114 . Answer to Dr. Grierson^s Ohervations [Feb. 



have gone still farther. Why he afterwards, in p. 101, mentions, 

 that, excepting a small proportion of mechanical deposite that 

 accompanies the second porphyry formation ; and in p. 351, " that 

 primitive conglomerate forms a bed of inconsiderable maj^nitude," 

 without stating the reasons for the alteration, 1 cannot tell. 



The last circumstance I shall here notice is the singular meta- 

 morphosis, as t!ie Doctor calls it, that takes place upon the grau- 

 •u-ackc when it comes in contact with the granite. You have visited 

 St. Michael's Mount, and have found that the clay slate in the 

 neighbourhood of tlie veins contains so much mica as to have the 

 aspect of mica slate, an alteration which you will observe in all 

 similar situations ; and although the Doctor thinks, that because 1 

 could see no line of division at the Lowran between this altered 

 rock and the common grauwacke, I had no reason to conclude that 

 there was none, I must beg leave to differ from him, and to assure 

 him that I am more inclined to believe my own ej-es tlian any other 

 species of demonstration that can possibly be ottered. 



Dr. Grierson accuses me of laying stress upon the opinions of 

 the vulgar, when it suits my purpose ; an accusation which I 

 leave 5-our readers to judge whether he ought not to feel ashamed 

 of, when they peruse the following paragraph, which is the only 

 one in rny paper alluding, in the slightest degree, to the sentiments 

 of the Cornish miners ; a set of people, allow me to remark, much 

 beyond the class in which Dr. Grierson seems desirous to include 

 them : — 



" The only other rock of any importance in Cornwall is granite, 

 termed grauen by the common people — a name also given to clay 

 porphyry, a substance found pretty frequently in large veins, (Nos. 

 16, to 11), 2S, 48.) The shades of distinction chronicled by tluj 

 mineralogist, cannot be expected to attract the attention of the 

 miner, who knows !)ut two rocks, grauen and killas, throughout 

 the stannaries. It has been thought that a distinct rock was under- 

 stood by the term elvan ; but this is a mistake ; elvan may some- 

 times be greenstone, but in general is killas or granite, and is so 

 termed by the miner when he finds the rock harder to work in one 

 place than in another." 



Where or when Professor Jam.eson discovered the second forma- 

 tion of granite, to which Dr. G. refers that of Cornwall, we have 

 yet to learn. It is possible that such a discovery has led to some of 

 those alterations whicii that gentleman has found it necessary to 

 engraft upon the system of Ins master ; as we find the second 

 granite, when Mr. Jameson's last book was published, wis to be 

 found "only in veins," p. 106". And Dr. Grierson will remember, 

 that I purposely confined myself to the system of the master, not 

 that of the pupils. 



I now leave you and your readers to judge whether it was neces- 

 sary for Dr. G. to have put himself to so much pain in recording 

 my misstatements. Next time, however, I would recommend a 



