THE ICE AGE AND ITS WORK. 279 



down tlie Rhone Valley as far as the Jura, and there deposited the 

 erratic blocks which had so f)iizzled the diluvialists to explain. 



Other writers soon followed the clue thus given. In 1835, Charpen- 

 tier, after a close study of the erratic blocks and of their sources, 

 adopted the views of Venetz. Agassiz followed, and by his strenuous 

 advocacy did much to spread correct views as to the former extension 

 of the Alpine glaciers, and their capability of explaining the numerous 

 superficial phenomena which in all northern countries had been thought 

 to att'ord proofs of enoniKuis floods and of the submergence of a large 

 part of Europe under a deep sea. lie has- therefore gained the repu- 

 tation of being the originator of the modern school of giacialists, which 

 undoubtedly owes much to his energy, research, and powers of exposi- 

 tion, though all the more important facts, as well as the logical con- 

 clusions to be drawn from them, had been pointed out by previous 

 writers. 



Before iiroceeding further, it will be well to give a brief outline of the 

 lihenomeua which led to the conclusion that glaciers have formerly 

 existed m districts and countries where even perpetual snow on the 

 mountain tops is now unknown. These may be briefly classed as (1) 

 moraines and drifts; (2) rounded, smoothed, or planed rocks; (3) striae, 

 grooves, and furrows on rock-surfaces; (4) erratics and perched blocks. 



(1) Moraines are those heapsorridgesof rock and other debris which 

 are deposited on the surface of a glacier from the precipices or moun- 

 tain slopes which border it, and which form what are termed lateral 

 and medial moraines while upon it, and terminal moraines when, being 

 gradually discharged at its end, either from above or from beneath it, 

 they form great heaps of rock and gravel corresponding in outline and 

 extent to that of the terminal ice-cliff. Such moraines can be seen on 

 and near all existing glaciers, and their mode of formation and char- 

 acteristics are perfectly well known. - 



(2) Smoothed and rounded rocks, called in Switzerland " roches 

 moutonnees," from their supposed resemblance at a distance to sheep 

 lying down, are perhaps the most general of all the indications of glacial 

 action. Every glacier carries with it, imbedded in its under surface, 

 numbers of rocks and stones, which, during the slow but unceasing 

 motion over its bed, crush and grind down all rocky projections, pro- 

 ducing in the end gently rounded or almost flat surfaces even on the 

 hardest and toughest rocks. In many of the valleys of Wales, the Lake 

 District, and Scotland every exposed rock has accpiired this character- 

 istic outline, and the same feature can he traced on all the rocky slopes 

 and often on the summits of the lesser heights; and the explanation of 

 how these forms have been produced is not a theory only, but has been 

 observed in actual operation in the accessible portions of many glaciers. 

 Rocks and stones are to be seen embedded in the ice and actually 

 scratching, grooving, and grinding the rock beneath in their slow but 

 irresistible onward motion. - - - 



