230 Professor Agassiz on the Glacial Theory, 



not commanded by numerous mountain peaks, then few or no 

 angular blocks would fall on its surface, but the rounded 

 blocks underneath would not the less be present. If we ima- 

 gine that, in such a case, particular circumstances should also 

 occur to cause the melting of the ice, there would then be 

 found at the bottom an irregular deposit of rounded blocks, 

 imbedded in the more comminuted materials, along with a 

 few angular blocks above — in short, to the very letter, a sort 

 of till. In this case, again, the melting of the ice would give 

 rise to currents ; and the more considerable these currents, 

 the more they would contribute to operate farther on the ma- 

 terials already acted on by the glaciers, whether by conve}^- 

 ing to a distance the lighter portions, and depositing them in 

 regular stratification, or by penetrating them more or less, 

 and giving them a false appearance of stratification. We ac- 

 tually observe something of a similar kind, on a small scale, 

 in the oscillations that occur at the extremity of glaciers 

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

 the extremity of the lower glacier of the Aar in the Grimsel- 

 grund ; and, among the localities where glaciers no longer 

 exist, I may cite the lower extremity of Loch Treig, and the 

 neighbourhood of Muckairn, between Loch Awe and Loch 

 P^tive. 



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

 erratic phenomenon, in the limits within which they have hi- 

 therto been observed, it is sufficient to admit that the polar 

 ice formerly extended as far at the North Pole as it now ex- 

 tends at the South. Thus, then, if the influence which has 

 established the diff^erence 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 enabled 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 discus- 

 sions in a field which the light of observation has not yet suf- 

 ficiently illuminated ; I shall only cite one fact, wliich tends 



