GENERAL TOPOGRAPHIC FEATUAES 215 



thus producing a series of small lakes bordering the eastern end of lake 

 Ontario. 



Topographic Features of the Country East and Northeast of 



Lake Ontario 



general description of the topography 



The topography of the portion of the area underlain by Archean rocks 

 is that of one of the partly dissected pre-Ordovician facets of the Lau- 

 rentian peneplain.* In this particular locality it is characterized by 

 the occurrence of longitudinal, often steep-sided, more or less rounded 

 or domed ridges, with deep valleys between, characteristic of the Archean 

 areas where they are bordered by the Paleozoics. The maximum relief 

 rarely exceeds 150 feet. The lower portions of the depressions often 

 form lake basins, and the longitudinal valleys are usually the basins of 

 streams. A reference to the accompanying areal map (plate 5) will 

 show the general longitudinal distribution of the water bodies, which, 

 in the absence of contour topographic maps, will serve as a valuable 

 index to the nature of the topography. 



In detail it is found that between the major longitudinal valleys of 

 the Archean areas the general surface of the tops of the intervalley ridges 

 (where these are not too narrow) is mammillated or undulating. Every- 

 where the tops and often the sides of the ridges have been smothered 

 and scoured, and all now present a surface of relatively fresh rock. As 

 has been pointed out elsewhere,f the main topographic features, includ- 

 ing this last characteristic, are probably in all their essential features of 

 pre-Ordovician date. 



The Ordovician limestones lie with a very gentle dip away from the 

 Archean areas. North of the east end of lake Ontario the dip is ap- 

 proximately southwest. East of lake Ontario it is more westerly. Espe- 

 cially near the Archean regions there are local undulations and other 

 irregularities caused by the unevenness of the floor on which the sedi- 

 ments were laid down. Subsequent to their deposition and before the 

 present drainage lines were developed, erosive processes planed off the 

 region, producing a nearly even surface, truncating the beds at a slight 

 angle both with the dip and with the line of strike, leaving the imbri- 

 cating edges of the different beds pointing toward the old land. That 

 surface has now become somewhat warped, the lowest part being in the 

 vicinity of the valley of the Saint Lawrence river. The general slope of 



*A. W. G. Wilson : The Laurentian Peneplain. Chicago Journal of Geology, vol. xi, 1903, p. 615 

 et seq. 

 f Chicago Journal of Geology, loc. cit., p. 656. 



