OF NATURAL PHILOSOPHY. 285 



have been instrumental in the production of those 

 changes of level, and those violent dislocations 

 which we perceive to have taken place. 



(320.) At all events, in accounting for those 

 changes, geologists have no longer recourse, as for- 

 merly, to causes purely hypothetical, such as 

 a shifting of the earth's axis of rotation, bringing 

 the sea to overflow the land, by a change in the 

 place of the longer and shorter diameters of the 

 spheroidal figure, nor to tides produced by the at- 

 traction of comets suddenly approaching very near 

 the earth, nor to any other fanciful and arbitrarily 

 assumed hypotheses ; but rather endeavour to con- 

 fine themselves to a careful consideration of causes 

 evidently in action at present, with a view to ascer- 

 tain how far they, in the first instance, are capable 

 of accounting for the facts observed, and thus legi- 

 timately bringing into view, as residual phenomena, 

 those effects which cannot be so accounted for. 

 When this shall have been in some measure accom- 

 plished, we shall be able to pronounce with greater 

 security than at present respecting the necessity of 

 admitting a long succession of tremendous and 

 ravaging catastrophes and cataclysms, epochs of 

 terrific confusion and violence which many geo- 

 logists (perhaps with justice) regard as indispens- 

 able to the explanation of the existing features of 

 the world. We shall learn to distinguish between 

 the effects which require for their production the 

 sudden application of convulsive and fracturing 

 efforts, and those, probably not less extensive, 

 changes which may have been produced by forces 

 equally or more powerful, but acting with less irre- 



