58 The Founders of Geology LECT. 



their cross-section, quite distinct from each other. I was 

 thus led to believe that prismatic basalt belonged to the 

 class of volcanic products, and that its constant and 

 regular form was the result of its ancient state of fusion. 

 I only thought then of multiplying my observations, with 

 the view of establishing the true nature of the phenomenon 

 and its conformity with what is to be found in Antrim 

 a conformity which would involve other points of 

 resemblance." 



He narrates the course of his discoveries as he journeyed 

 into the Mont Dore, detecting in many places fresh con- 

 firmation of the conclusion he had formed. But not only 

 did he convince himself that the prismatic basalts of 

 Auvergne were old lava-streams, he carried his induction 

 much further and felt assured that the Irish basalts must 

 also have had a volcanic origin. " I could not doubt," he 

 says, " after these varied and repeated observations that 

 the groups of prismatic columns in Auvergne belonged to 

 the same conformation as those of Antrim, and that the 

 constant and regular form of the columns must have 

 resulted from the same cause in both regions. What con- 

 vinced me of the truth of this opinion was the examination 

 of the material constituting the Auvergne columns with 

 that from the Giant's Causeway, which I found to agree in 

 texture, colour and hardness, and further, the sight of two 

 engravings of the Irish locality which at once recalled the 

 scenery of parts of Mont Dore. I draw from this recog- 

 nized resemblance and the facts that establish it a deduc- 

 tion which appears to be justified by the strength of the 

 analogy namely, that in the Giant's Causeway, and in all 

 the prismatic masses which present themselves along the 



