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Transactions of the Canadian Institute. 



[Vol. VII. 



in the vicinity of Haliburton are deep, so that the depth of the valley 

 bottoms below the level of the upland plain is frequently as much as 

 400 feet. The less-deep lateral valleys seem frequently to be graded 

 with respect to the lake surfaces. In some localities, in small areas 

 upon the upland, the topography is rolling, with only occasional low 

 ridges and shallow valleys, except close to the present lake depressions. 



Gradients. — The general even character of the skyline throughout 

 the crystalline area justifies a comparison of the arithmetic gradients of 

 the surface upon which the sediments rest, as ascertained by the 

 differences between the elevations of a number of localities within the 

 area. Data to institute a comparison along a series of parallel lines, 

 outside of the sedimentary area, are not available. Radially from the 

 upland surface in the vicinity of Haliburton lake to a number of points 

 along the base of the Cambro-Silurian escarpment, between Georgian 

 Bay and Kingston, the average gradient is nearly nine feet per mile. 



Figure i. — AB represents the plain beneath the sedimentary cover ; BC, the plain north of the edge of 

 the cover ; DB, the plain over the surface of the sediments ; a, the escarpment, b and c, outliers. Vertical 

 exaggeration about forty times. 



At Toronto the crystallines are known to be about 1,100 feet beneath 

 the present surface. Two other borings, one at Cobourg, and the other 

 in the township of South Fredericksburg, indicate that the floor is over 

 500 and over 600 feet, respectively, below the surface at these localities. 

 The average gradient beneath the sedimentary cover along a series of 

 lines from the foot of the Cambro-Silurian escarpment to the bottoms of 

 these borings indicates that the gradient beneath the cover varies from 

 twenty-two feet per mile in the western portion of the district to over 

 forty-one feet per mile at the eastern end. The relative attitudes of 

 these two surfaces are represented in figure i, where AB represents 

 the edge of a cross section of the plain beneath, and BC the edge of 

 a cross section of that outside the sedimentary area. 



Upon the surface of the sediments toward the eastern part of the 

 area, the gradient appears to lie between that beneath and that without 

 the cover (figure i, DB). In the vicinity of Toronto it, in part, 

 approximately coincides with that upon the surface of the crystallines 



