The Glacial Theory, 



of stratification. We actually observe something of a similar kind, on 

 a small scale, in the oscillations that occur in the extremity of gla- 

 ciers which sensibly advance and retreat ; as, for example, under the 

 extremity of the lower glacier of the Aar in the Grimselgrund ; and, 

 among the localities where glaciers no longer exist, I may cite the 

 lower extremity of Log Treig, and the neighbourhood of Muckairn, 

 between Loch Awe and Loch Etive. 



In order to explain the whole of the facts relative to the erratic 

 phenomenon, in the limits within which they have hitherto been ob- 

 served, it is sufficient to admit that the polar ice formerly extended 

 as far at the North Pole as it now extends at the South. Thus, 

 then, if the influence which has established the difference that exists at 

 present between the extent of the ice at the two poles be a periodical 

 influence, and if it describe one of those cycles of long revolution, 

 which astronomers have been able to determine, we can not only 

 conceive the possibility of a cold in our regions sufficiently intense to 

 produce all the phenomena which I have described, but may even be 

 able to determine its date and duration. I shall not reproduce here 

 my general theory of the periodical refrigeration of our globe, for 

 that would raise useless discussions in the field which the light of ob- 

 servation has not yet sufficiently illuminated ; I shall only cite one fact, 

 which tends to make us suppose that there really existed in the North 

 a covering of ice, whose southern limits in Europe, at a certain epoch, 

 reached about 50° N. Lat. I allude to that belt of blocks observed by 

 Russian geologists (see the letter from M. de Meyendorf to M. Elie 

 de Beaumont*), which extends across the centre of Russia, by N. 

 Nowogorod towards Pinsk, as far as the confines of Silesia. It seems 

 to me much more natural to regard this limit as an isopagetic line 

 (une ligne isopagetiquefj, than as the southern limit of a current 

 coming from the North, and charged with blocks ; and this so much 

 the more, because the phenomenon of the transport of the Scandi- 

 navian blocks extends not only into Russia and Germany, but reaches 

 the eastern coast of England. In attributing this effect to the action 

 of a current, it would thus be also necessary to imagine a fan- 



* Archiv fur Wissenchaftliche Kunde von Russland ; von Erman. Berlin, 1841. 



^ \(TOQ TTCty £TOCj that is to say, of equal ice ; in some sense the isotherme of the out- 

 line of the northern covering of ice ; but as the limits of this ancient ice do not coincide with 

 the isothermal lines, I have been obliged to propose a new name. 



