288 NEOZOIC TIM3. [CHAP. XIII. 



outer parts of the great ice-slieets which had accumulated 

 over Scandinavia, Scotland, the Lake District, Wales, and 

 parts of Ireland, were brought within the reach of the 

 waves. As successive tracts of land and ice were carried 

 beneath the level of the sea, the ice would be broken up 

 into large noes and bergs, which, mingled with others 

 brought from the Arctic regions by the northern currents, 

 would form powerful agents of corrasion, propulsion, and 

 compression of material on any shores against which they 

 might be driven. 



During this phase of the period the material which had 

 previously been swept by glaciers out of the mountain 

 valleys on to lower ground would come under the action of 

 coast-ice and marine currents ; by these agencies it would 

 be re-arranged, much of it kneaded up into Boulder-clay 

 and spread out as wide sheets of that material, while other 

 portions were sorted into beds of loam, sand, and gravel. 

 It was probably by the action of coast-ice on subsiding 

 tracts of land that stones and boulders derived from sites 

 at comparatively low levels were carried up to the positions 

 where they are now found. 



It was at this time, too, and by the ordinary action of 

 waves on an exposed coast-line, that so much of Yorkshire 

 and Lincolnshire was destroyed, that the bay of the Wash 

 was formed, and a line of cliffs carved out of the eastern 

 side of the Chalk Wolds of Lincolnshire ; cliffs that were 

 afterwards battered into slopes by the impact of ice-floes, 

 and finally buried under the accumulation of Boulder-clay 

 which now conceals them. 



The opponents of the formation of Boulder- clays by 

 marine ice have often asked the upholders of that view to 

 point to the occurrence of deposits containing perfect and 

 undisturbed marine shells in association with Boulder-clay. 

 It is of course very seldom that such deposits would be 

 preserved, but the fossiliferous loams of North Lincolnshire 



