672 
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 he judges that such was the case, because the “aiguilles” 
of Mont Blane have been lowered very considerably in our own 
times. Arguing that great blocks are never found at the foot of 
mountain chains which have not permanent glaciers, of what De 
Saussure called the “first class,” he 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 those 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. Neeser, that if he assumes that all 
great erratic blocks are to be referred to some neighbouring chain, 
now the seat of glaciers, he forgets the cases in Scotland and England, 
and indeed many others, far removed from mountain ranges, and 
which must be classed, as I shall presently show, with submarine 
deposits. Indeed by far the widest spread of erratic blocks with 
which we are acquainted, extending over the plains of Germany and 
Russia, must have taken place (as I believe at least) when those flat 
regions were beneath the sea, for recent observations have shown, 
that the blocks constitute the uppermost or last surface deposit in 
tracts which exhibit, here and there, proofs of having been an ancient 
bottom of a sea. But without extending his theory to other parts 
of the world, it does not appear to me, even when confined to the 
Alps, that M. Necker explains satisfactorily how the granite blocks 
of Mont Blanc should lie upon the Jura, by any reference to sub- 
aérial debacle; for if we are to imagine the deep hollow of the lake 
of Geneva, filled up with gravel, sand and mud, and forming an in- 
clined talus from the centre to the flanks of the chain, the subse- 
quent scooping out of this enormous mass of materials involves an 
intensity of degradation as difficult to believe in as the former extreme 
elimate of Agassiz, by which thousands of feet of snow and ice are 
supposed to have occupied the same deep valley. I ought not to 
omit to state that one of the chief elements introduced by Agassiz 
into this question, the polished and striated surfaces of the rocks, 
has not yet been alluded to by this author, but will be treated of in 
his second volume. 
In the mean time, however he may fail to account satisfactorily 
