172 Proceedings of the Boycd Physical Society. 



tion of climatic changes, therefore, must be reconsidered 

 from the point of view of the modern doctrine of the per- 

 manency of continental and oceanic areas. 



But before proceeding to this discussion, it may be well 

 to slance for a moment at the evidence from which it has 

 been inferred that the climate of the world has varied. 

 Among the chief proofs of climatic fluctuations are the 

 nature and distribution of former floras and faunas. It 

 is true that fossils are, for the most part, relics of extinct 

 forms, and we cannot assert of any one of these that its 

 environment must have been the same as that of some 

 analogous living type. But, although we can base no 

 aro^ument on individual extinct forms, it does not follow 

 that we are precluded from judging of the conditions under 

 which a whole suite of extinct organisms may have lived. 

 Doubtless, we can only reason from the analogy of the 

 present ; but, when we take into account all the forms met 

 with in some particular geological system, we seem justified 

 in drawinof certain conclusions as to the conditions under 

 which they flourished. Thus, should we encounter in some 

 great series of strata many reef-building corals, associated with 

 large cephalopods and the remains of tree-ferns and cycads, 

 which last from their perfect state of preservation could 

 not have drifted far before they became buried in sediment, 

 we should surely be entitled to conclude that the strata 

 in question had been deposited in the waters of a genial 

 sea, and that the neighbouring land likewise enjoyed a warm 

 climate. Again, should a certain system, characterised by 

 the presence of some particular and well-marked flora and 

 fauna, be encountered not only in sub-tropical and temperate 

 latitudes but also far within the Arctic Circle, we should 

 infer that such a flora and fauna lived under climatic 

 conditions of a very different kind from any that now exist. 

 The very presence, in the far north, of fossils having such a 

 geographical distribution, would show that the temperature 

 of polar seas and lands could not have been less than 

 temperate. When such broad methods of interpretation 

 are applied to the problems suggested by former floras and 

 faunas, we seem compelled to conclude that the conditions 



