﻿lxxviil PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May I905, 



not be tolerated at the present day in any other branch of science, 

 and it is time indeed that the stratigraphical geologist should apply 

 himself to his own branch of work with the assiduity and attention to 

 detail which are now expected of the palaeontologist in the museum. 



(6) Climatic Changes. 



Of all the recent changes with which the meteorologist has to 

 deal, the most regular are those variations of temperature which 

 are due to extra-terrestrial causes. An area may be subjected to 

 fog, tempest, or drought, owing to irregular meteorological changes ; 

 but, apart from these, we have constaut diurnal and summer heat, 

 constant nocturnal and winter cold. Less regular, though still, so 

 far as we can judge from the scanty data at our disposal, recurring 

 with some approach to constancy, are such temperature-changes as 

 are indicated, for example, by the alternate periods of advance and 

 retreat of glaciers. 



The question naturally arises : were there not in past ages even 

 more important cases of climatic recurrence, of which each phase 

 may have existed through long periods of geological time ? This 

 is, at any rate, suggested by the widespread occurrence of glacial 

 conditions in the Permo-Carboniferous Period, and by the existence 

 in so many areas of Tertiary deposits, showing a gradual diminution 

 of temperature from early Tertiary times to the culminating stage 

 of cold of Pleistocene date. If such recurrence happened as the 

 result of important extra-terrestrial changes, we should expect its 

 effects to be more widespread than those which were caused by 

 terrestrial changes ; it is important, therefore, to collect evidence 

 bearing upon this question. I cannot help believing that the 

 changes noted when studying the geogram, both as regards litho- 

 logical characters and faunas and floras, sometimes possess so 

 extended a geographical range that ordinary terrestrial change is 

 insufficient to account for them. I have again and again been 

 struck with similarities, difficult to put into words, between the 

 lithological characters of various Lower Palaeozoic sediments from 

 many parts of the Old and New Worlds, which would suggest the 

 general age of the deposits, even if we could not corroborate the 

 inference by examination of the included organisms. 



We also find examples of variation of fauna occurring during 

 shorter geological periods, which in the present state of our know- 

 ledge seem most readily explicable by climatic change, though I must 



