GENERAL CONSIDERATIONS. 131 



11 sediment to any part of the earth's crust must raise the temperature of 

 " the portion of the crust it covers" 1 ; and later, that Captain Dutton, 

 of New Zealand, accounted for the anticlinal of the Weald through the 

 rise of the isogeotherms caused by sedimentation. 2 Now, it is easy 

 to see that, if a trough-like sea, of a certain depth, becomes gradually 

 shallower and shallower as sediment is poured into it, there will be 

 a rise in temperature of what was once the bottom of that sea ; 

 but all cases of great sedimentation cannot be considered in this 

 simple form. No one will suppose that the accumulation of 20,000 or 

 30,000 feet of strata took place in a sea which was once of that depth 

 and which gradually became silted up. Great sedimentation of this 

 kind can only take place by concomitant sinking of the sea bottom ; 

 so that the rise of the isogeotherms being interpreted means merely 

 the sinking of the floor on which the deposits were laid down. At 

 page 266 the author recognises this when he says "the accumulation 

 " of a great thickness and extent of sedimentary deposits pre-supposes 

 " subsidence of large areas — regional subsidence as it maybe called." 

 If therefore great sedimentation is the cause of mountain-building, 

 since subsidence is the cause of sedimentation, or rather its necessary 

 accompaniment, then great depressions of the earth's crust must be 

 looked upon as the ultimate condition or accompaniment of mountain- 

 building; that is, a subsidence of the earth's crust is either the cause 

 or accompaniment of a rising in the same locality, which is absurd 

 As well might one say that the defeat of an army in one battle 

 is the cause of its victory in the next ; or that the greater the piles of 

 dead in the one the greater the triumph that will follow. 



Again, the author, in endeavouring to account for the subsidence, 

 continues (page 270) — u If we assume, as we have reason to do, that 

 " the heated interior of the earth below the crust, solid only by pressure, 

 "is subject in large masses to change of volume by change of tempera- 

 u ture, caused by re-combination [chemical combination ?] of matter 

 "taking place from time to time, many difficulties can be explained. 



1 Page 89, 

 3 Page 90. 



12 ( 189 ) 



