4.04. 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’ 
fromthe Loess appear tobe of 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. Sutherland+ 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 difference 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 different 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. 
+ Quart. Journ. Geol. Soe. vol. ix. p. 30. 
