i68 Transactions of the Canadian Institute. [Vol. VII. 



rock floor and the youngest till sheet. The inability of the sheet- 

 glaciers, under certain unknown conditions, to remove this material 

 during the two last periods of transgression, raises the question as to 

 whether these conditions may not have existed also during the period of 

 operation of the first ice sheet, when it was overriding bed rock instead 

 of soft sands and clays. This question can in part be answered by a 

 study of the bed rock features. 



Eastern Rock- Valleys. — The eastern boundary of the moraines is 

 approximately a line running northeast from Trenton to a point 

 just south of Croyden in the northern part of the township of Camden, 

 Addington county. East of this line in the southern part of the county 

 of Hastings, in Prince Edward, in Lennox and Addington, and in Fron- 

 tenac, the topography of the underlying rock surface is but little 

 concealed, large areas of almost bare limestone are quite common. 

 This is also essentially true of the rock topography along the margin of 

 the Black River cuesta between Mud Turtle lake and Kingston, with 

 the exception of a narrow belt in part of Huntingdon and Hungerford 

 townships. 



In the eastern counties the drift cover is very thin, and rock valleys, 

 now occupied by streams, can be followed readily from their outlet on 

 Lake Ontario or the Bay of Quinte, more or less completely across the 

 limestones towards the Archean. In these counties there are six at 

 least which can be followed all the way across, each to a long narrow 

 lake whose limestone scarped basin is floored with crystalline rocks. 

 There are many more which reach nearly across (Map II). From a 

 map study of Jefferson county, New York state, it seems probable that 

 at least some of the streams in that state belong to this category. The 

 whole series of valleys, some twenty-five and more, is remarkable for its 

 parallelism, the general direction being southwest, and for the regular 

 spacing of the streams. The valley depressions of some are readily 

 traceable under the lake waters, with some complications, to a line 

 running between Stony Point and Point Peter, and in some cases 

 beyond. Where these valleys are unsubmerged, their sides, at the 

 lower ends, are generally steeper on the southeast, towards which the 

 rocks dip, and less steep, sometimes broadly open, on the northwest. 

 Towards the upper end, especially in the case of those which reach the 

 Archean highlands, the valleys are sometimes still broad, but both sides 

 are of about equal altitude and steepness. The average depth is about 

 one hundred feet, locally often much more, and rarely less, except in 

 the smaller valleys. Towards the lower end the width varies to about 

 five miles, while at the upper ends they are usually much narrower. 



