12 



gravel, sand and clay, piled up at Scarboro' to a thickness 

 of nearly 400 feet. 



The earliest and most important interglacial series in- 

 cludes 185 feet of delta deposits; but the later ones are sel- 

 dom more than 30 or 40 feet in thickness, and may repre- 

 sent relatively short recessions of the ice. The retreat of 

 each ice sheet in the series was doubtless followed up by a 

 great glacial lake in which stratified deposits were formed. 

 That of the latest (Wisconsin) ice sheet was accompanied 

 by the waters of lake Iroquois, which lasted for thousands 

 of years and left behind the terrace and gravel bars and 

 shore cliffs which are such marked physiographic features 

 at Toronto. 



The earliest sheet of till consists of tough blue clay, 

 evidently made largely from the local shale, and containing 

 many angular slabs of its harder layers picked up close by. 

 With them occur some well rounded polished and striated 

 boulders of blue Trenton limestone, smaller boulders of 

 black Utica shale, and many large or small boulders of 

 granite, gneiss, greenstone or schist from the Archaean. No 

 smoothed or striated surface has been found beneath the 

 lowest boulder clay, which seems to pass down into the dis- 

 turbed Lorraine shale; but the direction of the ice motion 

 is indicated by the boulders of Utica and Trenton rocks, 

 which are found in place in eastern Ontario. 



The lowest boulder clay is usually not more than three 

 or four feet thick, and in a few places it is wanting, having 

 been swept away by interglacial rivers. Its best exposure 

 is in a shore cliff near the west end of King street in Park- 

 dale, where it rises four or five feet above the lake and is 

 capped for 800 feet by a well-laid boulder pavement. Above 

 the pavement there are 25 or 30 feet of less solid till formed 

 by the next ice advance, with no interglacial beds inter- 

 vening. 



The flat upper surfaces of the stones in the boulder 

 pavement are usually well and uniformly striated, the direc- 

 tion ranging from 290° to 315 with an average of 300 . 

 The strise run 30 north of west instead of south of west, as 

 might have been expected. The glacial lobe which had fol- 

 lowed the depression of lake Ontario from the east began 

 to spread out towards its west end. A similar boulder 

 pavement occurs in a shore cliff near Port Credit ten miles 

 to the west. 



