PROFESSOR LOUIS AGASSIZ. 613 



Alpine regions, were the result of the action of former glaciers de- 

 scending from the Alps and reaching even the upper portions of the 

 Jura. This theory Agassiz deemed improbable, till, having visited 

 Charpentier and investigated the phenomena, he not only became con- 

 vinced of the correctness of Charpentier's views, but deduced from 

 these and other phenomena a theory which, at the time (1837), was 

 startlingly novel. It was that, previous to the elevation of the Alps, 

 the globe experienced a very great reduction of temperature, and 

 that the appearance of those mountains found the surface of the 

 globe, from the north-pole to the Mediterranean Sea, covered with an 

 immense sheet of ice. An elevation of temperature, consequent upon 

 the upheaval of the Alps, caused this ice slowly to disappear, remain- 

 ing longest in the valleys, where it gradually retreated to its present 

 limits, leaving behind it, as a record, the peculiar phenomena which 

 have attracted the attention of so many observers. 



Of course a theory so novel at once raised a storm of opposition, 

 and it became necessary for Agassiz, if he would prove the correct- 

 ness of his views, to make the most careful and thorough investigations 

 on living glaciers. For this purpose Agassiz, in company with Desor 

 and several others, made visits in 1838 and 1839 to the glaciers of 

 Mont Blanc and the Bernese Oberland, and in 1840 established him- 

 self for the summer on the glacier of the Aar. That year he published 

 his " Etudes sur les Glaciers," giving the results of his investigations up 

 to that time. He also visited England, Scotland, and Ireland, and 

 studied the evidences of ice-action in those countries. 



But his labors were not finished. Doubting the sufficiency of the 

 theory of De Saussure — that the cause of the motion of the glacier 

 depends upon gravity — and inclined to accept the dilatation theory 

 of Schenchzer, it became necessary for him to examine with care the 

 structure, form, distribution, and rate of motion of the glacier. Thus 

 it was that, in 1841, he began a second series of observations for the 

 purpose of determining these points. He chose, for the theatre of his 

 investigations, the glacier of the Aar, which, by its extent and acces- 

 sibility, promised the most favorable results. In 1845 he had com- 

 pleted his work, and in 1847 appeared his "Systeme Glaciaire," which 

 embodied the final results of his researches upon the structure of 

 glaciers, and their effects upon the soil. The results at which he 

 arrived may be summarized as follows : The glacier is a mass of ice 

 reclining on the side of a mountain-ridge, or inclosed in a mountain- 

 valley ; it is always descending, and, while wasting away from heat at 

 its lower extremity, is continually augmented at its source. The pri- 

 mary material of glacier-ice is the snow which falls in the high regions of 

 the mountain. The yearly addition of snow in the higher cold regions 

 gradually forces the snow down the valley ; here, subject to alternate 

 thawing and freezing, it undergoes a second crystallization into what 

 is called n&ve snoio, and still farther down, under increased pressure, be- 



