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MR. PRESTWICH ON THE GEOLOGY OF THE DEPOSITS 
cient data, whether any of the perturbations in the increment of heat at different places 
and depths within this area may not be due to the circumstance of a very much lower 
temperature having prevailed here at an antecedent period*'; and whether, if so, the 
date of that period (taking that of the extreme glacial cold) could not be fixed within 
a certain limit, by the application to this investigation of the known laws regulating 
the transmission of heat through solid bodies. 
The uninterrupted succession of life from this postpliocene period to our own time 
cannot fail to have been noticed in the course of this inquiry — a succession so large and 
so important, that it is not possible to contemplate the occurrence of any intervening 
catastrophe of such a nature as to destroy the life of the period, and seek for an expla- 
nation of its return by immigration from adjoining districts. Apparent even as the 
connexion is in the limited ground we have studied, it is infinitely stronger when the 
whole series of pliocene and postpliocene deposits comes under review. Even in the 
aspect here presented the conclusion is inevitable, that no general cause has led to the 
extinction of life over this part of Europe at any recent geological period. There have 
been great river-floods and great changes, but no interruption in the succession of life 
from the time of the great extinct mammals to our own times. There are still serious 
difficulties in the way of explaining the cause of the disappearance of so many of these 
large Mammalia ; but a sufficient number remain to attest the direct descent of a portion 
of the old fauna to our day. The Reindeer, the Bos primigenius , the Aurochs, are 
amongst those which survived all the successive changes f. Why the larger Pachyderms 
should not also have survived we cannot explain, we can only admit the fact, which is 
the more remarkable from the non-extinction of other classes. The change of climatal 
conditions could scarcely have been the sole cause, as that would affect one class equally 
with the other ; and besides, as the climate at this time presented no extreme character, 
they could, as the changes progressed, have found, by migration or limitation, as with 
the other animals, places still adapted to their former condition. But by far the most 
remarkable and convincing feature in the case is the transmission from the quaternary 
period of so large a proportion of the small and delicate land and freshwater shells. Not 
only are they found inhabiting the same land as formerly, but their distribution follows 
very much the same law. More than two-thirds of our recent species are found in a 
fossil state ; and when we consider that the list of living species is the result of close 
examination of numerous observers for a series of years over a large extent of country, 
whereas that of the fossils is the result of a necessarily limited search at very few 
places, where they are buried in the ground and rendered fragile by age, it is rather 
a matter of surprise that the collection should be already so large. Many of these 
mollusks will no doubt live for a time out of their element, and they might survive 
* I apprehend that some of the calculations that have been made on the earth’s temperature and refrigeration 
may also be affected by this disturbing cause. 
+ On this subject M. Pictet of Geneva has made some interesting observations in a paper published in the 
‘ Archives des Sciences de la Bibliotheque Universelle’ for August 1860. 
