240 A. W. G. WILSON — TRENT RJVER SYSTEM 



The investigations as to the history of this portion of the stream are not 

 yet sufficiently advanced to warrant extended discussion at this time. 



Summary and CoiNclusions 



In writing the foregoing description of the topography of the country 

 bordering the east end of lake Ontario, it has been necessary to omit 

 reference to many interesting minor details. In the majority of cases 

 only those features which seem to bear directly on the question of the 

 origin of the Saint Lawrence outlet, and on the problem of the origin 

 of the principal features of the region, have been described and dis- 

 cussed. It remains but to summarize the results of the foregoing study. 



In the first place, the balance of evidence with regard to the amount 

 of erosion by the ice-sheets which transgressed this region is distinctly 

 in favor of the conclusion that this erosion was very slight. The main 

 points on which this conclusion is based are: 



1. The unquestioned fact that the ice-sheets which succeeded the 

 earliest sheet whose till rests on the bed-rock overrode soft stratified 

 and unstratified deposits which were the work directly or indirectly of 

 the earlier ice-sheets, without materially altering the preexisting form, 

 in so far as the evidence of the numerous cross-sections shows what that 

 form may have been ; from this it is inferred that there is little likelihood 

 of the first sheet having been a more effective erosive agent. 



2. The topographic features are similar to those produced by stream 

 erosion in unglaciated regions, and bear no definite relation to the direc- 

 tion of the ice movement. On the contrary, their systematic develop- 

 ment quite independently of that movement, accurate adjustments even 

 to small details, and retention of characteristic forms show that the 

 amount of erosion by the ice was very limited. They antedate the 

 period of ice-transgression, at whose close the earliest till sheet was de- 

 posited, and by which the striations on the bed-rock beneath that till 

 sheet were produced, as is evidenced by the occurrence of both the till 

 and the striations in the valleys as well as on the uplands. 



That the complicated system of valleys here described is due to stream 

 erosion is inferred, as already stated, from their similarity in form and 

 adjustments to valleys produced by stream erosion elsewhere in ungla- 

 ciated regions. The direction of flow of the streams which carved them 

 is inferred to have been southwest because uniformly throughout the 

 system the valleys are found to become wider, frequently deeper, and 

 always more mature in form as one proceeds from their heads on or near 

 the inner lowland outward toward the region to which they now drain. 



The main stream of the Trent River system is seen to alternately flow 

 in a new channel of post-Glacial origin and in a course along an ancient 



