ORIGIN OF BEDROCK TOPOGRAPHY 223 



In another locality on the second creek to the south of Chaumont creek, 

 in New York state, glacial striae on some meander spurs show that the 

 ice which made the striae moved across several meander curves deeply 

 cut into the limestone without materially modifying their outline. 



Some miles to the west of the particular area under discussion, along 

 the front of the Niagara escarpment, there are found a few outlying 

 areas, mesa-like, capped by Niagara limestone usually, that have not 

 been carried away by the ice. One of these is known as the Milton out- 

 lier and is completely severed from the main escarpment by a deep 

 ravine. Others of similar origin, with the valleys between them and 

 the main cuesta partly submerged, form the islands in Georgian bay 

 along the east coast of the Bruce peninsula. Other similar outlying 

 areas are found in many localities in front of the Black River escarp- 

 ment. Often it is found that in the rear of these outliers, when they lie 

 some distance in front of the cuesta, there is a long train of loose angu- 

 lar blocks which have been dragged off the top of the outlier by the ice 

 in its passage over the region. 



In very many localities between Trenton and the line of the Niagara 

 cuesta till sheets of several succeeding ice transgressions are found to 

 override the till of the earlier glacial transgressions and the stratified 

 gravels, sands, and clays of the several succeeding interglacial epochs. 

 In a number of cases, the best known being that east of Toronto, at 

 Scarboro, though several others occur farther east, it is known that 

 there was a period of erosion, during which broad valleys were carved 

 in the interglacial deposits which succeeded the lowest till sheets. The 

 ice-sheet which deposited the sheets of till other than the lowest trans- 

 gressed these valleys cut in the interglacial deposits, and in some cases 

 partly filled them with till. In descending into them it seems to have 

 created little or no disturbance of the underlying soft materials. In 

 ascending on the opposite side it has crinkled and crumbled some of 

 the strata where there were competent clay members to carry the thrust 

 for some little distance back from the side of the valley in question 

 In no case does it appear to have seriously modified the preexisting 

 topography by extensive erosion of these soft deposits. 



The relations of the various till-sheets and interglacial deposits between 

 Trenton and Hamilton show that during the times of transgression of 

 the ice, other than the first, it passed over very soft deposits, some of 

 which lie within the valleys under discussion, without materially de- 

 stroying by erosion the preexisting topography of these soft deposits. 

 From this alone we might infer it would be highly improbable that the 

 ice of the earlier period would have performed any more effective work 

 on the bedrock topography. As has been shown, the bedrock features 



