310 Scientific Intelligence, [April, 



IV. On the Question as to the Existence of Metallic Veins in the Transition 

 Limestone of Plymouth. By Mr. Prideaux, and the Rev. Richard 

 Hennah. 



(To the Editor of the Annals of Philosophy.) 



SIR, Plymouth, Feb. 15, 1823. 



Observing some doubts expressed in your last number of the accu- 

 racy of Mr. Hennah's statement, that our " lime rocks contain no 

 metallic veins;" I am induced to offer you some reasons for coincid- 

 ing fully in his opinion. 



I believe I speak much within compass in saying, that the face of 

 that rock is open to an extent of above four miles ; and that more than 

 half of it has been in regular work within the last five years. For 

 nearly the whole of this extent we get to the upper surface, and in 

 several different places we trace its repose on, and alternation with, the 

 clay slate, for a considerable distance. The cliffs and quarries are 

 from 50 to 150 feet high, and cut the strata at all angles. And the 

 limestone itself forms only the hilly boundary of the sea, nine-tenths 

 of it being exposed. 



I think, therefore, it is almost impossible that a metallic vein, how- 

 ever minute, existing in it, should have escaped detection. 



The specimen you describe, as found at Cat*Down, looks like a fact 

 in opposition to this conclusion ; but I have several times traced the 

 whole course of the extensive quarries in that situation from top to 

 bottom (though my opportunities are not so frequent as Mr. Hennah's) ; 

 and although varieties of crystallization, and not metallic specimens, 

 were my pursuit, the latter could hardly have escaped me ; nor have 

 the men employed in the quarries ever mentioned such appearances in 

 my hearing. 



That the mines of Tavistock yield specimens of crystallized carbon- 

 ate of lime, bearing abundant marks of their metallic connexion, and 

 much like the one in question, you are doubtless aware. I should 

 hardly suppose, therefore, that you could have been deceived in it, 

 though the little mineral dealers here are likely enough to make the 

 mistake. But the considerations above related appear to me so deci- 

 sive that were I to find a detached specimen, such as you describe, at 

 Cat-Down, any where but in situ, I could not believe it to be the pro- 

 duce of those quarries, where I have seen nothing to which it appears 

 at all related. I am, Sir, your most obedient, 



John Prideaux. 



SIR, Citadel, Plymouth, March 8, 1823. 



I perused, a few days ago, in the 26th number of the Annuls of 

 Philosophy, a quotation from a recent publication of mine, on the 

 " Lime Rocks of Plymouth," in which I state that it is my opinion, 

 that they contain no metallic veins, which quotation is accompanied 

 with an account of a particular specimen of quartz, &c. making part of 

 a collection said to be from our quarries ; and with a suggestion, that 

 the circumstance merited further inquiry. Being myself desirous to 

 promote any investigation, which has for its object the correction of 

 any error which I may have inadvertently fallen into, or the establish- 

 ment of any point which I believe to be true, I hope your correspon- 



