14 Principles of Geology. 



it evident that some of these irregular operations had been comple- 

 ted in certain strata before the next rocks were deposited upon them. 

 For in Somersetshire, coal measures, highly inclined, lie beneath 

 and are concealed by horizontal beds of red marl. Therefore, their 

 highly sloping position must have been determined before the depo- 

 sition of that rock: and in the same country great faults, which ele- 

 vate the coal seams seventy yards, produce not one inch of displace- 

 ment in the red marl which lies above. Assuredly then, internal 

 convulsions of the earth occurred at intervals during the deposition 

 of rocks ; and by studying their relative antiquity, we obtain plain 

 evidence of the lapse of time between the formation of the several 

 strata. Examples of the same kind are well known in Yorkshire, 

 where inclined coal measures are covered (as at Garforth) by nearly 

 horizontal magnesian limestone, which is unbroken by the vast dykes 

 in the subjacent coal. There are good grounds for believing that the 

 highly inclined position of the primary strata is not original : it is ex- 

 tremely probable, and, indeed, generally admitted, that these stupen- 

 dous ranges of mountains have been uplifted by some mighty inter- 

 ternal agency. It is certainly true that the greatest dislocations of 

 the secondary strata are in the vicinity of primary mountains ; and, . 

 though it must not pass as a general or established rule, we may some- 

 times refer the disruption of secondary to the same agency which ' 

 produced the elevation of primary rocks. 



Having considered the internal structure of our planet, and shewn 

 how the rocks succeed one another in a fixed order, and rise suc- 

 cessively to the surface; how variously they are filled with the monu- 

 mental reliquiae of organic beings which existed during the remote 

 ages, when the secondary strata were deposited beneath the ocean ; 

 and also examined the effects of convulsions within the solid sub- 

 stance of the earth; it becomes necessary to turn our views to the 

 surface. — The external features of the earth afford many interesting 

 subjects of reflection, and are replete with memorials of mighty 

 changes. Though it cannot be supposed that, by investigation of its 

 present appearance, -^ve should be able to determine completely its 

 former condition, enough is known to assure us that after the earth 

 was dried and made habitable, its whole surface was again submerged 

 and overwhelmed by an irresistible flood. Of many important facts 

 which come under the consideration of geologists, the " Deluge" is, 



