r 



240 EECAPITULATION OF CHAPS. XXXII. AND XXXIII. [Ch. XXXIII. 



deposited, liare sunk to an extreme deptli ot more than 11,000 



f( 



mean 



than a few hundreds. 



must 



lij^potliesis now proposed, that a greater number have arisen 

 from the sinkinsf down than from the elevation of rocks. 



seems 



above explained, that the constant repair of the land, and the 

 subserviency of our planet to tlie support of terrestrial as 

 well as aquatic species^ are secured by tbe elevating and 

 depressing power of causes acting in the interior of the 

 earth; which, although so often the source of death and 

 terror to the inhabitants of the globe — visiting in succession 

 every zone, and filling the earth with monuments of ruin and 

 disorder — are nevertheless the agents of a conservative prin- 

 ciple above all others essential to the stability of the system. 



Recapitulation of Cliajpters XXXII. and XXXIII. — I will 

 now recapitulate the principal conclusions arrived at in this 

 and in the preceding chapter. 



1. The primary causes of the volcano and the earthquake 

 are to a great extent the same, and connected with the deve- 

 lopment of heat and chemical action at various depths in the 

 interior of the globe. 



temperature 



many 



when it was in a state of igneous fusion, a temperature which 

 they suppose to have been always diminishing and still to 

 continue to diminish by radiation into space. 



3. The spheroidal figure of the earth does not of necessity 

 imply a universal and simultaneous fluidity, in the beginning; 



may 



jj 



must 



— y 



be allowed, by the gradual operation of the centrifugal force, 

 acting on yielding materials brought successively within its 

 action by aqueous and igneous causes. 



that the precessional 



4. 



Mr. Hopl 



motion of the earth could not be such as it now is, unless 

 the solid crust was from 800 to 1,000 miles thick; but the 

 precessional movement is consistent with the supposition of 



CH' 



*^"" 





l^^': P .;. 



pia)' 



be 



sol 



^ 



tbtbe 



Jescen 



the 



s 



heat ^-•■' 

 iiBply such a 

 as must inst 



6. The hj 

 heU restin! 



absence of i 

 and flow in ' 



7. The hj 

 supposed sol 

 nucleus in c( 

 to lower, 01 

 because the 

 (lirectfon wc 

 of the earth 



8. Assumi 



for iiifeiTinnj- 

 flaiditj- lie, -a 



™lcanie actic 

 globe long po 



•Cerent pn ^ > 

 ^' Tlie qua 



^ 





111 





