288 Earth tonfijls of Strata. [Book VI. 



cept, indeed, in fome of thofe immenfe mountains, which 

 have exifted from the creation, or at leaft from the 

 deluge, where the matter, from whatever caufe, ir, 

 more homogeneous, the earth is found to confift of 

 various ftrata^ or layers, which differ according to the 

 ci'rcumftances of climate and fituation. The furface, 

 in general, evidently confifts of a confiifed mixture of 

 decayed animal and vegetable fubftances and earths 

 rudely united together j but when we have penetrated 

 below the furface, we find the materials of the globe 

 arranged in a more regular manner. Sometimes, in- 

 deed, we find heaps -of ftone, which do not confift of 

 layers, but are confufed mafies of unequal thicknefs, 

 and are called rocks. The ftrata are, in general, ex- 

 tended through a whole country, and, perhaps, with 

 Ibme interruptions and varieties, through the globe 

 itfelf. Thefe extenfive bodies are found moft regular 

 when the country is flat, being, in that cafe, nearly 

 parallel to the horizon, though frequently dipping 

 downwards in a certain angle ; in many places the 

 beds have a wave, as where the country confifts of 

 gently waving hills and vales j here too they generally 

 <3ip. la travelling a mile we, perhaps, pafs through 

 ground compofed moilly of fand, in another mile Ve 

 find it, perhaps, compofed of clay 3 and this is occa- 

 fioned by the edges of the different ftrata lying with 

 an obliquity to the horizon. By the fame kind of 

 projection, mountains, or ridges of mountains, are pro- 

 duced, which, in general, have what is called a back 

 and a face, the former fmoother and the latter more 

 rugged. We generally find too, on one fide of a 

 mountain, a more gradual afcent than on the other, 

 which is occasioned by the ftrata, which have rifen 

 above the general level of the country, being abruptly 

 broken o\ Mountains are in general more abrupt 



toward* 



