414 M. ADHE"MAR ON CHANGES IN THE SEA-LEVEL. 



tude of Glasgow. A mile of ice removed in the same wav 



O / 



would produce a change of 280 feet. M. Adhemar dwells 

 on various considerations which induce him to attribute a 

 very great thickness to the great southern glacier, and con- 

 sequently he considers that the alterations of sea-level which 

 would result from the alternate preponderance of ice in the 

 Arctic and Antarctic regions, would account for the various 

 alterations in the distribution of land and water. That there 

 must, however, have been elevations and depressions of the 

 land itself is sufficiently evident from other considerations; 

 but it is impossible to deny that the cause pointed out by 

 M. Adhemar may have produced the relative elevation of the 

 sea, as proved by the various raised beaches which fringe our 

 shores, and the depression on the other hand indicated by the 

 submerged forests, observed at so many points. 



The former would indicate the periods of cold ; the latter, 

 those of heat. The present condition of our rivers will also 

 thus be simply explained. There can, I think, be no doubt 

 that many of them have excavated their own valleys. At 

 present, however, they are all filling up the lower parts of the 

 excavation, as, for instance, we have seen to be the case with 

 the Somme. 



Moreover, the bottom of these valleys is in most cases lower 

 than the present sea-level, which cannot have been the case 

 at the time when they were excavated. It is evident, then, 

 that the excavation must have been finished at the time when 

 the sea was at a lower relative level than at present. 



Again, it will be remembered that side by side with the 

 remains of Arctic animals have been found others indicating a 

 warm climate, such, for instance, as the hippopotamus. This fact, 

 which has always hitherto been felt as a difficulty, is at once 

 explained by Mr. Croll's suggestion ; for when the excentricity 

 was at a high value, we should have a change every ten or 

 twelve thousand years from a high to a low temperature, and 



