Superficial Detritus of the Alps. 259 
Fully admitting that the stones and sand of the moraines 
of modern glaciers scratch, groove, and polish rocks, Sir 
Roderick Murchison still adheres to the idea he has long en- 
tertained from surveys in Northern Europe,* that other 
agents more or less subaqueous, including icebergs and heavy 
masses of drift, have produced precisely similar results. 
He cites examples in the Alps, where, perfectly water-worn 
or rounded gravel being removed, the subjacent rocks are 
found to be striated in the directions in which such gravel 
has been moved; and he quotes a case in the gorge of the 
Tamina, above the Baths of Pfeffers, where this ancient stri- 
ation, undistinguishable from that caused by existing glaciers, 
has, by a very recent slide of a heavy mass of gravel from 
the upper slope of the same rock, been crossed by fresh sco- 
rings and striz, transverse to those of former date, from which 
the markings made in the preceding year only differ in being 
less deeply engraved. He also adverts to the choking up of 
some valleys, particularly of the Vorder or Upper Rhine, be- 
low Dissentis, by fracture, in si/w, of mountains of limestone, 
which constitute masses of enormous thickness, made up of 
innumerable small fragments, all of which have been heaped 
together since the dispersion of the erractic blocks ; and he 
further indicates the effects of certain great slides or sub- 
sidences within the historic era. 
In considering the distribution of the erratic detritus of 
the Rhone, the author having denied that it can ever have 
been carried down the chief valley to the Lake of Geneva in 
_asolid glacier, he still more insists on the incredibility of 
such a vast body of ice having issued from that one narrow 
valley, as to have spread out over all the low country of the 
feel most entirely convinced that floating ice and glaciers produce effects so 
; similar, that at present there is, in many cases, no means of distinguishing 
_ which formerly was the agent in scoring and polishing rocks. This difficulty 
__ of distinguishing the two actions struck me much in the lower parts of the Welsh 
valleys.” 
* See Silurian System, pp. 509 to 547 ; Russia in Burope and the Ural Moun- 
tains, vol. i., pp. 507 to 559; Presidential Discourses, Proc. Geol. Soc., Lond., 
ol, iii., p. 671, and vol. iy., p. 93 ; Journ. of Geol. Soc., Lond., vol. ii., p. 349; 
_ and Trans. R. Geol. Soc., Cornwall, vol. vi. 
