GEOLOGICAL SOCIETY OF PENNSYLVANIA. 



203 



hundred feet deep, would rapidly enlarge the passage ; 

 and the outburst of the lake would sweep along with its 

 waters the debacle torn from its side, to distances pro- 

 portionate to the volume and force of the moving power. 

 In accordance with this hypothesis, such effects are now 

 visible in the accumulation of bouldered and transported 

 fragments, spread over the flats below the gorge, indi- 

 cating at the same time both the origin and the direction 

 and force of the escaping waters, and traceable uninter- 

 ruptedly for eight or nine miles into the Juniata. The 

 course of this detrital deposit we have shown in the map. 



On consideration, the view here taken of the pheno- 

 menon described in the foregoing pages, and the reason- 

 ing by which I have accounted in some measure for the 

 conversion of a deep lake into a deep and fertile valley, 

 would seem to be sufficiently conclusive. 



Should it be thought that we have dwelt too long on a 

 matter of local interest, let it not be overlooked that it 

 forms one link in the extended chain of research now 

 before us, a part of that immense field of investigation, 

 the frame work and physical structure of this vast 

 country, now inviting our individual and our united ex- 

 ertions. 



