Notice of Prof . Forbes 1 s Travels in the Alps. 173 



many new and valuable engineering observations taken with accurate 

 instruments, and often made in painful or dangerous circumstances, 

 among the eternal snows and treacherous ice-cliffs and glaciers of the 

 Alps! It abounds with daring and hazardous adventures, contains notices 

 of occasional catastrophes that have befallen less fortunate explorers ; 

 presents interesting discoveries, with new deductions, and is clothed 

 in a style and diction entirely in keeping with the beauty and gran- 

 deur of the subject.^ If a literary reader would sometimes tire amidst 

 the almost endless details, on Alpine snows, crevasses and glaciers, 

 he would be relieved, at short intervals, by unrivalled beauty of descrip- 

 tion and sublime sketches of those scenes which are forever arrayed in 

 a wild and terrible grandeur. We have perused the work with intense 

 pleasure and large instruction, and with a conviction, if possible increas- 

 ed at every step, of the great energy of the action of glaciers in furrow- 

 ing and scratching and polishing those rocks upon which they repose, 

 if repose it can be called where there is no rest, since the glaciers are 

 always advancing in immense fields and rivers of ice upon the country 

 below ; and were it not, that the melting at the lower end of the ice- 

 cliffs prescribes limits to their extension, it is not easy to see why they 

 would not eventually usurp dominion over a large portion not only of 

 the polar but of the temperate zones of the earth, which they are sup- 

 posed by Agassiz to have formerly covered. 



Prof. Forbes accords with all other writers on the subject that " the 

 snow which falls on the summit of the Alps, becomes converted into ice 

 by successive thaws and congelations," but the explorers who have pub- 

 lished their views have not been agreed as to the immediate cause of 

 the descent of these frozen masses down the vallies and towards the 

 plains. Dilatation by the freezing of water, and gravitation, include the 

 principal theories. 



The author denies that the descent of the ice is due to dilatation, 

 while this cause, as he believes, contributes to swell the volume of the 

 ice upward or at right angles to the bed of rock on which it lies. 

 Gravitation, as he avers, could never move downward a rigid inflexible 

 field of ice upon a rocky and uneven bottom, and often confined between 

 projecting buttresses, where the approximation of mountain cliffs nar- 

 rows the space into a gorge or strait, in the manner in which rivers are 

 pent up by opposing walls. 



The declivity of the Mer de Glace averages only 9°, and in many parts 

 hardly equals that of many hills over which loads are drawn by ani- 

 mals ; in many cases it does not exceed 5° — less than the slope of the 

 great Simplon, which is a road for artillery, and often it falls far short of 

 that amount ; this fact renders it highly improbable, not to say impossible, 

 that a firm field of ice should slide down such a gentle declivity, espe- 



