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Prof. J. Prestwich. On the Evidences of a [Mar. 9, 



with tlie main movements of upheaval. The last is remarkable from 

 the circumstance that the edges of the beds are turned over and 

 reversed in the same way that the " head " over the raised beach at 

 Portland is reversed. 



Passing on to the Channel Islands, a liaised Beach surmounted by 

 a "head" surrounds both Jersey and Guernsey, showing that in the 

 later glacial times, as now, those islands were separated from the main- 

 land. As the materials of the " head " — which is not a mere talus — 

 are all of local origin, they must have been carried down by an agent 

 acting in a quaquaversel direction from the centre of the islands, 

 where the hills form plateaux 300 to 400 feet high, often covered by 

 loam or loess. As there are no rivers to have originated the required 

 flood waters, this loess cannot have had a fluviatile origin, nor, as 

 there are no higher grounds, could it be the result of rain-wash, 

 neither can it be the result of the disintegration of the surface rocks. 

 It must therefore have had an origin different from that usually 

 ascribed to the loess, and which the author attributes to the deposi- 

 tion of sediment from the turbid sea-waters during submergence, 

 whilst the "head" results from the surface debris together with a 

 portion of this previously deposited sediment, swept off by divergent 

 currents during upheaval. 



The Loess. — After further reference to the phenomena on the west 

 coast of Prance, the author resumes the question which has given 

 rise to much controversy, namely, that of the origin of the loess, 

 which extends over such large tracts in Western and Central Europe. 

 That a certain section of it within valleys is due to river floods, 

 there can be no doubt, but there is another section, recognised as 

 such by most Continental geologists, to which it is not possible to 

 assign that origin. The latter is not confined to the river valleys, 

 but is found on the dividing water- sheds and on the high plains 

 separating the river basins. In the North of France it attains a height 

 of 400 to 600 feet, but in the neighbourhood of Lyons it reaches to 

 1300 feet, whilst in the great upper valleys of the Rhine and Danube it 

 attains to an altitude of 1500 feet, which is even exceeded further to 

 the east. It there covers the high plains of Hungary and Southern 

 Russia, and is by no means restricted to valleys and depressions on 

 the surface. Various theories have been proposed to account for this 

 wide dispersion of the loess, the two principal of which attribute 

 its formation : — 1, to a depression of Central Europe whereby the 

 gradient of the upper valleys was greatly reduced, while no change 

 of level occurred nearer the sea ; 2, to the advance of the great 

 northern ice sheet, blocking the large rivers of Eastern Europe, and 

 damming back their waters ; 3, to storm- winds acting upon disinte- 

 grated rock-surfaces. The author points out the objections to these 

 several views, and shows that such an accumulation of silt would 



