the Formation of the supeijicial Part of the dole. 453 



iThe power of man to penetrate the earth is very limited : few 

 mines have been sunk to so great a depth as five hundred yards; 

 vet by the fractures and dislocations of the strata we are fre- 

 quently enabled to measure their thickness as they rise in suc- 

 cession to the surface over a considerable extent of country. 

 But the regularity of rise is limited, and the strata are lost as We 

 proceed fmther or incline in an opposite direction, so that the 

 greatest aggregate thickness that has been any where examined 

 does not perhaps exceed eight miles. The diameter of the earth 

 is nearly eight thousand miles, to which the depth of surface 

 that we are acquainted with bears no greater jjroportion tlian 

 the thickness of a wafer to the diameter of a three-feet artificial 

 globe. 



Were we to bear these facts in mind, the fractures, dislocations, 

 and overturnings of rocks and strata, and even the up -heaving 

 of the bed of the ocean, phaenomena which appear so over- 

 whelmning to the imagination, sink into comparative insignifi- 

 cance : instead of being astonished at these changes, we should 

 be more disposed to admire the stability of nature, in preserving 

 the incrustation of the globe so perfect amidst the conflict of 

 tumultuous elements. There are a few leading facts in geology, 

 which we may consider as clearly ascertained by existing phae- 

 nomena. Among these we may enumerate, 1st, That the pre- 

 sent continents were once covered by water. 2nd, Tliat the 

 strata in which organic remains occur, were formed in succession 

 over each other. 3d, That every regular stratum was once the 

 uppermost part of the globe. Let us further inquire, whether 

 there remain any appearances in nature that may indicate in 

 what manner these strata were formed, or the source from v.'henc^ 

 the matter of which they are composed was evolved. The two 

 great agents in the decomposition and formation of mineral sub- 

 stances, either artificially or in nature, are water and fire : any 

 theory which should exclude the agency of either from the for- 

 mation of the crust of the globe would be manifestly defective. 



The numerous volcanoes scattered over the globe abundantly 

 prove the existence of fire in the deep recesses of the earth. 

 During a former state of our planet, this internal fire must have 

 been more intense than since the records of authentic history. 

 This is shown by the remains of mighty volcanic craters, which 

 far exceed any that are active at the present time ; for, the cra- 

 ters themselves being formed by the eruption of volcanic matter, 

 their size bears evidence to the magnitude of their former ope- 

 rations. 



It is natural to inquire what part these tremendous agents 



have performed in the oeconomy of nature : Are they accidental 



a])pendages, or essential parts of the terrestrial sy':tem ? The 



F f 3 geologists 



