73 



TAB. CXXXIX. 



In examining the Bitumens, it is difficult to say whether 

 they pass from Naphta and Petroleum to Pitch and Asphal- 

 tum, by a regular gradation, through the elastic kind, or 

 not, as they seem to pass naturally from one to another 

 without them. Most people would have been satisfied with 

 the series had the elastic ones not occurred. By accidentally 

 breaking a mass of crystallized Carbonate of Lime, was 

 found in a hollow a black mineral pitch, in a liquid state : 

 see the left hand hot torn figure. This has now become con- 

 densed and elastic, but not so much so as the substance in 

 the last figure. The crust or outer surface is brownish, 

 with more elasticity, and may be separated by the nail like 

 the middle figure, which shows the outside and inside. The 

 left hand figure shows also hollows in the centre of the 

 outer crust, or external parts, something like the mouth of a 

 minute crater ; giving a strong idea of its having been once 

 in a state of powerful ebullition from that hole. This is a 

 darker-coloured Bitumen, possessed of greater elasticity than 

 any that has been before noticed. Among specimens this 

 should be placed as the darkest, and perhaps nearly the last of 

 the elastic sorts. The next in this plate is a more indurated 

 Bitumen, much resembling the last (at first sight)j and 

 which seems to have been in a state of ebullition, from 



