GLACIAL AND INTERGLACIAL BEDS 305 



out into the valley of the present Lake Ontario. The lower 

 part of these deposits consists of very firm stratified clay 

 strengthened by sheets of clay ironstone ; but at the east- 

 ern end of Scarboro' Heights the clays have been greatly 

 crumpled and contorted, and even large blocks shifted and tilted, 

 by the pressure of the on-coming Wisconsin ice. As the delta 

 seems to have run about southeasterly it lay almost directly 

 athwart the course of the advancing- ice, which, after crossing 

 the later valley of the Laurentian river, had to climb over a 

 ridge at least 150 feet in height, and probably considerably 

 higher, before proceeding on its way diagonally across the 

 Ontario Valley. This obstruction, perhaps aided by climatic 

 variations, seems to have kept the ice more or less in check. 

 Meantime the lower end of the Ontario Valley must have been 

 blocked with ice so that the water once more rose assorting the 

 " rock flour" furnished by subglacial streams as gray stratified 

 clays without fossils overlying the uneven surface of bowlder 

 clay covering the series of ridges and valleys left by the inter- 

 glacial rivers. 



The halt at the Scarboro' delta was long and must have 

 included at least three great oscillations of retreat and advance 

 to account for the complex of tills separated by stratified mate- 

 rials now crowning the heights. The first sheet of till is shown 

 for about nine miles continuously at Scarboro' with the shape of 

 a slightly bent bow, touching the lake at each end and with a 

 sharp downward dip at the Dutch church. The latter is, how- 

 ever, less symmetrically placed than in a bow, being only three 

 miles from the west end and six from the east. 1 The hollow of 

 the Dutch church valley was filled with till containing compar- 

 tively few stones to a level 50 or 60 feet above the present 

 lake, then merging into gray stratified clay which rises to a 

 height of 165 feet, where it is covered with a few feet of much 

 later Iroquois beach gravel. Very similar clays rising to the 

 same height or a little higher are found at brickyards to 

 the north of Toronto. They burn to a gray brick and so are 



'See diagram, Jour. Geol., Vol. Ill, No. 6, 1895, p. 624. 



