170 A. p. COLEMAN LAKE IROQUOIS AT TORONTO 



worked out.* A glance at the diagram Avill show that the curve rai)id]y 

 approaches a horizontal line as it advances southwest, and thathorizon- 

 tality would be reached much above sealevel. On the other hand, it is clear 

 that the northeast [)rojection of the curve would run far above the 600-foot 

 beach at Montreal, or any elevation at which marine shells have been 

 found, along the rivers flowing into Hudson bay. It can not be assumed, 

 of course, that the curve of elevation would continue indefinitely toward 

 north 17 degrees east. There must be somewhere a gentle anticline, 

 beyond which there is a downward slope, unfortunately not recorded in 

 the wide valleys of the Saint Lawrence and Ottawa. 



The researches of Messrs Gilbert and Taylor seem to prove that after 

 the Iroquois lake was drained there was a short time during which the 

 gulf of Saint Lawrence extended into the Ontario basin, f and it may be 

 that the whole of the marine beaches of eastern Canada are post-Glacial 

 in age, and therefore later than the Iroquois beach. 



Interglacial Water-levels 



Thus far we have followed in brief outline the record of changes of 

 water-level as disclosed in old beaches, and a most wonderful and com- 

 plicated history, even yet only iniperfectl}^ understood, has been unrolled 

 before us by Gilbert, Spencer, Taylor, and others. It must not be for- 

 gotten, however, that this tangle of beaches and deserted waterways 

 represents only the latest series of episodes in the history of the Great 

 lakes, the results of the removal of the last ice-sheet and of the later 

 changes of level of eastern America. We may imagine that the slow 

 advance of the great ice-sheet produced a similar series of lakes, but in 

 ascending instead of descending order, beginning with a greater lake 

 Ontario far earlier than the Iroquois lake, proceeding to a lake Algonkin, 

 a lake Warren, and a lake Agassiz. Unfortunately this must all be left 

 to the imagination, since no record of the first ice advance, in so far as it 

 affected water-levels in the Great Lakes region, has been discovered up to 

 the present. The same may be said of the earlier inter-Glacial period or 

 periods. It is only when we come to the later inter-Glacial times, which 

 have left their record in the Don and Scarboro sections, that we have 

 certain evidence of changes of water-level, and this evidence refers to the 

 Ontario basin only. 



It may be that some will object to the assumption of an inter-Glacial 



* Since this paper was written copies of the Sixth Ann. Rep. of State Reservation at Niagara, 1890, 

 and of " Recent Earth Movement in the Great Lakes Region " have been obtained, giving valuable 

 information on this point. The isobasie curves on page G04 of the latter paper give a reason for 

 our difficulties in reducing tlie levels to the curve shown in the diagram. 



t F. B. Taylor : A short History of 'the Great Lakes, p. 20. 



