Outlines of Geology- 39 



Lastly, as to the sources and origin of coal. Upon these sub- 

 jects geologists, as usual, have amply indulged their inventive 

 faculties. Every thing tends to show the vegetable origin of coal, 

 and a regular succession might 'be shown, commencing with wood, 

 little changed, and ending with coal, in which all traces of organic 

 texture are lost. Yet even in the most perfect coal we frequently 

 find some relic, some trace of a vegetable, or some remains of 

 fibrous texture that announces its ligneous origin. In the leaves 

 that occur in Bovey coal, Mr. R. found resin and extractive mat- 

 ter ; and what is more to the purpose, he found a substance hav- 

 ing properties intermediate between resin and bitumen, and there- 

 fore partaking partly of vegetable and partly of mineral cha- 

 racters ; and more lately the same substance has been found in 

 the principal coal field of Staffordshire. Perhaps, therefore, an- 

 tediluvian timber and peat bog may have been the parent of our 

 coal strata, but then, how has its immersion been effected ; is it 

 merely by the agency of water, a kind of decay and rotting down of 

 the wood ; or has fire been called into action, torrefying the ve- 

 getable matter, and has the pressure under which this heat has 

 operated prevented the escape of volatile matters, and caused them 

 to assume the form of bitumen ; and are those reservpirs of com- 

 pressed carburetted hydrogen which I have mentioned as causing 

 blower^ to be ascribed to such mode of formation ? The discussion 

 of these subjects might be prolonged, but it would end in nothing 

 satisfactory. The theories that have been invented to account for 

 our coal formations are full of weak and assailable points ; the 

 further we pursue them, the less do they satisfy us, and the more 

 discordant do they seem with the phenomena they are intended 

 to explain. 



We should almost conclude, from the dogmatical air of some 

 writers upon this subject, that they had seen the agents they 

 speak of in active operation ; that they had fathomed the depths 

 of the globe, and measured its central heat ; but if we compare 

 our planet to an orange, and remember that we have not as yet 

 penetrated its rind ; if we compare it to the pasteboard globe of 



