INTRODUCTION. 



9S 



NOTE E. 



I HAVE already alluded to the explanation, given by Sir John Herschel, of the 

 process by which continental areas may be elevated from the accumulation of de- 

 posits upon the ocean bed. I have seen this explanation only as published in the 

 appendix to Babbage's Ninth Bridgwater Treatise, as an extract of a letter from 

 this philosopher to Sir Charles Lyell. Since this and another letter to Lyell, and 

 one to Sir R. I. Murchison, contain many suggestions which seem to me as offering 

 support to the views I have advanced, I have made some extracts which follow : 

 After discussing the question of the rise of the isothermal surfaces beneath the 

 earth's crust from the deposition of new matter on the bed of the ocean, a view 

 which appears to have originated in the minds of Babbage and Herschel quite 

 independently of any knowledge of each other's conclusions, he goes on to speak 

 as follows (alluding to Lyell's Principles of Geology) : 



" According to the general tenor of yonr book, we may conclude that the greatest transfer 

 of material to the bottom of the ocean is produced at the coast line by the action of the sea, 

 and that the quantity carried down by rivers from the surface of continents is comparatively 

 trifling. WTiile, therefore, the greatest local accumulation of pressure is in the central area 

 of deep teas, the greatest local relief takes place along the abraded coast lines. Here, then, 

 in this view, should occur the chief volcanic vents. If the view I have taken of the motion- 

 less state of the interior of the earth be correct, there appears no reason why any such influx 

 of heat should take place under an existing continent (say Scandinavia) as to heat incum- 

 bent rocks (whose bases retain their level) 5 or 600° Fahrenheit for many miles in thickness 

 ( Princ. of Geology, Vol. ii, p. 384 : 4th edition). Laplace's idea of the elevation of sur- 

 faces due to columnar expansion (which you attribute, in a note, to Babbage), is, in this 

 view, inadequate to explain the rise of Scandinavia or of the Andes, &e. But, in the varia- 

 tion of local pressure due to the transfer of matter by the sea, on the bed of an ocean im- 

 perfectly and unequally supported, it seems to me an ac^equate cause may be found. Let A 

 be Scandinavia, B the adjacent ocean 

 (the North Sea), C a vast deposite newly 

 laid on the original bed of the ocean, 

 E E E a semifluid or mixed mass on 

 which D D D reposes. What will be the 

 effect of the enormous weight thus added 

 to the bed D D D ( rock being heavier 

 than sea ) ? Of course, to depress D 

 under it, and to force it down into the 

 yielding mass E, a portion of which will be driven laterally under the continent A and up- 

 heave it. Lay a weight on a surface of soft clay : you depress it below, and raise it around 

 the weight. If the surface of the clay be dry and hard, it will crack in the change of figure." 



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