No. 4.] DAWSON — POST-PLIOCENE. 413 



sweeps it, with the simihir material of many other Alpine streams, 

 into the Mediterranean, to aid in filling up the bottom of that 

 sea, whose blue waters it discolours for miles from the shore, 

 and to increase its own ever enlarging delta which encroaches on 

 the sea at the rate of about half a mile per century. The upper 

 waters of the Rhone, laden with similar material, are filling up 

 the Lake of Geneva ; and the great deposit of ' loess' in the 

 alluvial plain of the Rhine, about which Gaul and German have 

 contended since the dawn of European history, is of similar 

 orio-in. The mass of material which has thus been carried ofi" 

 from the Alps, would suffice to build up a great mountain chain. 

 Thus by the action of ice and water — 



" The mountain falling cometh to naught 

 And the rock is removed out of its place." 



" Many observers who have commented on these facts have 

 taken it for granted that the mud thus sent off from glaciers, and 

 which is so much greater in amount than the matter remaining 

 in their moraines, must be ground from the bottom of the glacier 

 valleys, and hence have attributed to these glaciers great power 

 of cutting out and deepening their valleys. But this is evidently 

 an error, just as it would be an error to suppose the flour of a 

 grist-mill ground out of the mill-stones. Glaciers it is true 

 groove and striate and polish the rocks over which they move, 

 and especially those of projecting points and slight elevations in 

 their beds, but the material which they grind up is principally 

 derived from the exposed frost-bitten rocks above them, and the 

 rocky floor under the 2;lacier is merely the nether mill-stone 

 against which these loose stones are crushed. The glaciers in 

 short can scarcely be regarded as cutting agents at all, in so far 

 as the sides and bottoms of their beds are concerned, and in the 

 valleys which the old glaciers have abandoned, it is evident that 

 the torrents which have succeeded them have far greater cutting 

 power." 



" In conclusion, I would wish it to be distinctly understood, 

 that I do not doubt that at the time of the greatest post-pliocene 

 submergence of Eastern America, at which time [ believe the 

 greater part of the boulder clay was formed, and the more im- 

 portant striation effected, the higher hills then standing as 

 islands would be capped with perpetual snow, and through a 

 great part of the year surrounded with heavy field and barrier 



