310 E. C. ANDREWS. 



force. The lines of least resistance are followed. In this 

 case the lines of least resistance followed by the stream as 

 a whole are those of quickest descent. 



But the fact must not be lost sight of that the ability of 

 a stream to corrade its channel structures is related in a 

 highly increasing ratio to increase of stream velocity. 

 Therefore if an ice sheet has been enabled to scour the 

 New York plain as efficiently as it appears to have done, 

 then it follows that the Hudson River channel, sunken into 

 this plain, has been subjected to a much more powerful ice 

 action. But this would result both in the great deepening 

 of the channel and the more or less complete removal of 

 spurs with the production of steep and straight valley sides. 



5. St. Lawrence River at Quebec— This case is similar 

 to that just discussed for the Hudson at New York. 



6. England, Wales, and Scotland— Snowdon (North 

 Wales) 1 — The general topographic features of North Wales 

 as seen during a visit to Snowdon via Rhyl are : — 



(i) An old surface represented now by isolated peaks and 

 ridges of which Snowdon is an example. 



(ii) A broad upland valley or younger peneplain due to 

 the action of ordinary streams and occurring at heights 

 apparently from 1,000 to 2,000 feet above sea-level. This 

 is the peneplain referred to by Davis. 



(iii) A series of broad mature valleys developed in the 

 old upland valley level. These younger valleys are of the 

 44 valley in valley " type and represent periods of river 

 revival consequent on land elevation. 



(iv) A younger plain of marine (?) erosion and now 

 elevated to form a land block of which the Isle of Anglesey 

 is an example. 



1 For a much fuller account of the glaciation and general topography 

 of this locality see Davis, W. M., quoted under literature. 



