58 GEOLOGICAL MEMOIRS. 
the pheenomena should be accurately studied, described and considered 
from various points of view. 
The sedimentary ves are on the whole rare, and seem of sub- 
ordinate interest, though they may frequently give some information 
regarding the more recent formations, and in this pomt of view deserve 
more general and accurate observation than has hitherto been be- 
stowed on them. 
The friction-veins are filled with matter produced by the crushing 
and rubbing of the neighbouring rock itself. They have very often 
given occasion to the formation of vems filled with foreign matter, 
and consequently belonging to an entirely different class, and by the 
union of the two produce veins possessing a very mixed nature. The 
larger part of mineral veins are at least partially connected with the 
formation of friction-veins. 
The author distinguishes here,— 
. Veins with products of decomposition. 
. Veis with products of friction. 
. Veins with products of compression. 
. Veins with angular fragments (Brockengesteinen). 
. Veins with rounded stones (Kugelgestein). 
Veins in the coal formation. 
Doe Gd 
The first three of these divisions are altogether identical, and pass — 
completely the one into the other. The products of decomposition, 
rubbing and compression are usually conjoined; it is only in rare 
cases that they can be separately distmguished. The occurrence 
with mineral veins, and also with slips or dislocations, partly in the 
coal formation, partly in other sedimentary rocks, is highly important, 
and. still presents a wide field for observation. Vems enclosing angular 
fragments, also spheroidal stones and ramifications uf the lamelle of 
the wall-stone (auch Spharengestem und Umzweigungen von Neben- 
gesteinschaalen), are most common among mineral vems. They are 
not wanting however among the sedimentary and stalactitic vems. 
Included in these fragmentary rocks are the friction-conglomerates, 
formed on the limits between eruptive masses and the rocks pre- 
viously existing. The veins, enclosmg rounded stones, the author 
considers were most probably formed in this manner; that the walls 
of the fissure had a repeated rubbing motion on each other, and in this 
manner have ground the angular fragments that came between them 
into a spherical form. The fragments and distmet produce of the 
grinding process fill up the intervals between the balls, and ac- 
quire, from the access of moisture and processes of decomposition, a 
new consistence similar to that of the origmal rock. As mstances of 
this formation are mentioned the Schurfer-vein, near the large air- 
hole (Lichtloch) at Altenburg, where the balls consist of a brownish- 
red felspar porphyry ; the globe-vein (Kugelgang) in the deep mine 
at Zwitterstock, in which larger or smaller balls of gneiss occur. 
Among veins in the coal formation some very interesting examples 
from the mining district of Plauen are described, which however 
are more local, and furnish no general type of the dislocations common 
in other coal districts. | 
—_—a ae he 
