REVIEWS. 



351 



Rhone ; the reasons of their structure, to which M. Necker 

 has appHed the term torrent'ielle^' as evidenced in all 

 arenaceous deposits, and also in the disposition of coal mea- 

 sures^ which he considers as circumstances of no trivial 

 import as indicative of the origin of these different 

 rocks. 



Whilst speaking of the extraordinary depth of the lake of 

 Geneva, and discussing the reasons of this singular feature, 

 various novel ideas are introduced with reference to the 

 position of extensive lakes generally at the base of chains of 

 mountains of a certain geological age, by which our author 

 would imply that their existence and depth is attributable 

 to the sinking down of certain parts, as the natural conse- 

 quence of the up-heaving which produced the chains of 

 mountains themselves. 



A considerable portion of the work relates to the theory 

 of glacial action, in which the author differs greatly from 

 most of the geologists who have made this department their 

 particular study, and although the arguments are with espe- 

 cial reference to the more minute differences, yet in some 

 respects, they are of considerable importance ; let us instance 

 that portion which relates to the polished rocks so frequently 

 observed at high altitudes in the Alps, and the strise by 

 which they are marked. With reference to this subject, 

 M. Necker remarks, after speaking of the quantity of water 

 which exists beneath all glaciers, and consequently which 

 covers the subjacent rocks, that almost all rocks losing half 

 their weight by immersion, the pressure exercised by flinty 

 particles on them would be lessened by one half from what 

 they would effect, if their action took place under ordinary 

 atmospheric influences, and that consequently their agency 

 is comparatively trifling. Now, in this statement (which, if 

 recognized, would nullify the observations of many geolo- 



