9 



Bovey is rendered extremely probable by the geognostic 

 relations of that coal. From this to the harder lignites, 

 suturbrand and jet, the transition is so gradual, that there 

 seems no reason to limit the power of water to produce the 

 effect of bituminization in all these varieties ; nor is there 

 aught in this change so dissonant from other chemical 

 actions, as to make us hesitate in adopting this cause." 

 Satisfied that jet, the bituminous lignite which approaches 

 the nearest to coal in its chemical characters, is the result of 

 the action of water on vegetable matter, Dr. MaccuUoch was 

 induced to try if this substance could, by heat under pres- 

 sure, be converted into coal : the result of his experiment 

 was, that the produce exhibited the true characters of coal, 

 having not merely the colour and inflammability, but the 

 fracture of coal and its odour on burning.* These expe- 

 riments and observations, taken with those of Mr. Hatchett, 

 appear to be sufficient to set the question, as to the vege- 

 table origin of coal, at rest. 



The vegetable origin of naphtha, petroleum, and as- 

 phaltum, is not yet positively ascertained. Amber, from its 

 being found generally in beds of fossil wood ; the blue clay 

 resin found at Highgate and at Sheppey among the pytrified 

 wood ; and the retinasphaltum of Mr. Hatchett, discovered 

 among the Bovey coal, may either owe their origin to the 

 changes effected in vegetable matter during its subterraneous 

 deposition, or may be vegetable resins, the original product 

 of the trees which they accompany, and which, from their 

 resinous nature, may have resisted the bituminizating 

 process. 



The argillaceous ironstone nodules which accompany 

 coal, contain, with the remains of many other unknown 

 vegetables, parts of various cryptogamous plants, the recent 

 analogues of a very few of which have been said to be found 



* Transactions of the Geological Society, vol. i. p. 2. 



c. 



