268 Ansii'cr lo a Matliemaiical Question. 



to judge of the internal part of the ground. For the external 

 part presented to the sight only hills with gentle inflexions, at 

 that time covered with the finest harvest. 1 was struck with the 

 idea that I walked over a land inhabited by a nation of gnomes, 

 occupied down to a great depth in opening new paths in the 

 bowels of the earth. 



Lastly, I observed from another high ground, that this mineral 

 country is confined by two valleys or great fractures in the strata, 

 beyond which the veins no more appear externally. 



I conic to the author's ojjinion, " that if the iieins v^'erejis- 

 sures, the quality of the rock could have little influence on the 

 ore." There is no reason given !>y the author for his assertion, 

 tior is the case a general one. In the veins of Derbyshire, the 

 same gangiie continues without iiiteniiption, and without dif- 

 ference in the ftuidamental material, through diflerent kinds of 

 strata ; but it contains galena only when it pervades the lime- 

 stone strata. This is a fact^ but no1)ody that I know has un- 

 dertaken to explain it. It would be incumljent on the author 

 to prove that it is a constant effect, in order to give it as a 

 general case, that the iiatiire of the rock has an influence on that 

 of the veins. But in this again he shows that he does not know 

 the great mineral country of the Hurtz. The whole of that 

 chain consists of schistns, and there is a great variety in the con- 

 tent of the vei7is. Besides gatenct, furnishing by smelting lead 

 containing silver, which is the greatest mineral product of the 

 Hurtz, there are veins of copper and of iron ores, very near one 

 another, and in some places crossing each other. 



These are facts, but till now they give no clew that leads to 

 their explanation. The author does not increase our knowledge 

 in that respect : on tlie contrary, in contradicting Werner's sy- 

 stem concerning the veins, which I think I have now proved, 

 he throws obscurity on points assented to by the greatest num- 

 ber of mineralogists, without substituting any thing to that 

 system. 



XLVII. Dr. Gregory, in Answer to Mr. Harvey's Mathe- 

 matical Question. 



To Mr. Tilloch. 



Dear Sir, — /as it will probably be expected that I should pay 

 some attention to Mr. Harvey's question at p. 233 of your last 

 number ; allow nie to say a word or two, consistently with the 

 brevity you require. 



In 



