63 



rocks ; and it is sufficient to observe, that by equally satisfactory, 

 though, perhaps, less self-evident reasoning, the same origin may 

 be ascribed to all the rest. In this manner it will be seen that 

 by a strict process of inductive reasoning, we are enabled to 

 arrive at conclusions no less interesting than important with re- 

 gard to the nature of those powerful agents/ &c. &c. 



" Such are the reasonings by which it has been concluded that 

 the above rocks are of an igneous origin, which, forsooth, is called 

 a strict process of induction ! Fortunately for our underground 

 operations, our practical men laugh at such absurdities, and are 

 guided by better reasoning, founded on daily experience ; but it 

 is on young men, such as surveyors, &c, who have been taught 

 such doctrines in the academies, and are too often placed in re- 

 sponsible posts, where such ideas lead to bad results, and who 

 are under the impression that every vein or rock of what they 

 call trap is the relic of a former volcano," &c. &c. 



One of the most usual effects of heat upon limestone is to de- 

 prive it of its carbonic acid and reduce it into a white powder. 

 We know of no instance of lime having been reconverted into a 

 crystalline limestone by heat. Chalk, when intersected by veins 

 of any substance containing carbonic acid, is partially converted 

 into marble by the impregnation or absorption of the acid from the 

 veins. One of the most direct objections to the supposed igne- 

 ous rocks was first drawn from the appearances of the calcareous 

 strata in contact with basalt ; but the assumed igneous element, 

 with its effects, appears by its supporters to possess extraordi- 

 nary properties, — remaining unaffected in water as well as in the 

 air, hot or cold, according to circumstances ; capable of convert- 

 ing limestone into lime, or lime into limestone, as they may feel 

 disposed to apply it, and totally uncontrolled by any fixed 

 principle or the known laws of heat. Much has been written 

 against the theoretical deductions of Werner ; but however in- 

 consistent they were, those which have been founded on the 

 assumed igneous agency are much more arbitrarily drawn, most 

 irregularly applied, and totally irreconcilable with the observed 

 phenomena, and have tended quite as much as the dogmas 

 of our predecessors to bring the geological science into disre- 

 pute. 



Those who feel an interest in this subject, i. e. the contact of 

 hornblende veins with limestone, coal, &c, may examine the 



