in some of our Post Tertiary Deposits. 45 



of their occurrence. In his annual report of 1838 he remarks 

 that Uhiones are said to have been found in the ridge. Should 

 the shells of this deposit prove to be of fresh water origin, and 

 since no marine shells have been found in it, we might be induced 

 to beheve that Lake Ontario once stood far above its present 

 level, and that a barrier which kept it at that level has since been 

 removed ; but on the contrary, as there is no actual proof that 

 such a barrier did exist, we have reason to conjecture that it was 

 formed while the sea stood at that level. Allowing the water by 

 which the Lake Ridge was thrown up to have been 175 feet 

 over the present level of Lake Ontario, we should have about 410 

 feet as its elevation above the present sea level ; this corresponds 

 exactly with that of the littoral deposit in Nepean on the Ottawa, 

 in which Sir Wm. Logan has found marine shells, and it would 

 not be surprising if future researches prove them to be contem- 

 poraneous — perhaps also with the terrace on the back of Montreal 

 Mountain which is 50 or 60 feet higher, — for littoral deposits at 

 considerable distances apart may be of the same age though at 

 different elevations, as these differences may be due to an unequal 

 amount of upheaval or to a difference in the heights to which the 

 tides rose. 



One of the numerous terraces which run along the north side 

 of the lake will no doubt be found to mark an elevation corres- 

 ponding to that of the " Lake Ridge " on the south ; probably 

 the "Pine Ridge" which is so well marked is the one. The 

 late Mr. Roy, who long ago levelled the terraces behind Toronto, 

 gave 108, 208, 280, 308, 344, 420, 680 and 762 feet as the eleva- 

 tions there of ancient beaches above Lake Ontario. 



Dr. Dawson the other day showed me two specimens of a 3fe- 

 lania and one of Unio ellipsis from a sandy deposit not far from 

 Toronto.* They are described as having been found immediately 

 above the Silurian roek in the drift about five miles from the Asy- 

 lum. Both the Melanias are filled with sand but on the back 

 of the Unio there is a thin layer of clay which again is impre- 

 gnated with sand. The deposit from which these shells are de- 

 rived may be of the same age as the ridge on the other side of 

 the lake. 



Professor Chapman informs me that he has collected specimens 

 of a Planorhis in sand and gravel about 46 feet above the lake in 

 the neighbourhood of Belleville. 



* Collected by B. Workman, Esq., M.D. 



