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Ch. IV.] 



HUTTONIAN THEORY. 



7o 



bottom of the ocean, they become afterwards altered and con- 

 solid ated by volcanic heat, and then heaved up, fractured, and 



contorted.' 



had never explored any region of active 



Hutton 



many 



volcanos, he had convinced 

 other trap-rocks were of igneous origin, and that many of 

 them had been injected in a melted state through fissures in 

 the older strata. 



com 



different aspect from that of ordinary lava, he attributed to 

 their having cooled down under the pressure of the sea ; and 



remove 



his friend, Sir James Hall, instituted a most curious and in- 

 structive series of chemical experiments, illustrating the 



crystalline 



ement and texture assumed by melted 



matter cooled under high pressure. 



The absence of stratification in granite, and its analogy, in 



miner 



Hutton to conclude that granite also must 



from 



and this inference he felt 



could not be fully confirmed, unless he discovered at the 

 contact of granite and other strata a repetition of the pheno- 



stantly by the trap-rocks. Resolved to 



test, he went to the Grampians, and 



nction of the granite and superincum- 



until he found in Glen Tilt, in 1785, 



mena 



masses 



the most clear and unequivocal proofs in support of his views. 

 Veins of red granite are there seen branching out " 



from 



micaceous 



limestone- The intersected stratified rocks are so 



exam 



in that locality most striking, and the alteration of the lime 

 stone in contact was very analogous to that produced by trap 

 veins on calcareous strata. This verification of his i 

 filled him with delight, and called forth such marks < 

 and exultation, that the p-uides who accompanied him 



ystem 



must 



a vein of silver or gold.* He 



same 



primary 



* Playfair's Works, vol. iv. p. 7-5. 



