260 PROGRESS OF SCIENCE IN THE CENTURY. 



Study of Glaciers. The study of glacial action 

 may fairly date from H. B. Saussure's famous 

 Travels in the Alps, in which glaciers and moraines 

 were described with detailed accuracy. Saussure was 

 followed by Hugi, an enthusiastic mountaineer, who 

 explored the upper reaches and was the first liter- 

 ally to sojourn on the slowly moving ice-sheets. An 

 important step was taken by Venetz, an engineer, 

 who, from 1821 onwards, sought to prove from the 

 distribution of moraines the enormous prehistoric 

 development of glaciers, not only in Switzerland, but 

 in North Europe. Venetz converted J. v. Charpen- 

 tier, who, in turn, strengthened his friend's argument 

 with evidence drawn from the wide occurrence 

 of erratic blocks which only ice could have car- 

 ried. 



Agassiz. Louis Agassiz soon caught the enthu- 

 siasm, and began along with Charpentier and the 

 botanist Schimper a prolonged series of excursions 

 and observations which led him to the conception 

 of a Great Ice Age, which was developed in a book 

 published in 1840. From his study of past floras 

 and faunas Schimper had been led to the idea of 

 alternating periods of desolation and rejuvenation 

 as a Great Ice Age. 



Agassiz was stronger in his description of glacial 

 phenomena and in his recognition of the previously 

 wide extension of glaciers (aa proved by erratic 

 blocks, striated surfaces, etc.) than in his Ice Age 

 theory. But let us try to summarise his conclu- 

 sions. Before the elevation of the Alps, an immense 

 ice-sheet covered most of the northern hemisphere; 

 the Alps arose, and the debris of broken ice-sheet 

 and shattered strata fell on the adjacent glaciers, which 

 bore off their heavy burden, grinding the movable 



