A Period in the History of our Planet. 19 



imprinted are their characteristic marks, that the roaring 

 breakers have not even yet been able to erase them. 



On the other hand, the ice has imprinted upon all the 

 mountain tops of Great Britain, which in Ben Nevis rise more 

 than 4000 feet above the level of the sea, the stamp which 

 attests its former presence ; and there can be no doubt that 

 its colossal masses were piled up above the highest summits 

 of these mountains. 



In like manner, on the high ridges and peaks of the Alps, 

 the thickness of the mass of ice can be directly measured ; at 

 least we are able to determine to what absolute height the 

 solid glacier ice extended. How high the Firn^ and the snow 

 which perhaps rested upon it, may have reached, we can now 

 have no exact knowledge, as it is only the solid ice that 

 scratches the traces of its presence upon the rocks, whilst 

 the light snow and the granular incoherent Firn leave no 

 mark of their existence. By various barometrical measure- 

 ments I have found that in our Alps the limits of the solid 

 ice on the sides of valleys, the bottom of which is from 2000 

 to 3000 feet in absolute height, and which are now entirely 

 free from glaciers, reach to a height of more than 8000 feet 

 above the level of the sea. 



What a huge mass, transcending our utmost conceptions ! 

 Admitting, what in fact must be assumed, that the covering 

 followed in its extent the different inequalities of the surface, 

 that, consequently, the circumstances of traces of ice being 

 found in the Alps to such a height affords no proof of an every 

 where similar absolute height of the icy surface ; that it affords 



recent scientific accounts respecting the glaciers and ice-fields of the polar regions, 

 that the masses of ice which are so formidable in the high northern latitudes as 

 floating ice-bergs, are fragments of glaciers, which, stretching out from the solid 

 land into the sea, are undermined by the waves and deprived of their basis, until 

 at length gravity overpowers their coherence with the masses which rest upon the 

 land, and the block falls into the sea. It results from a consideration of this phe- 

 nomenon, as well as from direct observation, that, as far as the sea reaches, the 

 glacier ice is dissolved, and, consequently, it does not come in contact with the 

 bottom of the sea. 



The north sea of the glacial period had therefore eitlier a much lower level than 

 at present, or else, as seems to be almost proved by a consideration of the whole 

 phenomena, its basin was filled to the bottom with solid ice. 



