Superficial Detritus of the Alps. 257 
Mont Blanc, to shew that, as each glacier is formed in a 
‘transverse upper depression, and is separated from its icy 
neighbour by an intervening ridge, so by their movement * 
such separate glaciers have always protruded their moraines 
across the adjacent longitudinal valleys into which they de- 
scended, and never united to form one grand stream of ice 
in the valley below. To prove this, it is affirmed that 
there are no traces of lateral moraines on the sides of the 
adjacent main valleys, whether on the side of the great ridge 
from whence the separate glaciers issued, or on the opposite 
side of such main valley, which must have been the case, if 
a large mass of glacier ice had ever descended it. On the 
contrary, examples of the transport of moraines and blocks 
across such main or longitudinal depressions are cited from 
the valley of Chamonix on the one flank, and from the 
Allée Blanche and Val Ferret on the other or south side of 
the chain of Mont Blanc. Another proof is seen in the an- 
cient moraine of the Glacier Neuva, the uppermost of the 
valley of the Drance; and a still stronger case is the great 
chaotic pile of protogine blocks accumulated on the Plan y 
Beuf, 5800 French feet above the sea, which have evidently 
been translated right across the present deep valley of the 
Drance from the opposite lofty glacier of Salenon. 
Having thus shewn that not even the upper longitudinal 
and flanking valleys around Mont Blanc were ever filled with 
general ice streams, the author has no difficulty in demon- 
strating that all the great trunk or lower valleys of the 
Arve, the Doire, and the Rhone, offer no vestiges of what he 
calls a true moraine ; since, although they contain occasional 
large erratic blocks, for the most partirregularly dispersed, 
all the other detritus is more or less water-worn, to great 
heights above their present bottoms. As Venetz and Char- 
pentier have attached great importance to the original sug- 
gestion of an old peasant of the Upper Vallais, that a great 
former glacier alone could have carried the erratic blocks to 
the sides of the lower valley of the Rhone; so, on the other 
hand, the author, if he had had any doubt himself, would have 
relied on the practised eye of his intelligent Chamonix guide, 
‘Auguste Balmat, who never recognised the remains of “ mo- 
VOL. XLVIII. NO. XCVI.—APRIL 1850. R 
