ECONOMIC GEOLOGY
mountain-movements of the Upper Carboniferous and Lower
Permian, e.g. most of the British, German, and Mediterranean
 ores; but those of Leadville and most other fields
in the Rocky Mountains and the Andes are Eocene.
The lead ores may be classified as follows :—
A. PriMARY ORES—
I. Fissure lodes: Freiberg; Pennines; Leadhills, etc.,
Comstock, Nevada; Cceur d'Alene, Idaho; Linares,
Spain.
II. Replacement Ore-Bodies—
(4) Massive primary ore-bodies: Bawdwin, Burma;
Broken Hill; Rhodesian Broken Hill; Sullivan,
British Columbia.
(6) Ores with igneous rocks :—
1. Contact ores beside plutonic masses: South Hill,
Idaho.
2. Ores associated with quartz-porphyry sheets:
Leadville, Magdalena, Kelantan, etc.
B. SecoNpDARY OREs—
III. (a) Disseminations: Missouri.
{b) Flats and ore bodies due to descending solutions:
Missouri; Silesia; Aachen; Rhodesia.
IV. Sedimentary ores: Commern; St. Sebastian, Gard;
Mendip Hills.

)8

SECTION A. Primary OREks

Fissure LopEs—GERMANY, BriTAIN, SPAIN, COMSTOCK—
The primary lodes depend mainly on the nature of the country
rocks. The classical primary lead lodes are at Freiberg in
Saxony, where mining was begun by refugees from Central
Germany in the tenth century. The mining field is in the
Erzgebirge or Ore-Mountains of Saxony in a dome-shaped
uplift of gneiss, on which rest fossiliferous Cambrian rocks.
The uplift produced an intersecting network of fissures, with
more than 1100 lodes. They are classified into four chief
groups, which were formed at two dates. The older series
includes three groups: (1) the Noble-Lead lodes with 340
veins, are in two series trending at right-angles, one to