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