GEOGNOSY AND GEOLOGY. 1351 
They are of different, often very considerable size, and are sometimes lined 
with the most magnificent crystallizations. A large druse was opened at 
Andreasberg a few years ago, and brilliantly illuminated with torches. 
The splendor of the appearance produced by the reflection of light from the 
thousands of crystal faces is described as having been almost overpowering. 
Such drusy cavities most generally occur towards the upper extremity of 
the vein, decreasing in number with the descent. 
Ores are said to lie disseminated in the gangue when they are interspersed 
in small particles, and imbedded when aggregated in larger masses. 
Gangue and ore may likewise alternate in layers parallel! to the sides of the 
vein, as seen in pl. 43, fig. 20. Here the layer a, immediately lining the 
cavity of the vein, consists of brown blende; the succeeding one, 8, of 
quartz; the layer c, of fluor spar; d, of brown blende again; e, of barytes ; 
f, of radiated pyrites; g, of barytes; h, of fluor spar ; 7, of radiated pyrites ; 
k, of calcareous spar; and /, of a drusy cavity, lined with crystals of 
calcareous spar. In some veins the ores include spheroidal masses of the 
gangue, so as to present an annular appearance. An argentiferous galena 
of this character occurs at a mine not far from Klausthal in the Hartz, for 
the above-mentioned reason called “ring and silver thread.” 
The connexion existing between mineral veins and the inclosing rocks is 
quite different under different circumstances. Sometimes the former 
separates readily from the latter, either owing to a natural absence of 
connexion, or to a decomposition and weathering of the outside. At other 
times the vein mass is so intimately united with the rock as to cause great 
difficulty in the separation. 
When a vein is not precisely perpendicular (a rake vein) it may either 
hang (form an obtuse angle with the descending vertical) or le (form an 
acute angle with the vertical). 
A very remarkable relation sometimes exists between the vein mass and 
the including rock, with respect to their internal and external peculiarities ; 
these relations, however, cannot be combined into any definite system. 
The principal facts of the kind are, that the vein, on the whole, is weak in 
proportion to the hardness of the rock; also, that the same vein may 
continue through different strata, and be of different contents in different 
rocks, and that the gangue may or may not exhibit an affinity to the 
rock. 
Neighboring veins, which run more or less parallel, communicate only 
by their ramifications or threads; they may, however, intersect each 
other at various angles, these being either right or acute and obtuse 
(pl. 39, figs. 85, 82). The veins sometimes intersect, run together for a 
short distance, and then separate, as seen in fig. 83. 
When such intersections take place it is in most cases possible to 
distinguish the intersecting from the intersected. A vein, A, cut by a vein, 
B, sometimes is continued in precisely the same course; it frequently, 
however, experiences a displacement to one side or the other of the original 
direction, termed a shift (fig. 84). The continuation of the intersected 
vein on the opposite side may narrow or expand (fig. 85); it may ramify 
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