46 On the occurrence of Freshwater Shells 



Altliough some of the lower terraces behind Toronto might 

 have been formed by the lake when at a greater elevation, the 

 higher ones were doubtless formed during the period of the glacial 

 drift. 



I will mention a circumstance which may be one reason for 

 inferring that Lake Ontario was filled with fresh water at the time 

 when the sea stood at one of the best marked zones of the Post 

 Pliocene formation to the eastward. It is well known that the 

 very common little bivalve Tellina groenlandica delights in salt 

 water which is largely mixed with fresh and is most abundant in 

 friths or bays where rivers enter the sea. In descending the St. 

 Lawrence from Quebec, it is the first marine shell one meets with 

 and is extremely abundant when the upper limit of other marine 

 species is reached. When the salt water extended up the valley 

 of the St. Lawrence to some point between Montreal and Kings- 

 ton, we should naturally expect the same state of things to have 

 existed. Now, in the drift deposits at Prescott, at about 250 feet 

 above the sea, Tellina groenlandica is very abundant and T did 

 Dot observe any other species ; from this fact, and considering the 

 situation of the locality, it appears evident that the estuary was 

 here diluted with fresh water when the sea stood at this level, but 

 the argument is open to many objections. 



Niagara Falls. 



In 1859 an opportunity was afforded me of examining the an- 

 cient bed of the Niasfara River near the Falls. Between the 

 Clifton House and the toll-gate below, a deposit of gravel and 

 sand, rich in fluviatile shells, occurs between the ancient bank of 

 the river, and the cliff overhanging the present gorge. At a spot 

 on the road-side where a quantity of the sand and gravel had 

 been excavated, I collected the following species : — 



1. Planorhis bicarinatus. 9. Amnicola porata. 



2. Physa heterostropha. 10. Unio gibbosus. 



3. Limncea caperata, ll. ** complanatus, 



4. " stagnalis. 12. '* ellipsis. 



5. Melania JViagarensis. 13. '* rectus. 



6. " conica. 14. Margaritana marginata. 

 1. " acuta. 15. Cyclas similis. 



8. Paludina decisa, 16. Psidium dubium ? 



A portion of a land snail, probably Helix albolabris was also 



