240 Professor Agassiz on the Glacier Theory. 



phenomenon of stratified fossiliferous deposits and of parallel 

 terraces, such as we find so frequently in Scotland. 

 [ It was in Scotland that I acquired precision in my ideas re- 

 garding ancient glaciers. The existence in that country of so 

 considerable a network of these traces, enabled me to appre- 

 ciate better the geological mechanism of glaciers and the im- 

 portance of many facts of detail observed in the neighbour- 

 hood of those which now exist. There, also, I was able to ap- 

 preciate the influence exercised on these phenomena by the 

 vicinity of the sea, and to distinguish the effects due solely to 

 the waters of the sea from those where the ocean and glaciers 

 were in contact, and from those produced where the glaciers 

 never reached the sea. Who would now deny that glaciers 

 formerly possessed in many localities an infinitely greater ex- 

 tension than at present ? Who would reject the idea that the 

 cause of this cold has been general, and attribute to local causes 

 effects so diffused over the surface of the globe \ And if these 

 conclusions must be admitted, who does not perceive that phy- 

 sical theories must undergo some modifications before they 

 can be made to embrace the whole phenomenon which 1 have 

 described ? It is thus that the study of facts in detail always 

 reacts on general ideas ; while, in their turn, theories, in order 

 to be supported, force their partisans to the investigation of nev/ 

 facts. The activity of mind that is engendered by the contests 

 to which researches of this kind always give rise, is probably 

 the greatest enjoyment afforded us in this world. 



II. Researches on Existing Glaciers. 



The chief question in the glacial theory is undoubtedly that 

 of the motion of glaciers ; it is the keystone of the arch of the 

 edifice, for it includes at the same time the solution of the 

 phenomena of the present time, and of those which occurred 

 before our epoch. It is well known that opinions have hither- 

 to been divided as to the progression of glaciers, and that many 

 geologists, refusing to admit the theory of dilatation, still de- 

 fend the opinion of Griiner and of Saussure, which maintains 

 that a glacier slides along its bed. 



In my Etudes siir lea GlaclerSy I have entered fully into the 



