§ 32. ICEBERGS AND GLACIERS. 73 



heaps of boulders. The movement of the glacier from the 

 mountain top, arises from the softened state of the layer 

 of ice in contact with the surface of the earth on which it 

 rests ; for the beautiful experiments of Professor Forbes 

 have shown that ice moves upon the principle of a tenacious 

 or viscous fluid ; that is, by gravitation on an inclined 

 surface. The rocks forming the bases of the glaciers, 

 and the sides of the valleys they have traversed, are more 

 or less polished and grooved, from the passage of angular 

 masses of rock when impacted in the moving ice : the 

 grooves being in the direction of the movement of the 

 glacier.* 



From careful observations on these appearances, M. 

 Agassiz has established characters by which, in countries 

 where the hills are at the present time far below the snow 

 line, evidence of former glaciers of great extent has been 

 obtained. Many indications of ancient glaciers are supposed 

 to occur in England and Scotland ; and the accumulations 

 of drifted materials, containing large angular blocks, and 

 disposed in long banks and ridges, and the grooves and 

 scratches on the surface of the rocks forming the sides of 

 valleys and slopes of hills, which lead off from these sup- 

 posed moraines, are regarded by some geologists as un- 

 equivocal proofs of a great extent of glaciers in these 

 islands at a comparatively recent period : and the drift, 

 boulders, and superficial alluvial debris, are attributed, in 

 a great measure, to the agency of either icebergs or glaciers. 

 But the sweeping conclusion of M. Agassiz and others, 

 that the whole of Europe was once covered with ice, should 

 be received with much hesitation ; and it is to be regretted 

 that the term " glacial period" has been admitted into 

 geological nomenclature. 



* See "Etudes sur les Glaciers/' par M. Agassiz; Neuchatel, 1840; 

 and the Works and Memoirs of Prof. Forbes (in the Philos. Trans.), 

 on the same subject. 



