THEORY OF THE EARTH. 415 



disturbed any previous set or sets of strata: and, at 

 as many periods as disturbances of sets of strata can 

 be proved, at so many have there been distinct forma- 

 tions of igneous rocks, or protrusions of ignited fluids. 

 These are Revolutions, of, or on, the surface of the 

 Globe, inferred to be general or partial, according to 

 the extent of the demonstrable effects. Their relative 

 dates are inferred by those of the strata on which they 

 have acted : while every later one must have caused a 

 fresh disturbance in all that was anterior, under each 

 division of rocks. 



The disturbance is proved, chiefly, by a change of 

 parallelism in sets of strata: adding, in most cases, ap- 

 pearances in them, indicating the tumultuary motion 

 of large fragments ; and, in recent ones, the absence 

 of limestones and the remains of animals : as thus 

 does a new parallelism indicate a new period of repose. 

 And, under these disturbances, strata are changed from 

 their original positions, elevated, bent, fractured, and 

 chemically affected, while also penetrated by veins of 

 the igneous rocks ; as these themselves are, when more 

 antient, by veins of the more recent ones. 



The final past effects of all this are ; to have caused 

 frequent changes in the places of the land as it relates 

 to the sea, with varying changes in its elevation ; to 

 have gradually multiplied the number and variety of 

 the rocks, as also to have augmented their general 

 quantity, compared to that of the fluid portion of the 

 globe; to have destroyed or diminished, at several 

 periods, previous organic creations ; and to have accu- 

 mulated their spoils in limestones, and those of vege- 

 tables in coal. And the final present ones are; to be 

 extending the habitable surface, in various ways, and 

 to be preparing strata, beneath the waters and on the 

 dry land, which are apparently destined to a similar 

 fate, at a future period, and with similar results. 



