CONTAINING FLINT IMPLEMENTS, AND ON THE LOESS. 
305 
floods and inundations which would destroy their large contemporaries, but there is 
a limit to this power. Some land mollusks are not destroyed by immersion in water for 
days, and freshwater mollusks will revive after immersion in salt water ; but this applies 
to some species only, and with these, even, their mode of protection, although it might 
suffice for days, would not avail for a lengthened period. 
Although I may be quitting the strict limits of induction, I cannot conclude this 
paper without mentioning one impression which a review of the circumstances connected 
with the subject has made upon my mind. There is no doubt that great vicissitudes in 
the climate of any particular region may be caused by fluctuations in the isothermal 
lines resulting from changes in the relative distribution of land and water. But these 
fluctuations have a limit, which limit seems to me to have been greatly exceeded during 
the height of the glacial period. Looking at the special nature of such a remarkable 
reduction of temperature, closing as it were a vast cycle of anterior geological changes, 
and seeing its exceptional nature with reference to the general indications of higher 
temperatures which previously prevailed, I confess I feel deeply and strongly impressed 
with the probability that in this unexpected succession of changes we may trace evi- 
dence of great and all-wise design. If the cause were general (and there are strong 
reasons to believe that such was the case), the fact of the earth having been subjected 
to the severe and rigorous temperature of the glacial period must have led to a more 
rapid abstraction of heat from the surface than would have occurred without the inter- 
vention of a cold period, establishing, as it were in anticipation, a state of equilibrium 
which might otherwise have been indefinitely deferred had the refrigeration been gra- 
dual and uninterrupted; for on the removal or cessation of the refrigerating cause, 
the surface would be left in a condition to suffer for a certain period little or no further 
loss by radiation and no further contraction. The state of repose thus effected may 
have helped to impart to the earth’s crust that stability and immobility which render 
it fit and suitable for the habitation of civilized man. 
2 t 2 
