igoo-i.] Physical Geology of Central Ontario. 171 



case a broad open valley (Great Cataraqui) suddenly turns slightly and 

 narrows to a gorge cut in granite, through which the ice has passed. In 

 another case (Consecon creek, Prince Edward county) the present 

 creek heads on the upland and runs southwesterly, the valley gradually 

 broadening and deepening. About a mile to the east of its head the 

 Bay of Ouinte valley, (Plate III., fig. i) whose depth below the upland 

 at this place is 185 feet, cuts across at an angle of about fifty-five 

 degrees. 



These valleys are all, with the single exception of the gorge at 

 Kingston Mills, carved out of homogeneous limestones, lying in a nearly 

 horizontal position. Before the carving of the vallej's the country must 

 have been one of almost no relief. The adjacent region, from which the 

 ice came, is also one of low relief There arc thus no topographic 

 features which would cause the action of the sheet-glacier to be concen- 

 trated along certain lines which are oblique to its own general direction 

 of motion, and there is no reason wh}' these lines should sometimes 

 unite into one trunk valle}\ The expectation is that a sheet of ice 

 would under such circumstances tend rather to reduce than to accentu- 

 ate topographic features. This was true in this area in the case of 

 the second ice sheet, and has been shown to be true elsewhere, 

 and therefore is not an assumption as to a method of sheet-glacier 

 action. It is known that an ice stream, which invades a valley of sub- 

 aerial erosion tends to destroy the systematic arrangement of spurs and 

 re-entrants. That a sheet-glacier in a less confined area would tend to 

 erode systematic valley-systems more or less athwart its course seems 

 highly improbable.* 



On the contrary, their form and adjustments are appropriate to 

 stream erosion. Loose debris in the bottoms of the valleys near their 

 heads, pinnacles, and isolated outliers along the valley sides, are, how- 

 ever, almost completely wanting. Occasionally the present stream is 

 held back, forming a small pond, by the accumulation of a little drift 

 debris across a portion of the valley, or by a rock obstruction. Where 

 the tributary valleys join a main valley there is no discordance, or as 

 Playfair puts it, there is "such a nice adjustment of their declivities, 

 that none of them join the principal valley, either on too high or too 

 low a level ; a circumstance which would be infinitely improbable, if 

 each of these valleys were not the work of the (predecessor of the) 

 stream that flows in it." ('02, 102). 



The fact that these valleys are broadly open towards the southwest, 



*Compare with the valley of the Rhiie, Davis, 1900, p. 275. 



