore the violence of the waves, and the whole lake 

 Is supposed to be in a state of continual expansion. 



