272 Reviews— Tyndall and Ramsay on Erosion. 
valley. This is remarkably the case on the Italian side of the 
Spliigen Pass ; and we are surprised that Professor Tyndall has 
not alluded to it. We can assure him that it fully supports his 
argument. 
After pointing out that, in the elevation necessary to bring the 
Alps into their present state, the area of the fissures produced by 
the cracking of the rocks would be very much smaller than the areas 
of the existing valleys, and that the character of the valleys is not 
such as would be produced by elevation and cracking, Professor 
Tyndall proceeds to consider the mechanical effect of glaciers. That 
the principal crushing and grinding effect of a glacier must be under 
the middle part, where the motion is most rapid, is certain: that the 
walls of a valley are really torn by a glacier passing down between 
them, and that obstacles to downward progress, when it can be 
traced, are rapidly and effectually removed, are matters of observa- 
tion; and these points are sometimes well seen in the valleys from 
which the smaller glaciers retire during summer. Thus in the 
valley near Engelberg, towards the Surenen Pass, we have noticed 
these results; and indeed every one who has been among the ice in 
the higher valleys is familiar with numerous such instances. That 
in former times, during the Glacial Period, the ice was more abun- 
dant and more efficacious is only another way of saying that there 
was a Glacial Period. The Erosion-theory evokes, therefore, as 
Professor Tyndall observes, nothing but true and known causes ; 
while the Fracture-theory cannot of itself explain the phenomena. 
Professor Tyndall believes that the fissures formed during elevation 
were insufficient to determine the conformation of the Alps; but 
this is a conclusion concerning which we feel inclined to think that 
much remains to be said. 
Professor Ramsay, in the article bearing his name, replies to Sir 
R. Murchison’s recent attack on the Erosion-theory. Sir Roderick, 
as our readers are aware, and as is well expressed in the article 
before us, believes that ‘mountain-valleys lie in lines of curvature, 
dislocation, and fracture; and that the mountains on each side of 
them are mountains far less because of denudation than by reason of 
operations of fracture and dislocation.’ 
Professor Ramsay asks for the proof of such faults and dislocations 
in the Alps. He believes that, when accurate geological sections 
(on the true scale) shall have been made through Switzerland and 
the adjoining mountain-tracts, there will be ample proof of enormous 
denudation previous to the conformation of the existing valleys, and 
that these have necessarily been formed long since the latest important 
disturbances of the strata took place. 
Referring to the argument so much insisted on, that the opinion 
of ‘the vast majority of practical geologists’ is worthy of some 
respect, our author refers to the writings of Hutton and Playfair, 
quoting the former to show that the modern view of the overwhelm- 
ing importance of water-action is really a very old one, and the 
latter to the effect that ‘the sharp peaks of the granite mountains 
but mark so many epochs in the progress of decay,’ and that ‘the 
