1 



ILLUSTRATIONS OF THE 



and broken figure of our continents, and the 

 identity of the mineral llrata on oppofite fides 

 of the fame valley, or the fame inlet of the fea ; 

 we Ihall fee abundant reafon to conclude, that 

 the earth has been the theatre of many great 

 revolutions, and that nothing on its furface has 

 been exempted from their effects. 



To trace the feries of thefe revolutions, to 

 explain their caufes, and thus to conned: toge- 

 ther all the indications of change that are found 

 in the mineral kingdom, is the proper objed of 

 a Theory of the Earth. 



But, 



though the attention of men 



may 



be 



turned to the theory of the earth by a very fu- 

 perficial acquaintance with the phenomena of 

 geology, the formation of fuch a theory requires 

 an accurate and extenfive examination of thofe 

 phenomena, and is inconfiltent with any but a 



L 



L 



very advanced itate of the phyfical fciences. 

 There is, perhaps, in thofe fciences, no refearch 



than this ; none certainly where 



ix ; vv^here the appearan- 



more ard 



dely 



the fubjedl is fo complex ; v 

 ces are fo extremely diverfified, or fo 

 fcattered, and where the caufes that have ope- 

 rated are fo remote from the fphere of ordinary 

 obfervation. Hence the attempts to form a 



theory of the earth 



of very modern origin 



and as, from the fimplicity of its fubjecl, alt 



nomy 



the eldeft, fo, on 



of the com 



plexnefs 



