13 



Such boulder pavements imply a long interval between 

 the two ice sheets in which the weather or running water 

 or more probably wave action could remove the clay and 

 allow the boulders to accumulate on the surface. The 

 second ice sheet must have come on gently at first until 

 the boulders were firmly sunk into the clay below, so as 

 to withstand the later grinding, polishing and striation. 



THE TORONTO FORMATION. 



After the recession of the first ice sheet there was a 

 long period of erosion and river action, in places removing 

 the boulder clay and cutting down into the shale. After- 

 wards a great lake filled the basin, laying down the beds 

 of clay, sand and gravel of the Toronto Formation upon 

 the eroded surface. 



The Toronto Formation is naturally divided into two 

 parts, the lower being the Don beds and the upper the 

 Scarboro beds. These two divisions differ greatly in their 

 fossils and were formed under different climatic conditions, 

 the Don beds including fossils proving a warmer climate 

 than the present and the Scarboro' beds others that indi- 

 cate a cooler climate. The two are never well displayed 

 in the same exposure, but the order of succession is cer- 

 tain, and there are places which show the Don beds under- 

 lying conformabjy the lowest portion of the Scarboro' beds. 

 Both were probably delta deposits, though of different 

 types ; but in the western part of Toronto there are inter- 

 glacial beds having the tumultuous cross bedding and irregu- 

 larity characteristic of strong currents and probably formed 

 by a large river. The exact position of these beds with 

 reference to the others is not quite certain, though they 

 belong to the same interglacial period. 



the; don beds. 



The best outcrop of the Don beds is to be found just 

 north of the sh ale jrit referred to before in the Don VaTTey~~ 

 brickyaTti, to THeeasT of Rosedale. The Pleistocene sec- 

 tion is 130 feet in thickness and includes not only the Don 

 beds, but an overlying series of unfossiliferous clays which 

 ^ were formed much later when the ice front was not far off. 



