Economic Geological Deposits. — Crosby. 267 
far simpler, in most cases, than the actual deposits; for a 
classification, to have any value, must isolate causes and ex- 
hibit phenomena in their elements. Thus, for example, ac- 
tual veins are usually combined with impregnations and 
replacements, and on the surface mechanical, chemical, and 
organic deposition go hand in hand ; and we can not ordina- 
rily say of a deposit that it belongs to this or that type, but to 
this or that combination of types. 
Outline of the Classification. 
A. Deposits of igneous origin (igneous rocks). 
i. Igneous deposits of subterranean origin (plutonic rocks). 
(a) Normal plutonic rocks. 
(b) Excessively basic plutonic rocks. 
(c) Original disseminations in plutonic rocks. 
(d) Sublimates in fissures. 
ii. Igneotis deposits of superficial origin (volcanic rocks). 
(a) Normal volcanic rocks or lavas. 
(b) Excessively basic volcanic rocks. 
(c) Original disseminations in volcanic rock. 
id) Sublimates on lava. 
B. Deposits of aqueo-igneous origin. 
('. Deposits of aqueous origin. 
i. Aqueous deposits of subterranean origin (vein rocks, etc.). 
1. A'eins. or deposits in pre-existing cavities. 
(a I True fissure veins. 
(1)) Crushed-zone or shear veins. 
(c) Joint or nash veins. 
(d ) [nterbedded veins. 
(e) Neck veins. 
- (f ) Crenitic veins. 
(g) < 'avern veins. 
(Ii) Brecciated cavern veins. 
2. impregnations. 
(a) Concretionary deposits, not metasomatic. 
(b) Concretionary deposits, metasomatic. 
(c) Amygdaloidal deposits. 
(d ) Interstitial deposits. 
(e) Metasomatic deposits in calcareous rocks. 
if) .Metasomatic deposits in fragmental rocks. 
(g) Metasomatic deposits in igneous rocks. 
Ih) Metasomatic deposits in met a tnorph ic rocks. 
3. Subst it ut ion deposits. 
(a) Substitution deposits in calcareous rocks. 
(Ii) Substitution deposits in siliceous rocks. 
