20 Astronomy and Geology compared. PT. i. 



Incomplete and defective as the evidence of facts in 

 Greology appears to be, yet much has been established 

 from the mine of facts, which is still rich in new 

 materials ; and the tendency must be to strengthen 

 and improve our knowledge as fresh stores come to 

 light. Many of the principles of Greology may be 

 considered as established, and future labours will 

 doubtless confirm them, and correct any existing 

 errors. 



The general conditions which geologists may con- 

 sider as being established are, first of all, the im- 

 measurable antiquity of the earth ; secondly, the 

 existence of different and separate periods indicated 

 by various strata containing the fossil remains of 

 animals and plants proper to them. The series of 

 these strata is never found inverted; particular 

 strata may be found wanting in any locality, but 

 older strata are never found over more modern for- 

 mations. It may be remarked that one great de- 

 fect pervades Greology, as far as it has yet been ex- 

 plored, which is the entire vagueness and uncertainty 

 of all its chronology. Whether the various epochs 

 embraced 10,000 or 50,000 or 100,000 or 5,000,000 

 of years is a calculation on which Geology has 

 hitherto failed to afford the slightest light, or to 

 make any estimate. 



