STRUCTURAL RELATIONS OF PRE-CAMBRIAN AND PALAEOZOIC. 
5 
the Thousand Island topography of the St. Lawrence, states that 
“The evidence is abundant, clear, and convincing that the 
Pre-Cambrian surface underneath the sandstone is precisely 
like that where the sandstone is absent, and that the present 
topography of the Pre-Cambric areas is that resulting from recent 
stripping away of the sandstone; in other words, that it is the 
reappearance at the surface of a topography of tremendous an- 
tiquity'’ “The relief of the Pre-Cambric surface 
under the Potsdam is much the same in character here as else- 
where along the northern and eastern borders of the Adiron- 
dacks, but is apparently less in amount than it is farther east, 
where there are differences in level of three or four hundred feet 
at least. 
“Where the Potsdam has been removed the Pre-Cambric 
surface disclosed is one of low ridges and valleys, with general 
northeast-southwest trend. The ridges are low with hummocky 
surface, and the valleys broad and shallow and developed on the 
weak rocks The extreme of relief does not much 
exceed 100 feet and is generally less.” 1 
In central Ontario, Wilson concludes that the Palaeozoic 
sediments “were laid down upon an uneven floor essentially the 
same as that presented at the present day by the Laurentian 
areas” 2 adjacent to the borders of the Cambrian and Ordovician 
rocks. 
Adams and Barlow describe the character of the topography 
and its relation to the structure in one of the areas adjacent to 
the Palaeozoic included in the Haliburton sheet, as follows: 
“A glance at the Haliburton sheet will show the remarkable 
influence which the strike of rock underlying the area has had 
upon the distribution and position of the lakes and upon the 
courses of the streams. In the southern portion of the area these 
follow very closely the course of the bands of Grenville limestone, 
while in the granitic region of the north they form a delicately 
etched pattern on the surface of the great plain of granitic gneiss, 
occupying shallow depressions whose course is determined chiefly 
1 H. P. Cushing, Geology of the Thousand Islands Region, Bull. N. Y. 
State Mus., No. 145, 1910, pp. 55, 60. 
a A, W. G. Wilson, Trans. Can. Inst., Vol. VII, 1904, p. 153. 
