216 A. W. G. WILSON — TRENT RIVER SYSTEM 



the upland or intervalley areas north of lake Ontario is to the south, or 

 toward the lake. All the present valleys north of lake Ontario, which 

 have been cut in the limestone, slope toward the southwest — not, how- 

 ever, always in accordance with the dip, though they are in accordant 

 positions with each other. Hence the grade of the valley bottoms is 

 much less than the slope lakeward from the Archean areas, the length 

 of the valleys being thus proportionally longer than the line of maxi- 

 mum slope from their heads near the Archean to the nearest part of the 

 lake into which flow the streams occupying the bottoms of the valleys. 

 The direction of flow of the present streams is not that which they would 

 normally assume in consequence of the slope of the general surface of 

 the country. 



In New York, on the other hand, the dip of the slope-plane of the bot- 

 toms of the valleys is in nearly the same direction as that of the plane 

 of the dip, and that of the plane of the upland surface, but the three 

 different planes are at slightly different angles to the horizon, that of the 

 dip being greatest, and that of the valley bottoms least. In Ontario the 

 direction of slope of the valleys is in a direction accordant with the sim- 

 ilar valleys developed to the south of the Saint Lawrence in New York. 

 In Ontario these differences in direction of slope between the general 

 surface, the plane of the valley bottoms, and the plane of the dip are so 

 well marked in places that in the field the discordances can readily be 

 rcognized by the eye alone. 



Subsequent to their planation the limestone areas must have been 

 uplifted and partly dissected, as in their present attitude we find that 

 they present a well marked cuesta front toward the old land, and are 

 dissected by a well developed system of valleys to whose existence refer- 

 ence has already been made. The valleys and the lowland in front of 

 the cuesta are regarded as of later date than the plane which bevels off 

 the upland surface, since there is everywhere a well marked discordance 

 between the gradient curves of the valley sides or cuesta front and the 

 very much flatter surface curves of the even uplands. 



The cuesta front as it now appears is often a steep, inaccessible cliff. 

 The height varies up to a maximum of about 150 feet. The crest of the 

 cuesta is usually formed by heavy-bedded Black River limestones. At its 

 base there are often found softer calcareo-arenaceous, at times argillaceous, 

 beds. These latter, or else sandstones of Potsdam age, often underlie the 

 narrow belt of lowland which lies in front of the cuesta, between it and 

 the oldland. In Ontario the lowland in front of the cuesta is also fre- 

 quently located on Archean rocks. These lowland areas often form 

 basins, in which are located small, shallow lakes. 



The valleys which lie on the limestones are of two types — those which 



