﻿XCiv PEOCEEDIK-GS OF THE GEOLOGICAL SOCIETY. [May I908. 



of the boulder-drift. Yet he still clung to the notion that during 

 the time of submergence 



' currents produced by repeated elevatory movements not only swept away 

 new sedimentary deposits, but also still more deeply excavated the pre-existing 

 valleys.' (Q. J. vol. viii (1852) p. 20.) 



In spite, however, of these efforts to support it, the paroxysmal 

 explanation of the northern drift was slowly but surely being 

 exploded in this country by the progress of more extended and 

 detailed study of the drift and dressed rocks, though it continued 

 to maintain its sway on the Continent. When English geologists 

 dropped it as a possible aid in the interpretation of the striated 

 rock-surfaces and the boulder -drift, they fell back, not on the 

 explanation offered by Agassiz, but on submergence and icebergs. 

 The hypothesis of floating ice, wdth or without the aid of sub- 

 terranean paroxysms, continued for nearly twenty years after 

 Agassiz's visit to be the generally accepted method of accounting 

 for the facts. Yet during those lean years of progress in this part 

 of British geology a few able observers, notably Kobert Chambers 

 among them, advocated the claims of land-ice to attentive con- 

 sideration. Their appeal to the evidence of the polished and 

 grooved rock- surfaces, to the divergence of the strige from the 

 central uplands, and to the radiation of the boulders from these 

 centres of dispersion met with little heed, until about the year 1860 

 a marked revival of interest in the subject set in. Some new and 

 active investigators, following the example of Chambers, began to 

 study the phenomena in more detail than had been done before. 

 They ascertained beyond all question that the dressed rock-sui'faces 

 must have been produced by some agent that not merely rubbed 

 them down, but moulded itself upon their uneven surfaces, and, 

 diverging on ever}^ side from the higher grounds, moved steadily 

 across the surrounding lowlands regardless of their minor topo- 

 graphical features. It was found that the erratic blocks followed 

 the same lines of radiation. The whole of the appearances seemed 

 to be inexplicable by the capricious movements of bergs and floes 

 variously driven by winds and currents. These floating masses of 

 ice might conceivably grate along submerged rocks, but could never 

 descend into each hollow and mount over each protuberance of the 

 roches moutonnees. The only theory which would explain all 

 the facts was recognized to be that proposed by Agassiz twenty years 

 before, that not merely local glaciers occupied the valleys among our 

 mountains, but that these mountains, like those of Greenland, were 



