4? INTRODUCTION. 
to the width of several feet. The vein at Dalcooth 
mine, in Cornwall, varies from two or three to forty feet 
and upwards ; and, in some parts, it contracts so as to 
be little more than six inches across. 
8. In Cornwall the first traces of tin and copper are 
usually found at the surface of the ground, and thence to 
the depth of 80 or 100 feet beneath ; and it is said that 
no miner has ever yet seen the bottom of a vein, although 
several have been wrought to the depth of more than 
1000 feet. The veins of these metals have, in some in- 
stances, been worked to the length of three or four miles. 
9. It is frequently observed that metallic veins are 
separated, from the substances they intersect, by a thin 
wall, or lining, of minerals different from these sub- 
stances, and also by a layer of clay on each side of the 
vein. It is also remarked that the same substance which 
forms the outer coat of the vein is often intermixed 
with the ore, or forms layers alternately with it. This 
has usually tjie denomination of matrix or gangue. 
10. There are few mines of any considerable depth 
that would not be flooded with 'water from internal 
springs were not means adopted for drawing off this 
fluid. The steam engines that are employed for this 
purpose in some of the Cornish mines are so powerful 
as to discharge incessantly, both by night and day, a 
quantity of water, equal to at least 1000 gallons, or 
near twenty hogsheads, every minute. 
SYSTEMATIC ARRANGEMENT OF 
MINERALS. 
11. To a superficial observer, perhaps nothing would 
appear more easy than to describe a mineral. This, 
