31 1 Strufturt of the Earth. [Book VI. 



cafes produce fpontaneous inflammation in the early 

 ages of the world, whereas, as the earth grows older, 

 thefe materials muft be exhaufted, or rather formed 

 into other combinations. Many mountains, we know, 

 are of volcanic origin, and therefore many of them of 

 a date long pofterior to the sera of creation. 



Such appears to be the moft rational account of 

 the ftruclure of the earth, as far as we are warranted 

 by actual experiment, or well authenticated obferva- 

 tion. The fucceeding chapters of this book will 

 ferve to explain more fatisfactorily the different apr 

 pearances of various portions of the globe. I fhall 

 therefore proceed, without further digreffion, to treat 

 more particularly of mountains, volcanoes, and the other 

 phenomena more immediately connected with this 

 branch of natural hiftory. 



