PKESIDENTIAL ADDRESS. 547 



Goodcliild, ill his luminous description of the glacial deposits in the Vale of Eden,^ 

 and his conclusions have been supported hy the researches of Dr. N. 0. Hoist in 

 Southern Greenland, where there was found to be the same diflFerence between 

 the unoxidised ground-moraine and the overlying oxidised material of 

 ' englacial ' origin as between the lower and upper boulder-clays in areas of 

 ancient glaciation.^ In adopting this explanation we must recognise that the 

 uppermost boulder-clay of an extensive area was not formed at exactly the same 

 time in every part, but was accumulated progressively as a marginal residue 

 during the emergence of the land from its icy cloak. 



Late Glacial and Tost -Glacial Deposits. — Of the glacial and iuterglacial 

 epochs of Professor Geiljie's scheme later than the * Polandian ' it is admitted 

 that no indication has been found in Yorkshire. There seems, on the con- 

 trary, to be evidence of steady amelioration in the climate, as tlie glacial 

 deposits opposite the mouths of the Wold valleys are overlain, first by 

 great deltas of chalky gravel, denoting torrential floods, probably from 

 the seasonal melting of heavy snows ; and then, in the hollows of these 

 gravels, or of the boulder-clay itself, we find freshwater marl and peat that 

 were deposited in the many lakelets and marshes that dotted the Holderness 

 plain; and in the lower layers of certain of these freshwater deposits the leaves 

 of the arctic birch (Bctula na7ia) have been detected,^ indicating a climate colder 

 than at present. 



In East Yorkshire, then, we appear to have a continuous record,of the events 

 from the beginning to the end of the Glacial Period ; and yet, if I read the 

 sections aright, we can find no place into which a single mild iuterglacial epoch can be 

 intercalated. 



Let us now more briefly consider certain glaciated areas within the influence of 

 th© * West British' ice-lobe which I have personally investigated. 



Drifts of the Isle of Man. — From its isolated position in the midst of 

 the Irish Sea, the Isle of Man constitutes an excellent gauge or glaciometer, on 

 which is recorded the course of events within the basin occupied by the West 

 British ice-lobe. In carrying out the geological survey of this island I made a 

 close examination of its glacial deposits in every part, and have stated the 

 results rather fully in a recently published memoir.* 



We find here, as in Yorkshire, that prior to the glaciation there was a sea- 

 margin at approximately its present level and, where the coast is composed of 

 'solid ' rocks, in approximately its present position. In this sea, marine deposits 

 indicative of cold conditions were accumulated, and were afterwards displaced 

 and mingled with the boulder-clay of an ice-sheet that gradually filled the basin 

 and swept southward, or south-south-eastward, over the very summit of the 

 island. At its maximum the surface of this ice-sheet stood more than 2,000 feet 

 higher than present sea-level. The difference between the altitude attained 

 by this ice and that of the East British lobe in the same latitude is especially 

 noteworthy. In Yorkshire the eastern ice did not reach much above 800 feet 

 on the flanks of the Cleveland Hills, declining to 500 feet or under off 

 Flamborough Head. The higher land which surrounds the Irish Sea Basin may 

 be in part responsible for this difference, but I think that it must have been 

 mainly due to the heavier precipitation in the west. 



Then followed a declining stage in the glaciation, during which the ice-sheet 



' ' Ice Work in Edenside.' Tram. Cumherland Assoc., No. 12 (1886-7), pp. 111- 

 167. 



" ' Dr. N. O. Hoist's Studies in Glacial Geology,' by Dr. J. Lindahl, American 

 Naturalist, Aug. 1888, pp. 705-712. It should be noted, however, that Professor 

 R. D. Salisbury did not find this difference apparent in the moraines of North 

 Greenland glaciers. See Journ. Geol, vol. iv. (1896), pp. 806-807. 



' By Dr. A. G. Nathorst, at Bridlington ; and by C. JReid, at Holmpton. Geology 

 pf Holderness, pp. 78 and 85. 



* ' The Geology of the Isle of Man ' (1903). Mem. Geol Survey. 



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