439 



experimentally the contortions of certain strata, and the manner in 

 which the phenomena had been effected by upheaving forces acting 

 under compression. He subjected various rocks ot igneous origin 

 to chemical analysis, and succeeded in establishing their relative de- 

 grees of fusibility. He gave an original and perspicuous account of 

 the true mode of formation of volcanic cones ; and whilst he pointed 

 out that Monte Somma was simply the segment of a vast volcano, 

 from the flank of which the present Vesuvius had arisen, he showed 

 the intimate analogy between the dykes of lava of the former and the 

 ancient trap-dykes of our continents. If, in tracing the revolutions 

 of the surface of the earth, he was led to attribute too much to the 

 influence of one great diluvial current, we must recollect that in this, 

 his only dereliction from the principles of Hutton, his conclusions were 

 founded on a striking class of phenomena first observed by himself; 

 and that the diluvial theory (though in a modified sense) has still the 

 support of many of our most eminent geologists. To a mind so ac- 

 customed to speculate upon the intense energy of volcanic pheno- 

 mena, it was a natural inference that the fractures and dislocations 

 of mountain -masses have been produced by paroxysmal efforts of na- 

 ture, — in short, by mighty earthquakes, and their accompanying ele- 

 vations, depressions,, and eruptions. 



Much, however, as we owe to him for his many accurate observa- 

 tions of nature, our debt of gratitude must specially be acknowledged 

 for his successful application of chemistry to geology, without which, 

 one essential condition of the theory of Hutton would not have been 

 established, as it now is, upon an immovable basis. The important 

 discovery of carbonic acid by Black, which was destined to lead 

 to the solution of many occult terrestrial phaenomena, was at first 

 cited by the Wernerians as destructive of the very basis of the theory 

 of the igneous consolidation of the strata of the earth, it appearing 

 impossible to explain the formation of crystalline marble from earthy 

 carbonate of lime, by the very agent which drives off the gaseous con- 

 stituent in every lime-kiln. To obviate this difficulty, the founder of 

 the new theory propounded, that the heat by which rocks had been 

 solidified was applied under enormous pressure ; that in consequence 

 effects had taken place entirely differing from those which manifest 

 themselves under the mere pressure of our atmosphere ; and that 

 under such circumstances carbonate of lime might have been reduced 

 to a state of fusion without calcination. Though the genius of Hutton 

 had thus divined the true cause of the phaenomena in dispute, that 

 great man shrunk from the prosecution of experiments which might 

 prove the truth of his hypothesis, being persuaded that the immensity 

 of natural objects was far beyond the reach of man's imitation. It 

 was reserved for Hall to have the glory of demonstrating the truth of 

 the doctrine of his friend ; — " the conjectures of genius," as he tells 

 us, " at length ceased to appear extravagant ; the mist which ob- 

 scured the objects being dissipated by degrees, they appeared in their 

 true colours, and a distant prospect opened to his view of scenes be- 

 fore unsuspected." To his ardent mind the realization, upon the 

 surface of the earth, of that which had occurred below the deep abyss 



