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in the main, been able to hold off the invading ice ; but occasion- 

 ally, the upper platform of the ice (while the lower platforms still 

 maintained their normal direction of flow,) would move inwards 

 towards the heart of the mountains (when the pressure exerted by 

 the extraneous ice overcame the local resistance). Sometimes this 

 took place even in directions diametrically opposite to those taken 

 by the ice lower down. The result was that while the lower 

 currents carried local detritus outwards, the higher currents trans- 

 ported material of other kinds in nearly the opposite direction ; 

 and so, the material dispersed throughout the ice over that par- 

 ticular spot included boulders whose direction of transportal was 

 nearly diametrically opposite to that of those movements of the 

 sole of the ice that effected the glaciation of the rock. 



The Melting of the Ice, and its attendant Phenotnena. — This leads 

 to the point I have been for some time aiming to reach, viz : — 

 (i) That the chief glacial erosion of the district was accomplished 

 mainly in the long period preceding the climax of the Glacial 

 Period. (2) That the glacial markings and striae now existing 

 represent only the last movements of the ice, and therefore date 

 mainly from the climax. (3) That the distribution of the boulders 

 represents the nett result of all the causes acting upon the boulders 

 from the commencement of the Glacial Period down to its very 

 close, largely modified by the very last movements that took place 

 before the ice began to melt. It was the melting of the ice, and 

 the consequent liberation of its contents there and then, in the 

 form of sediment (which was sometimes modified by the action of 

 running water) that gave rise to the various forms of drift here. 

 Some of the phenomena attendant upon this melting of the ice 

 sheet may conveniently be reviewed at this point. 



Relation of External Configuration of Drift Mounds to the Rock 

 Surface beneath. — Amongst the phenomena above referred to, one 

 of the most curious was pointed out to me in 1872 by my colleague 

 Mr. Aveline ; and had been noticed, I find, also by Mr. Macintosh, 

 and others. This is, that the external configuration of a mound 



