THE FORMATION OF DEPOSITS 21 
which occurs above tin in the Cornish mines (Fig. 9), still 
requires a moderate temperature for its formation, as is shown 
by its frequent formation in a contact ore. Lead, silver, and 
snc are found in still higher levels, and are often deposited 
'n grits and limestone which show less alteration by heat 
\ 
J 
Slate: 
or 
soft) 
200fe} 
B00f, 
Fi6. 9.—A Corepzr TiN Lope. 
The Passage of copper lodes (Cu) in slate into deeper tin lodes (Sn) in 
granite. East Pool and Wheel Agar Mine, Cornwall, (After 
Collins.) 
N, N, the north lode, Cu Sn W—north branch from the main lode contain. 
ing ores of copper, tin, and tungsten. 
and pressure than the rocks associated with most copper 
Ores. Mercury, the characteristic ore of the younger 
mountain systems, is often found in small quantities in 
hot springs and their sinters, and its chief ore-fields 
are in bands intensely shattered by the Middle Kainozoic