﻿GEOLOGY OF THOUSAND ISLANDS REGION I3I 



region. Only a little of this is within the map limits, in the ex- 

 treme southeast portion of the Theresa quadrangle. Such Trenton 

 as there is north of the river shows itself in rounded hills without 

 prominent in face and this is its normal and usual character. The 

 high cliff referred to is unusual and due to proximity to the Black 

 river. 



Minor modifications of these general features are produced be- 

 cause of the low folds of the Paleozoic rocks. The discussion of 

 these has shown how low domes and shallow basins are thus pro- 

 duced in the rocks, resulting in the formation of outliers and inliers 

 of the various formations, with their local infacing or outfacing 

 cliffs ; resulting also in a lobation of the general formational in- 

 facing fronts. As Ruedemann has stated these lobes are most con- 

 spicuous in the Leray fronts, an additional cause being there 

 at work to accentuate them. Nevertheless they are primarily due 

 to the folding, the other infaces showing similar, even though less 

 conspicuous lobes. The topographic maps show these general feat- 

 ures excellently. 



The lowlands of our region today are chiefly the result of the 

 stream wear during the Tertiary. ' The prominent rock infaces and 

 platforms of the various formations are owing to the considerable 

 differences in level between the low grounds and the adjacent up- 

 lands, and terrace broadly the ascents from the one to the other. 

 These features, together with those of the drainage outlined above, 

 were substantially what they are now at the end of Tertiary time. 

 There are few northern regions in which the general topography is 

 so little changed, and has its Tertiary features so little masked by 

 subsequent Pleistocene changes as is the case here. 



Lakes 



The group of lakes in the southeastern portion of the Alexandria 

 quadrangle, together with a few more of the same type in the dis- 

 trict to the eastward, constitute one of the very interesting features 

 of the district. Their interest arises in part from their localization ; 

 they are abundant in this restricted area and are scarce or lacking 

 elsewhere. In some features they resemble the much more abundant, 

 and more widely dispersed, lakes of central Ontario, as described 

 by Wilson ; in one respect they are sharply contrasted with them. 



Wilson describes the Ontario district as characterized by a prom- 

 inent cuesta front at the north edge of the Paleozoic limestones, 



