ECONOMIC GEOLOGY 
for the solutions may have impregnated the wall rock with the 
lode minerals. 
Lodes consist of earthy minerals or veinstones, of metallic 
constituents, and of fragments of country rock. The com- 
monest veinstone is quartz. Next in importance is calcite, 
which is especially abundant in limestones. Fluorite, barite, 
and dolomite are frequent in volcanic regions, and in deep- 
seated lodes. Less common are the felspars, rhodonite (a 
pyroxene composed of silicate of manganese, MnSiO,), and 
garnets. Tourmaline, usually in the black variety known as 
schorl, and topaz are common in lodes that have been formed 
by superheated acids. Mica of economic value occurs under 
similar conditions. The metallic constituents sometimes 
form a minute proportion of the lode; but they give it its 
special character and value. The metals are sometimes 
native, but are usually present as compounds, chiefly sul- 
phides, oxides, and carbonates. The fragments of country 
in the lode may have fallen into the fissure, or have been 
torn from the walls by the faulting, or be parts that resisted 
replacement by the lode-forming waters, Large masses of 
sountry rock in a lode are known as horses. That terms is 
sometimes applied to the country between two arms of a 
branching vein, and also to beds of sandstone which have 
filled stream channels in coal. The term * horse” is con- 
veniently restricted, in connection with alode, to the original 
meaning of a mass of country which is completely surrounded 
by the lode. 
The veinstones and rock debris found in a lode are some- 
times grouped together as * gangue,” a French form of the 
German word ** gang” which means the whole lode. The 
rock debris in a lode is known in Australia as muliock ; 
the term has been rejected as miner's slang, but as it was 
similarly used by Chaucer, that objection is invalid. Some 
lodes consist of a fault-breccia of mullock, with the inter- 
spaces filled with veinstones and metalliferous constituents, 
True brecciated lodes have been broken into fragments by 
faulting or pressure after their formation, 
Tae Term Reer—There is much confusion between the 
terms reef and lode due to a reversal of the meaning of reef. 
Owing to the heaviness of the metallic grains the richest 
layer in an alluvial mine js usually at the base. When all