The Glacial Tlieory. 579 



As propounded by Agassiz, the glacial theory, even in its appli- 

 cation to the Alps, has met with an opponent in the person of Pro- 

 fessor Necker de Saussure. In the first volume of a work which he 

 is now publishing, M. Necker treats, in great detail, the whole sub- 

 ject of superficial detritus connected with the northern and western 

 watershed of the Alps, and gives us the fruits of many years of ob- 

 servation. Adding very considerably to the list of phaenomena of 

 transported materials collected by M. A. de Luc, he takes his own 

 illustrious ancestor, De Saussure, as his model, and following in the 

 track of the historian of the Alps, he endeavours to enlarge and 

 improve upon that great observer's suggestions. Pointing out the di- 

 stinctions between two classes of detritus, viz. one of high antiquity 

 and another of modern date, M. Necker contends that the enormous 

 masses of the ancient drift or diluvial detritus have a direct con- 

 nexion with the actual configuration of the surface, because the 

 cAi'e/'part of them has been derived from the centre of the chain, 

 the flanking and lower mountains, and even the strata on which it 

 rests, having contributed comparatively little to the great advancing 

 body. Examining the high valleys about Chamouni and tlie foot 

 of Mont Blanc, and finding massive walls from 300 to near 600 

 feet in height, composed of this ancient diluvium in its coarsest 

 form, near the extremities of certain glaciers, he concludes that 

 they were once the moraines of glaciers which melted away and 

 retired from them. He then goes on to suppose that when the re- 

 cession of the glaciers took place (an effect which he refers to the 

 same cause as De Saussure) such transversal moraines formed dykes 

 standing out at some distance from the mountain and barred-up 

 lakes formed by the melting of the snow and ice. These lakes, at 

 length swollen to excess, are supposed to have burst through the 

 moraine barrier, and to have drifted the materials of which it was com- 

 posed into the lower countries. M. Necker believes that when these 

 ancient glaciers existed, the Alps were considerably higher than at 

 present, and lie judges that such was the case, because the "aiguilles" 

 of Mont Blanc have been lowered very considerably in our own 

 times. Arguing that great blocks are never found at tlie foot of 

 mountain chains which have not permanent glaciers, of what De 

 Saussure called the " first class," lie cites many negative examples, 

 and brings forward the Pyrenees, where no true erratic blocks are 

 seen, as a proof that the minor or second class glaciers, which there 

 occur, never advanced sufficiently far to dam up water-courses, and 

 thus to form tiiose great lakes, to the letting off of which and to the 

 destruction of vast moraines, he attributes the presence of large 

 boulders in the Alps. 



I must, however, remind M. Necker, that if Jie assumes that all 

 great erratic blocks arc to be referred to some neighhourinrj chain, 

 now the seat of glaciers, he forgets the cases in Scotland and England, 

 and indeed many others, far removed from mountain ranges, and 

 wiiioli must be classed, as I shall presently show, witii submarine 

 deposits. Indeed l)y far the widest spread of erratic blocks with 

 which we arc acquainted, extending over tlie plains of Germany and 



