127 



, LETTER XIII. 



BITUMENS. ...PARTICULAR KINDS DESCRIBED. ...KNOWN TO WRI- 

 TERS OF THE HIGHEST ANTIQUITY.. ..HISTORY OF NAPHTHA, 

 PETROLEUM, AND ASPHALTUM, FROM THE MORE ANCIENT 

 NATURALISTS. 



THE substances, the nature of which next requires our considera- 

 tion, are those which are generally denominated bitumens. Naphtha, 

 petroleum, mineral tar, mineral pitch or maltha, asphalt, elastic 

 bitumen, jet, mineral coal, amber, and mineral tallow, are the diffe- 

 rent substances which, by general consent, are placed in this class. 



The propriety of dwelling on the history of these substances, in 

 a work devoted to secondary fossils, may not, perhaps, at first sight, 

 appear; but when their origin is more closely traced, and when 

 they are considered, in connection with the other substances, which 

 appear to be derived from the same origin ; not only will their im- 

 portance be perceived, but their right to be considered, themselves, 

 as secondary fossils, will, I trust, be evident. 



Bitumen is a substance of a peculiar kind, seeming to partake 

 both of an oily and resinous nature, and is found either buried in, 

 or proceeding from, different parts of the earth, in different states 

 of consistence. The different degrees of consistence, as well as the 

 variety of colour, which the more simple of these substances possess, 

 according to the valuable observations of Mr. Hatchett, depend 

 on certain changes, which have taken place in the same substance. 

 We will first notice the more simple state in which these substances 

 exist. 



NAPHTHA (oleum terra), which Mr. Hatchett considers as bi- 



