THE FORMATION OF DEPOSITS 17 
sand and clay. Some constituents of the lithosphere are 
deposited chemically or organically in such beds as gypsum, 
salt, limestone, coal, and ironstones, 
The barysphere doubtless passes to the lithosphere through 
an ore-zome, rich in silicates and metallic sulphides. Above 
the ore-zone is a basic’ zone composed mainly of heavy 
silicates, and known as the sima from the first letters of its 
chief constituents, silica and magnesia ; still higher is an 
acid-zone of light silicates, with much alumina and alkalis ; 
it is known as sial, from the symbols of silicon and aluminium. 
The upper part of the lithosphere would probably at first 
have contained but few metals. The metallic constituents 
of the barysphere, ore-zone, and sima have been raised to 
the surface by the intrusion of basic igneous rocks, which 
have carried upward large quantities of iron and manganese, 
and facilitated the ascent from the ore-zone of mineralized 
water, 
SOURCE OF THE METALS In OrES—Some species of pyroxene, 
amphibole, and olivine contain iron and manganese as essential 
constituents; and gs metals in nature are seldom pure it 
is not surprising that small quantities of copper, cobalt, 
ind nickel are found in ferro-magnesian minerals, The 
search for various metals in igneous rocks was inspired by 
the theory of Bischoff (1847) that the contents of lodes are 
derived from the rocks beside them by lateral secretion. His 
disciples, such as Forchhammer {1855) and F. Sandberger 
(1882 and 1885), claimed to have found all the common 
metals in the minerals of igneous rocks. Thus olivine, 
augite, and hornblende yielded Sandberger arsenic, bismuth, 
cobalt, copper, lead, nickel, tin, uranium, and zinc; and the 
Micas yielded arsenic, bismuth, copper, lead, tin, uranium, and 
zine. "Many later chemists! have reported traces of the less 
common metals in igneous rocks. Some of these claims are 
dubious, as the amounts are too small for reliable determina- 
tion. In other cases the elements have been introduced 
after the formation of the rock and are secondary constituents; 
©-g. the oft-quoted gold in the diorite of the Ayrshire Mine, 
'E.g. copper in fresh olivine dolerite in the Globe district, Arizona ; 
Ransome, U.S.G.S., Prof. Pap. 12, 1903, P. 128; J.H. I, Vogt estimates 
the amount of nickel as ‘03 per cent. in gabbros and norites, and ‘0005 
Per cent, in granite, Zcon. Geol., xviii, 1923, p. 328.