I 
( 48° ) 
III. A Second Letter to Dr . Rutty, R. S. Seer. 
containing farther ObferVaftons towards compojing 
a natural Hiflory of Mines and Metals. ©^ 
Vr. Nichols, Prjtl Anat . Oxon, and S. 5. 
c j D ear SIR , 
* \i • 
I N my laft I acquainted you with fome Particulars 
relating to Mines in general, and that the Loads in 
Cornwal yielded Iron, Tin, Lead, and Copper. 
\ ' * v *' \ 
Of I R O N. 
Of all the Subftances concurring to form the ter- 
reflrial Globe, Iron probably bears the greateft Share j 
as it not only abounds in raoft Kinds of Stone, 
(hewing it felf in Varieties of Crocus, all which gain 
a more intenfe Colour by Fire^ but enters likewife 
greatly into the Compofition of common Clay j as may 
be judged from the Similitude of Colour between 
Clay and dry Iron Oar ^ from the eafy Vitrification of 
Clay \ from the Refemblance between Clay fo vitrify’d 
and the Clinkers of Iron^ from its deep red Colour 
after Calcination j and laftly, from its yielding pure 
Iron, by being burned with Oil. 
But while Iron is thus entangled with other Bodies, 
it rarely employs the Care of the Miner } who finds 
the Expence of reducing it to Metal too feldom bal- 
lanced by the Price it yields: For which Reafon, tho’ 
we frequently meet with large and rich Loads of Iron, 
yet 
