president's address. 25 



over the western nearly 1,400 feet, from which depression it slowly 

 recovered. By any such submergence Great Britain and Ireland would 

 be broken up into a cluster of hilly islands, between which the tide 

 from an extended Atlantic would sweep eastwards twice a day, its 

 currents running strong through the narrower sounds, while move- 

 ments in the reverse direction at the ebb would be much less vigorous. 

 The third interpretation, in some respects intermediate, was first ad- 

 vanced by the late Professor Carvill Lewis, who held that the peculiar 

 boulder clays and associated sands (such as those of East Anglia), which, 

 as was then thought, were not found more than about 450 feet above 

 the present sea-level, had been deposited in a great fresh-water lake, 

 held up by the ice-sheets already mentioned and by an isthmus, which 

 at that time occupied the place of the Strait of Dover. Thus, these 

 deposits, though indirectly due to land-ice, were actually fluviatile or 

 lacustrine. But this interpretation need not detain us, though the 

 former existence of such lakes is still maintained, on a small scale in 

 Britain, on a much larger one in North America, because, as was 

 pointed out when it was first advanced, it fails to explain the numerous 

 erratic blocks and shell-bearing sands which occur far above the margin 

 of the hypothetical lake. 



Each of the other two hypotheses involves grave difficulties. That 

 of great confluent ice-sheets creeping over the British lowlands 

 demands, as has been intimated, climatal conditions which are scarcely 

 possible, and makes it hard to explain the sands and gravels, sometimes 

 with regular alternate bedding, but more generally indicative of strong 

 current action, which occur at various elevations to over 1,300 feet 

 above sea-level, and seem too widespread to have been formed either 

 beneath an ice-sheet or in lakes held up by one; for the latter, if 

 of any size, would speedily check the velocity of influent streams. 

 Also the mixture and crossing of boulders, which I have described, 

 are inexplicable without the most extraordinary oscillations in the size 

 of the contributing glaciers. To suppose that the Scandinavian ice 

 reached to Bedfordshire and Herts and then retired in favour of North 

 British glaciers, or vice versd, assumes an amount of variation which, 

 so far as I am aware, is without a parallel elsewhere. So also the mix- 

 ture of boulders from South Scotland, the Lake District, and North 

 Wales which lie, especially in parts of Staffordshire and Shropshire, 

 as if dropped upon the surface, far exceeds what may reasonably be 

 attributed to variations amplified by lateral spreading of mountain 

 glaciers on reaching a lowland, while the frequent presence of shells in 

 the drifts, dozens of miles away from the present coast, implies a rather 

 improbable scooping up of the sea-bed without much injury to such 

 fragile objects, The ice also must have been curiously inconstant in 



