1822.] On a Sevfion of the'Shdta, ^c. 22^ 



As according to the statement that the great hmestone has 

 prodaOed as much lead, as all the others taken together, and 

 as this bed is 21 yards thick only, we may reckon, that very. 

 productive ground is limited to a space or thickness equivalent 

 to the double of this, or about 42 yards, or in the language . 

 most usual in the English mines, to about 21 fathoms. 



This will doubtless appear very extraordinary to other miners, 

 who know no such limit to their operations, and who see thin 

 veins rich in the metals, to depths that are only limited by the- 

 power that has as yet been appUed to carry on the operations 

 by which mining is pursued. 



The actual thickness of the beds, which are productive of. 

 lead in various proportions, however, appears to be about 225 

 yards, or 112 V fathoms, as v/e infer, from a passage in p. 212,. 

 where it is said that they are those that are between the grind- 

 stone sill, and the five fathom limestone ; and which, by lelcr- 

 ring to the section, we find occupy the above space But here 

 is then, as above shov/n, one half the value contained in 10^. 

 fathoms ; and the other half, occupying 102 fathoms, would be' 

 of course better if it were also comprised in an equal space, 

 and making together, as we have stated it, 21 fathoms. 



This is a small allowance of workable ground, and it must be 

 rich indeed to produce what it does, either in the number and 

 extent of the veins, or in the degree in which these veins are. 

 replenished with ores. 



Mr. Forster has, in the same page (212,) quoted Mr. Price, to - 

 show that the richest parts of the Cornwall strata are, for cop- 

 per, from 40 to 80 fathoms deep ; and for tin from 20 to 60 ; 

 which would make it appear, that in other countries the metali- 

 ferous parts of the rocks were also limited to certain depths* 

 Why has Mr. Forster referred to an authority written so long , 

 ago, and when probably such a notion did prevail, but whichr is 

 certainly not true ? There are many recent accounts, of the 

 mines in Cornwall, in papers in the Geological Transactions, by ^ 

 Dr. Berger, by Mr. Phillips, and others, an4 tliere are the sec- 

 tions before mentioned by Mr. Thomas, by which it will appear 

 that the rocks in Cornwall are not divided, into strata, in the 

 sense the word is used'in Mr. Forster's book, and that copperrv 

 ore is found at all depths to which the powers of man have . 

 been able to follow it, and that no indication has presented 

 itself by which it can be concluded, that it may not yet be pur- 

 sued further, and by a continued application of the skill and 

 energy which make the Cornish mines so remarkable — some 

 of them being already full 200 fathoms under the level of the 

 «ea. 



The account of the curiously stratified state of the district, 

 exhibited in the section, is followed by some tables of strata in 

 other places, as at Arkengarth dale, and Swale dale in York- 

 shire ;, and also by a long extract from Mr. Farey's works, with 



ifew Series, vol. hi. q 



