PROFESSOR LOUIS AGASSIZ. 615 



The sides as well as the bottom of the glacier are studded with 

 bowlders, pebbles, and sand, forming a gigantic rasp. As the glacier 

 moves forward, this rasp grinds, furrows, and polishes the rocks over 

 which it moves, the furrows trending in the direction in which the 

 glacier moves. These furrows and "polished surfaces, which are often 

 observed on rocks remote from any living glaciers, are the record of 

 the former existence of glaciers in such places. When the ground is 

 uneven, the eminences being small, and the hollows too deep and 

 wide to be bridged over by the glacier, the ice-rasp rounds and pol- 

 ishes these knolls, forming those rounded elevations which have re- 

 ceived the name of roches moutonnees. In consequence of the rocky 

 walls above the sides of the glacier becoming warmed by the sun, the 

 ice is melted near them, and hence the glacier becomes convex. Into 

 these troughs the debris from the walls fall and form long lines of bowld- 

 ers, pebbles, and sand, which are called lateral moraines. When two 

 glaciers flow together, the two lateral moraines on the adjoining sides of 

 each unite and form what is called a medial moraine. A third form, 

 the terminal moraine, is the accumulation of sand and rocks which 

 the glacier pushes before in its progress down the valley. In conse- 

 quence of the increased rate of progression of the centre of the gla- 

 cier, these terminal moraines assume a semicircular form, which, when 

 the glacier retreats, consequent upon an excess of liquefaction over the 

 snow-supply, leaves a crescentic wall across the valley, usually cut in 

 two by the river flowing from the glacier. The erratic blocks which 

 are found over most of the globe, accompanying scratched and pol- 

 ished rock-surfaces, are simply the bowlders of the surface of the glacier 

 left on or near the spot where they stood when the glacier disappears. 



In the fall of 1846 Agassiz sailed for the United States, on a mis- 

 sion from the Prussian Government. The warm reception which 

 greeted him here, and especially the rare field for scientific research 

 which this country afforded, determined him, the next year, to make 

 America permanently his home. The professorship of Natural His- 

 tory in the Lawrence Scientific School at Harvard College being 

 offered him that same year, he accepted it, and held the position till 

 his death, with the exception of two years when he occupied the chair 

 of Natural History in the University of South Carolina, at Charleston. 

 In 1848, in connection with H. E. Strickland, he began the publication 

 of a " Bibliographia ZoologiaB et Geologic." This work, which com- 

 prises a list of all the periodicals devoted to zoology and geology, and 

 an alphabetical list of authors and their works in the same departments, 

 was completed in four volumes, the fourth being published in 1854. 



Agassiz's studies on the glaciers of Switzerland led him to expect 

 to find in the United States many traces of former ice-action. Nor 

 was he disappointed. He explored the country from the Atlantic to 

 the Rocky Mountains, from the great lakes to the Gulf of Mexico, and 

 everywhere, north of the thirty-fifth parallel of latitude, found evi- 



