§ 16. GEOLOGY ELUCIDATED BY ASTRONOMY. 49 



oxygen and hydrogen. Metals may in like manner be 

 converted into gases ; and in the laboratory of the chemist, 

 all kinds of matter easily pass through every grade of 

 transmutation, from the most dense and compact to an 

 aeriform state. TTe cannot, therefore, refuse our assent 

 to the conclusion, that merely by the dissolution of the 

 existing combinations of matter, the entire mass of 

 our globe might pass into a gaseous or nebular condi- 

 tion. 



16. Geology elucidated by astronomy. — From the 

 light thus shed by modern Astronomy upon many of the 

 dark and mysterious pages of the earth's physical history, 

 it appears probable that the dynamical changes which have 

 taken place in our globe — all the transmutations of its 

 crust revealed by geological investigations — may be refer- 

 able to the operation of the one, simple, and universal 

 law, by which the condensation of nebular masses into 

 worlds, through periods of time so immense as to be beyond 

 the power of human comprehension, is governed. 



The internal heat of the globe — the evidence afforded by 

 the crystalline condition of the lowermost rocks of a pre- 

 vailing higher temperature in an earlier state of the earth — 

 and the elevations and dislocations of its crust which have 

 taken place, and are still going on — all refer to such an 

 origin, and to such a constitution of our planet, as that 

 contemplated by the nebular theory. Nor is the elevatory 

 process peculiar to the earth, for Venus, Mercury, and the 

 moon, exhibit evidence of a similar action ; and in the two 

 former the mountains are of an enormous altitude.* In a 

 philosophical point of view, the present physical epoch of 

 our globe " is that of the fluidity of water, which is the 

 nebulous bed or stratum last condensed, and which exerts 



* This subject is ably treated in Sir H. de la Beche's "Researches 

 in Theoretical Geology." 



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