Mr. William Phillips on the QxydofTin. 337 



Brongnlart says,* that " tin belongs exclusively to primitive coun- 

 tries, and even to those of the oldest formation ; for not only is it 

 found in veins and beds in granite, but also in masses, or dissemi- 

 nated in beds of gneiss, of micaceous shistus, and of porphyry. Veins 

 of tin adhere very often to the walls of the lode, by the rock which 

 encloses them ; they are always divided by other veins, and never 

 divide them. Tin therefore seems to be one of the metals of the 

 oldest formation : it is accompanied by substances which belong to 

 the same age, such as wolfram, arsenicated iron, topaz, quartz, fluated 

 lime, phosphated lime, hornblende, green and black mica, chlorite, 

 &:c. whilst carbonated lime, sulphated barytes, zinc, lead and silver, 

 substances which frequently accompany other metals, are rarely 

 found with it." All this may perhaps be true, in so far as it regards 

 depositions of tin in other countries, but I am induced to believe it 

 is not wholly so in regard to Cornwall, where veins producing tin 

 often occur in districts, both granitic and schistose, which it seems 

 difficult to ascribe to the primitive formation. 



Dr. Berger f in his paper on the physical structure of Devonshire 

 and Cornwall, says, " Here (Cornwall), as in the Hartz, it (grau- 

 wacke) is very rich in ore." In the term grauwacke. Dr. Berger, 

 following the example of Werner, seems to include every species of 

 that rock, usually called schist, and by the miner killas. He further 

 sayslf, " Grauwacke is one of the oldest of the secondary rocks." 

 Again, § in speaking of the discovery of uranium in Tin Croft 

 mine, which is situated at the foot of a granitic hill, but partly in 

 granite and partly in schist, its " being found in this district proves 

 that, contrary to the opinion of Werner, it may be met with in 

 secondary mountains." 



* Traite Elem. p. 191. 1 Gcolog. Trans, vol. 1. p. 113. 



X p. 111. §p. 170. 



Vol. ii. 2 u 



