150 



ILLUSTRATIONS OF THE 



than another. The twolaft are certainly capable 

 of furnifliing both the carbonic and bituminous 

 parts ; and therefore, to derive thefe from dif- 

 ferent fources, is at leaft a very unneceffary com- 

 plication of hypothefes. 



138. Another explanation of coal, very dif- 

 ferent from any of the preceding, has lately been 

 advanced and fet up in oppoiition to the Hut- 

 tonian Theory. Mr Kirwan *, the only minera- 

 logift, I believe, who has attempted to derive both 

 the carbonic and bituminous matter of coal from 



■ 



the mineral kingdom, diftinguifhes between 

 Vv^ood-coal and mmeral-coal, and gives a theory 

 entirely new of the formation of the latter. 

 Wood-coal is that in which the ligneous ftruc- 

 ture is fo apparent, as to leave no doubt of its 

 vegetable origin ; mineral coal is that in which 

 no luch ftruciure can be difcovered, and is the 



J 



fame which Dr Hutton derives from the vegeta- 

 ble juices, and other remains, comminuted, dif- 

 perfed, carried into the fea, and there precipi- 

 tared, fo as to unite with different proportions of 



earth, and to become afterwards mineralized. 



I'hefe two fpecies of coal, which the Hutto- 

 nian theory confidtrs as gradations of the fame 

 fubllance, Mr Kirwan regards as perfedly di- 



* 



itintl, conftituting two minerals, of an origin 



and 



* Geol. Efl'ays, efiay vii. p. 1^0, 



