and the Geology of the Surrounding Country. 125 



Unio, Cyclas, Limnea, Planorbis, Valvata, and Melania ; the 

 same both in genera and species as those now inhabiting the 

 river and lakes. The occurrence of these shells, in this situ- 

 ation, about twentyfive feet higher than the top of the fall, 

 proves the existence of a river or lake at an elevation suffi- 

 cient to allow of such a deposition, for this accumulation of 

 shells and gravel bears all the evidence of a fluviatile deposit. 

 During the past season, in company with my friend, Mr. 

 Lyell, I re-examined this region, and upon the east side of the 

 river, in a terrace about the same elevation as Goat Island, we 

 discovered the Cyclas, Valvata, ifec. which had been thrown 

 from an excavation made several years since. At the same 

 place, a tooth and some bones of the Mastodon were discover- 

 ed eleven feet beneath the fluviatile deposit. Farther north- 

 ward, and more than half a mile north of Goat Island, in 

 another excavation, we discovered similar shells. We also 

 noticed the continuation of this terrace, or one about the same 

 elevation, as far north as the whirlpool. We did not search 

 for shells in it at this place ; but from its character and posi- 

 tion there can be little doubt but it is a continuation of the 

 same deposit, and probably will be found to contain the same 

 shells. Now in order to raise the water of the river to suffi- 

 cient height to make this deposit, it w^ould require a barrier 

 for the water at some distance north of the whirlpool. On 

 the other side of the river a similar terrace exists, but this I 

 have not particularly examined.* Now these banks or terra- 

 ces on either side of the river, and that of Goat Island, are 

 clearly not deposits made in this form, but the remains of a 

 once much more extensive one. During the time of its de- 

 position the river occupied this valley, having its barrier far 

 towards Lewiston. In the bed of this expanded river or lake, 

 much as it now is above the rapids, this deposit was made, 

 covering the whole extent ; but from the wearing back of the 

 fall it has been carried off, the margin only being left on 

 either side, and a small portion of the central part forming 

 Goat Island. The following diagram will exhibit the posi- 



• iMr. Hayes speaks of the terraces on both sides of the river, as containing 

 fresh water deposits. Amer. Journal of Science, Vol. XXXV, No. I. 



