404 Mr. S. V. Wood on the Belgian Equivalents of 



I know, yielded no proper fossils, its included organic remains 

 being wholly derivative*. In Belgium, the only fossils obtained 

 fromtheLoess appear tobeof fluviatile,or rather terrestrial habitat; 

 and it is the presence of these latter, doubtless, that has chiefly 

 contributed to deter geologists from referring the Loess to the ho- 

 rizon of the Boulder-clay. Speculations on the agencies producing 

 these discordant features have not much to rest upon ; but we 

 may not unreasonably take into account the influence of the arctic 

 conditions of the period as either causing or contributing to this 

 result. The views of geologists have already been expressed in 

 favour of a great freshwater discharge down the valley of the Rhine 

 as the cause of the deposit of the Loess, although they have dif- 

 fered as to the mode in which the fresh water was distributed. 

 It appears to me, however, that in the gorge of the Rhine we 

 should, under arctic conditions, have one of those deep fiords, 

 described by Dr. Sutherlandf as so fertile in glacier produc- 

 tion, that now indent Baffin^s Bay, with the added condition of 

 its being the outlet of the drainage of a considerable tract of land. 

 If a great difi^erence between the temperature of summer and 

 that of winter prevailed during the Loess period, more resembling 

 the climate at the mouth of the Mackenzie and Coppermine Rivers 

 than those of the eastern side of America, very extensive floods 

 of fresh water would be poured down the valley of the Rhine 

 during summer, and spread over a considerable area at its 

 mouth. Whether this periodical disturbance of the distribu- 

 tion of fresh and salt water over the region near the point of 

 discharge would render the area unsuited alike for the habita- 

 tion of marine, of fluvio-marine, and freshwater mollusks is 

 uncertain : a better knowledge than is yet possessed of what 

 now obtains, under circumstances presenting the nearest analogy 

 at the present day, is required before a satisfactory reply can be 

 given ; but it has occurred to me as not improbable that, since 

 the included Mollusca of the Loess are of that habitat that they 

 may well have been carried down from swamps or rills exist- 

 ing high up the Rhenish country, or among the higher eleva- 

 tions of the Ardennes, and sparsely distributed with the muddy 

 sediment over the Loess area, such a state of things might 

 furnish an explanation of the absence of either fluvio-marine or 

 of purely marine Mollusca. The intermittent volume of the 

 freshwater discharge would, I conceive, produce conditions 

 quite diff^erent from those ordinarily understood as fluvio-marine, 



* I am permitted by Mr. J. G. Jeffreys to state that he has recently 

 obtained marine molluscous remains from what he regards as undoubted 

 Boulder-clay of the Yorkshire coast. 



t Quart. Joum. Geol. Soc. vol. ix. p. 30. 



