I900-I.] Physical Geology of Central Ontario. 165 



question of the origin of the basin of Lake Ontario. Although over 

 large areas the topography of the rock floor beneath the Pleistocene 

 deposits cannot be ascertained, there are also large areas in which there 

 is no difficulty in determining its essential features, often even to minute 

 details. Since the interpretation of the features of this rock topography 

 depends upon its relation to the overlying Pleistocene debris, it has been 

 thought best to first describe in outline, these latest deposits. 



Pleistocene Deposits.— YWx\d.Q (77), Coleman {'94, '95, '97, '98, '99, 

 1900), and others, have described Pleistocene deposits occurring in the 

 vicinity of Toronto, notably at Scarboro' Heights, describing three sheets 

 of glacial till. The two upper sheets overlie thick deposits of stratified 

 and finely laminated clays and stratified fossiliferous sands and gravels. 

 (Plate I.) One hundred miles east of Toronto, just north of 

 Trenton, occur series of deposits in which is cut a sea-cliff attributed to 

 Lake Iroquois. The crest of the Iroquois sea-cliff is 718 feet (bar.), and 

 the rock surface just east of this, along the Trent River is about seventy- 

 eight feet above Lake Ontario.* The total thickness is thus 640 feet. 

 These deposits show three till sheets alternating with two series of strati- 

 fied beds, chiefly sands and gravels. The precise thickness of each of the 

 five series of beds has not been ascertained as yet, but the till beds 

 certainly, and the stratified beds probably, are much thicker than the 

 similar beds at Toronto. 



Between this locality and Toronto, in each of four other transverse 

 sections northward from Lake Ontario, the three till sheets have been 

 encountered by the writer. In a trip, on foot, along the lake shore from 

 Presqu' Isle to Burlington beach, the two lower of these three till sheets 

 have been traced for a long distance. East of Port Hope, between Bow- 

 manville and Whitby, and west of Toronto, a till sheet rests in many 

 places directly upon the rock surface. Sometimes only the upper 

 portion of this sheet is visible, and occasionally it passes wholly below 

 the lake level. Provisionally this lowest sheet may be considered as 

 the equivalent of the lowest till sheet at Toronto and at Trenton. 



From Port Hope westward a second till sheet, with varying thick- 

 ness, resting upon stratified deposits, both sands and laminated clays, 

 and once (near Oshawa) upon the lower till sheet, can be followed along 

 the lake shore almost continuously to Scarboro'. At Scarboro' there is 

 a nearly continuous section about nine miles in length. Between Port 

 Hope and Trenton the edge of this sheet lies from one to four miles 



*There is a continuous exposure of rock surface along- the Trent, transverse to the ridge, and in a 

 number of localities to the eastward the general topography of the rock surface can be well established. 



