Economic Geological Deposits. — Crosby. 265 
(a) Substitution deposits in calcareous rucks. The importanl examples 
are too numerous for detailed citation, hut include the following: The 
copper deposits, in part, of the Morenci, Bisbee, and Globe districts of 
Arizona, ami of the Santa Rita district. New Mexico; and the lead-silver 
•ores of the Leadville, Ten Mile, Monarch, Eagle River. Aspen, and Rico 
districts, of Colorado; pf Galena and Carbonate, South Dakota: of Bing- 
ham, and Big and Little Cottonwood Canons, the Crismon-Mammot h 
yein and the Horn Silver mine. Utah; a'nd of the Eureka and White 
Tine districts. Nevada. 
(b) Substitution deposits in siliceous rocks. Owing to the greater insolu- 
bility of the rocks, the well-identified examples under this type are less 
•extensive, but include the following: The hematite of the Penokee- 
Gogebic district and the Mesabi range, and possibly of Iron .Mountain. 
Mo.: the copper oresof Butte. Montana (extensive replacements of gran- 
ite along small fissure vei us); the veins of native copper on Keweenaw 
Point: and many so-called gold and silver veins, including the Comstock 
lode. 
ir. Aqueous deposits of superficial origin (sedimentary 
rocks, etc.). — The history of the superficial aqueous deposits 
is so much less obscure than that of the subterranean depos- 
its that comparatively brief statements will suffice. Follow- 
ing the order of the lithological classification, we have : 
1. Mechanical deposits (fragmental rocks). — These have 
been deposited from suspension, and include : 
(a) Normal fragmental rocks, including the conglomerate, arenaceous, 
and argillaceous groups, consolidated and unconsolidated. 
(b) Placer deposits, fluvial and marine, ancient and modern. The 
sorting action of water has effected the concentration in the rock, at the 
time of its deposition, of one or more useful minerals, such as gold, 
platinum, iridosminc. cassiterite, and magnetite, and corundum, topaz, 
diamond and other gems. This type may be compared with the origi- 
nal disseminations in igneous rocks, a single constituent and not the en- 
lire rock being useful. It is quite unnecessary to cite the numerous 
gold placer districts of this country. Marine placers occur at Port Or- 
lord. Oregon, and Yakutat bay. Alaska. The gold placers of the Black 
Hills are in part Quaternary and Recent, and in part the basement beds 
of the Potsdam sandstone. The beds of conglomerate iron ore mantling 
Iron Mountain ami Pilot Knob. Mo., show the sorting and concentrating 
.action of water and are virtually ancient placers. 
2. Chemical deposits (chemically-formed rock, etc. ). — The-. 
have been deposited from solution by : 
(a) Oxidation. The examples include: Bog limo'nite, with pond and 
lake ore: Clinton hematite, oolitic ore, due to deposit ion of iron oxide in 
concentric coats about minute grains of quartz; and fossil ore; when' 
.the iron oxide is deposited in or replaces waterwom fragments of calca- 
reous organisms; beds of limonite and red hematite in various forma- 
