3^ 



THE IROQUOIS B^ACH DEPOSITS. 



After the last ice age, when the retreat was well under 

 way, the basin of lake Ontario was freed from ice while 

 its outlet at the Thousand islands was still blocked. The 

 water escaped by the Rome outlet, in the State of New York, 

 to the Hudson, and a lake which has been named Iroquois 

 by Dr. Spencer, occupied the basin at a much higher level 

 than that of lake Ontario. The southern slope of Toronto 

 is largely covered with its deposits, the old shore cliff runs 

 east and west through the city, and at each end a great 

 gravel bar extends across the present river valley. 



The Iroquois beach is deformed and rises from 176 feet 

 above lake Ontario at the Humber gravel bar toward the 

 west to 196 feet at the York gravel bar crossing the mouth 

 of the ancient Don bay, and to 200 feet at Scarboro heights. 

 The shore cliff within the city north of Davenport road 

 averages about 75 feet in height, but at Scarboro reaches 

 in places 170 feet. At the highest point of the Scarboro 

 cliff it is completely cut off by the shore of lake Ontario 

 for half a mile, the only known point at which the waves 

 of Ontario have encroached on the ancient shore line. 



Lake Iroquois began its work at least 70 feet below 

 its latest well marked beach, but none of the earlier stages 

 is shown at Toronto. Beside the cutting of a terrace in the 

 Pleistocene deposits with the cliff at its rear the lake did 

 much work in distributing materials, filling in former de- 

 pressions in the terrace, and building the two great gravel 

 bars in west and east Toronto respectively. Each of these 

 bars began on the east side of its bay and grew westwards, 

 crowding the river out of its earlier channel and forcing 

 it to the western shore of the bay. 



The bar in west Toronto crossing the Humber bay ex- 

 tends west as a uniform and rather narrow ridge of gravel 

 and sand rising 20 feet above the slope to the south, while 

 the York (or east Toronto) bar enclosing the Don bay is 

 more spread out and contained lagoons. It had much the 

 size and shape of the present Toronto island. 



Both of these ancient bars are being rapidly destroyed, 

 the sand and gravel being used for building purposes in 

 Toronto. 



The Iroquois deposits are sometimes 100 feet thick and 

 include coarse materials in the gravel bars, sand of varying 



