174 The Founders of Geology LECT. 



which, though generally used in its modern sense, em- 

 braced some rocks of more basic character. 



He showed that the whinstones correspond so closely 

 to modern lavas in structure and composition, that they 

 may be regarded as probably also of volcanic origin. But 

 he did not suppose that they had actually been erupted at 

 the surface, like streams of lava. He found them to occur 

 sometimes in vertical veins, known in Scotland as dykes 

 a term now universal in English geological literature and 

 sometimes as irregular bosses, or interposed as sheets 

 between the strata. He regarded these rocks as masses of 

 subterranean or unerupted lava, but the grounds on which 

 he reached this conclusion were not always such as the 

 subsequent progress of inquiry has justified. The deduction 

 was correct, but the reasoning that led up to it was partly 

 fallacious. Hutton argued, for instance, that the carbonate 

 of lime, so commonly observable in his "whinstones," 

 indicated that the rock had been fused deep within the 

 earth, under such pressure as to keep that mineral in a 

 molten state, without the loss of its carbonic acid. Like 

 the other mineralogists of his day, he was not aware that 

 the calcite of the amygdales has been subsequently intro- 

 duced in solution, and that the diffused calcite in the body 

 of the rocks generally results from their decomposition by 

 infiltrating water. Much more appropriate were his observa- 

 tions that the whinstone has greatly indurated the strata 

 into which it has been injected, even involving fragments 

 of them, and reducing carbonaceous substances, such as 

 coal, to the condition of coke or charcoal ; that it has been 

 inserted among the strata with such violence as to shift, 

 upraise, bend, or otherwise disturb them, and that it can 



