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598 GEOTECTONIC (STRUCTURAL) GEOLOGY. [Book IV. — 
known as Butzen (cones) and Nester (tufts). The size of these in- 
definite accumulations of ore varies from mere nests up to masses 
800 feet or more in one direction by 200 feet or more in another. 
Hematite, brown iron-ore, and galena not infrequently occur in 
this form in limestone, as in the “ pockets ” of hematite in the Car- 
boniferous Limestone of Westmoreland. The “gash” or “ rake” 

Fie. 310.—SroTion oF MINERAL DEPOSITS IN LimusTONE, DERBYSHIRE (B.). 
a a a’, Carboniferous Limestone with intercalated bed of pyroxenic lava or “toadstone” 
(b); hhh h, joints traversing the limestone, 7 g, k d, m ce, veins traversing all the 
rocks and containing veinstones and ores; f, spaces between the beds enlarged by 
solution and filled with minerals or ores (“flat-works”); p p, large irregular 
cavernous spaces dissolved out of the rock and filled with minerals and ores. 
veins of galena in the north of England occur in vertical joints 
of limestone which have been widened by solution, and are some- 
times completely cut off underneath by the floor of shale or sand- 
stone on which the limestone lies. Lenticular aggregations of ore 
and yeinstone found in granite, as in the south-west of England, 
where they are known as Carbonas, cannot be due to the infilling 
of chambers dissolved by subterranean solution. They are usually 
connected with true fissure-veins; but their mode of origin is not 
well understood. 
Stock-works are portions of the surrounding rock or “country ” 
so charged with veins, nests, and impregnations of ore that they can 
be worked as metalliferous deposits. The tin stock-works of Corn- 
wall and Saxony are good examples. Sometimes a succession of 
such stock-works may be observed in the same mine. Among the 
granites, elvans, and Devonian slates of Cornwall, tin-ore has 
segregated in rudely parallel zones or “ floors.” At Botallack, at 
the side of ordinary tin lodes, floors of tin-ore from six to twelve 
feet thick and from ten to forty feet broad occur. 
Origin of mineral veins.— Various theories have been proposed 
to account for the infilling of mineral veins. Of these the most note- 
worthy are—(1) the theory of lateral sezregation,—which teaches that 
the substances in the veins have been derived from the adjacent rocks 
by a process of leaching, or solution and redeposit; and (2) the theory 
of infilling from below,—according to which the minerals and ores were 
introduced dissolved in water or steam, or by sublimation, or by 
igneous fusion and injection. 
The fact that the nature and amount of the minerals, and 
especially of the ores, in a vein so often vary with the nature of the 
surrounding rocks seems to show that these rocks have had a certain 

