8"24 THE GKOGRAFHIOAL SIOXIFICAXOK OF FLOODS, 



the less their vertical relief, and the wider the valleys the less 

 marked the cafton-convergences (as concerns heavy ice-thrusting), 

 and hence the less marke<i the resultant ice-thrusts. 



K.vamples. — Possibly Pat^onia and certain portions of Alaska. 

 The Highlands of Scotland, and the English Lake District afford 

 instructive examples of moi'^ m<xierate action. 



ii. The ict-sheet traversing area$ of mature to $en,Ue topogiiYiphy. 



The ice-sheet now, as it covers the land-forms, has g-eneral 

 directions of motion fi\)m its centres, but along those valle^^ only 

 whose main axes coincide with these directions will the glacially- 

 developed contours be similar and similarly situated. EacK 

 range and valley crossed by the icecap will now react on the 

 passing mass, just as boulders and other obstacles in stream- 

 channels react on the passing stream. And, heiv again, the 

 writer would insist on the careful examination of the small, and 

 easily understood stream-forms, so as to allow of correct reasoning 

 thence to the majestic ice-flood contoui^. Local eddies ai^ pro- 

 duced which, in each case, determine the conteui*^ at those spots. 

 The general direction of the ice-motion will, of course, be 

 unaltered, but local contours will l>e altogether inexplicable, 

 unless one has a clear understanding of the action of water- or 

 ice-ecidies set up by the channel-obstructions. 



Thus, imagine an ice-cap to be moving southwartis from a land- 

 mass, as shown at A in accompanjnng sketch, and crossing two 

 valleys B and C, se|varated by a high ridge PP, and partly con- 

 nected by a low col QQ, The vallej^ B face^ the east, and the 

 valley CGCH the wests As the ice-cap moved o\*er the high 

 separating ridge the general motion of the mass was towards the 

 south, but a lower ice-flow was set up easterly along the valley R 

 The col at QQ caused another local ice-eddy which, in turn, 

 swept westerly down the upper portion of the valley CGCH. A 

 cirque and basin ma}- thus be formed at the foot of the col ^^^ 

 with alignment of valley-wall masses as in direction indicated 

 by the arrows FF. All these forms are inexplicable on the 

 assumption of ice-cutting from north to south only. 



