INTRODUCTION. 89* 



thickness of accumulated deposits have any influence in strengthening the crust of 

 the earth, these lines should be the stronger ones; while the really weaker lines 

 would lie in the great plains where the strata are thinner, and as a consequence 

 we might suppose weaker. 



We find the most extensive areas where the stratified deposits are comparatively 

 very thin, to be those which are wholly free from disruptions, fractures, or any 

 disturbances whatever. It has been long ago said by Lyell, that the " ordinary 

 repose of the surface of our planet argues a wonderful inertness in the interior;" 

 and if, as Sir John Herschel conceives, " everything in the interior is motionless," 

 we must look for external influences to provoke the interior manifestations. These 

 external influences are mainly the abrasion and removal, and the redepositing of 

 sedimentary matter; and it seems to me extremely doubtful if any disruption, or 

 other manifestatiou of the internal agencies can occur, except along lines or upon 

 areas where great accumulations have taken place*. 



IVOTE B.— (See Pages 66 & 67.) 



Whatever may be the influence of the accumulation of matter upon the ocean bed 

 in affecting the isothermal surfaces or strata of the crust beneath, and thus producing 

 an elevation of the temperature and a consequent expansion in the recently de- 

 posited matter, according to the views of Babbage, Herschel and others, I cannot 

 suppose that it will materially affect the conclusions I have advanced. Indeed I 

 think we have too many facts pointing to the existence of shallow seas during the 

 deposition of sediments to doubt it, while the great accumulations could only be 

 made by a gradual or periodical sinking of the sea bottom. The deposition would 

 probably be so rapid as to depress the yielding crust much more rapidly than the 

 expansion from the rise of the isothermal surfaces. Moreover, as the deposition goes 

 on and the isothermal surfaces rise, the beds beneath may be gradually softened by 

 the increasing heat, and become the more readily yielding; while the weight of the 

 accumulating mass above remains the same, or is slowly increased. 



• The great plateaux of undisturbed palaeozoic strata in America, Northeastern Europe and else- 

 where, offer good examples in support of the views I hare advanced. 



