526 Reinews — Ramsay^ s Physical Geology. 



follow the strike of the beds, coupled with the fact that the strike is 

 generally ignored by littoral marine action, naturally led to the 

 belief that such escarpments were formed by an agency which is 

 either free to run along, or only capable of running along, the soft 

 outcropping strata. It was likewise clearly perceived that littoral 

 marine action cannot originate narrow A'alleys which ramify from 

 lower to higher levels. It is not, therefore, surprising that the 

 school of geologists led by Professor Eamsay should have found 

 themselves driven to the agency of " rain and rivers " as the only 

 resource left, more especially as "the inimitable Playfair" long 

 before, and Greenwood and Jukes at a later period, had ably applied 

 the rain-and-river or subaerial theory to the explanation of longi- 

 tudinal valleys and transverse gorges. 



It is very obvious that the subaerial theory has been partly founded 

 on the belief that no agency excepting rain and rivers will explain 

 the phenomena above specified. This theory takes for granted that 

 there is " no wasting action '^' under the surface of the sea (see p. 69 

 of the work under review). But as the spectroscope proved the 

 existence of gaseous nebulse after the idea had been rejected on 

 astronomical grounds, so discoveries connected with hydrodynamical 

 science are now beginning to show that denudation must take place 

 not only at small depths beneath the surface, but at the bottom of 

 deep seas. It is impossible for cold, dense under-currents, such as 

 those brought to light by deep-sea dredgings, to impinge on the 

 sea-bottom, without exerting a wasting influence ; and as none of 

 these currents are probably violent enough to wear away soft and 

 hard parts alike, or to ignore the strike of submarine strata, we may 

 reasonably conclude that they are capable of doing much of what has 

 been theoretically attributed to the diffused action of rain, and a 

 part of what has been referred to rivers. But admitting that many 

 broad excavations, troughs, and passes, were slowly wasted out, and 

 escarpments left, before the land rose above the sea, we can no 

 longer dispute that rain-torrents, rivers, and ice have since then 

 modified the surface of the land to a very great extent. 



In the work before us the enormous extent of the denudation to 

 which Great Britain has been subjected is clearly proved by sections 

 and arguments, and this part of the work is especiall}"^ valuable. 

 The cause of the denudation resolves itself into the comparatively 

 unimportant question of fresh or salt water. Though many will not 

 agree with Professor Ramsay in his preference for fresh water, all 

 will admire his beautiful explanation of the manner in which the 

 denudation has been achieved ; and in connexion with this subject 

 his work contains some very important original contributions to 

 geological science. 



We have said so much on denudation, that we have little space 

 left to notice the work in detail. The first four chapters are on the 

 Classification of Eocks, the Ages and Successive Deposition of 

 Stratified Formations; Synclinal and Anticlinal Curves; Denudations 

 by Mechanical and Chemical Action ; Metamorphism, Shrinkage, and 

 Disturbance of the Earth's Crust, etc. These chapters include the 



