PHYSICAL AND CLIMATAL CONDITIONS. 143 



Such peculiarities of distribution serve to show the 

 effects of even comparatively small changes of level upon 

 climate, and upon the distribution of life, and to confirm 

 the same lesson of caution in our interpretation of local 

 diversities of fossils, which geologists have been lately 

 learning from the distribution of cold and warm currents 

 in the Atlantic. Another lesson which they teach is the 

 wonderful fixity of species. Continents rise and sink, 

 climates change, islands are devoured by the sea or 

 restored again from its depths ; marine animals are locally 

 exterminated, and are enabled in the course of long ages 

 to regain their lost abodes ; yet they remain ever the 

 same, and even in their varietal forms perfectly resemble 

 those remote ancestors wliich are separated from them by 

 a vast lapse of ages and by many pliysical revolutions. 

 This truth which I have already deduced from the Pleis- 

 tocene fauna of the St. Lawrence valley, is equally 

 taught by the molluscs of the Acadian bay, and by their 

 Arctic relatives returning after long absence to claim 

 their old homes. 



Still another lesson may be learned here. It appears 

 that our present climate is separated from that of the 

 glacial age by one somewhat warmer, which was coinci- 

 dent with an elevated condition of the land. Applied to 

 Europe, as it might easily be, this fact shows the futility 

 of attempting to establish a later glacial period between 

 the Pleistocene and the present, in the manner 

 attempted, as I must think on the slenderest possible 

 grounds, by Prof. Geikie in his late work "The Great 

 Ice Age." 



The grandeur of those physical changes which have 

 occurred since the present marine animals came into 

 being is well illustrated by some other facts to which our 



