WEISSENBACH ON VEINS. 57 
In consequence of the continual transitions and combinations which 
the phenomena of mineral ves exhibit, it is not possible to distin- 
guish them into groups as is done mm rock-formations. In the groups 
of mineral veins the author can only recognise various products, mo- 
dified by locality or degree of development, of one great formative 
process of nature, or the individual aspects of one vast geognostic 
formation. The families of mineral veins which can be accurately 
distinguished will always retain a totally diverse import from the 
formations of mineral veins which are here established ; they can only 
be considered as members of one and the same formation. 
The author distinguishes various classes of veins, of which the 
mineral veins form only one class, viz. 
Sedimentary veins :—formations in open fissures caused by mechanical 
filling-up from above. 
Friction-veins :—consisting of the products of friction or other me- 
chanical destruction of the neighbouring rock. 
Stalactitic or infiltration-veims :—fissures filled by incrustation. 
Plutonic or rock-veins [Dykes] :—fissures filled with mineral masses, 
which also occur as plutonic mountain rocks. 
Secretion-veins :—laminee, geodes, and vein-like formations in the in- 
terior of rocks, formed by the secretion or accretion of matter from 
the surrounding rock. 
Mineral veins. 
The first five classes are distinguished according to the way and 
manner in which a fissure has been filled, and thus can scarcely be 
put im opposition to or classed with mineral veins, separated on 
wholly diverse grounds, or from the nature of the mass which fills 
them. Yet we will not differ with the author for this want of clas- 
sification, which would have given him occasion to impart to the 
public his careful, multiplied and extensive observations on mineral 
veins, had not this portion of the work, as well as that on plutonic 
or rock-veins, been left incomplete. 
It will be understood that in this classification various groups of 
veins may be distinguished in each class, and especially among the 
mineral veins, and that when these are designated veim-formations 
the author understands only groups of veins especially resembling 
each other, which may be chosen from the variety of veins, partly as 
various grades of development, partly as local modifications of the 
general formation of mineral veins. 
Did any perfect certainty exist regarding the manner and various 
processes connected with the production of veins ; did their phzeno- 
mena exhibit beyond doubt, at once their causes and origin, then the 
knowledge of the epoch and manner in which they had been produced. 
would furnish much more precise characters for their division ito 
formations. But at present, these processes, and the origin of mineral 
veins, are far too little known, and the most diverse views prevail 
regarding them, which based only on one portion of the phenomena 
cannot be brought into harmony with the others, and even often con- 
tradict them. Much is still wanting before a satisfactory general 
theory of veins can be established, but this only the more requires that 
