VEINLETS IN THE SILURIAN AND DEVONIAN 61 
some of the calcareous tufa now forming in places on the surface. 
These fissures are possibly due to the solution and removal of under- 
lying salt beds or perhaps to other superficial disturbances, since 
the deposits were evidently formed in the belt of weathering. 
TYPES OF VEINS 
Structurally the veins are of two different types: one fibrous, 
the other more or less coarsely crystalline and non-fibrous. The 
former are composed either of gypsum or calcite, the crystal fibers 
extending transverse to the strike of the veins, which run in all 
directions, but are generally parallel to the bedding. These veins 
are lenticular and continue for short distances only. The non- 
fibrous veins usually consist of gypsum or calcite, but the calcite 
veins sometimes contain accessory quartz and pyrite. They are 
more persistent and more uniform in width than the fibrous veins, 
and most of them are vertical or steeply inclined. The evidence 
indicates that each type had a different mode of formation. 
SOURCE OF THE VEIN MINERALS 
In the veins under consideration there can be no question as to 
the source of the vein minerals, for it is evident that they have been 
derived from the neighboring rocks. The veinlets found in the 
gypsum-bearing strata of the Salina are composed of gypsum, while 
those occurring in the limestones, waterlimes, and calcareous shales 
consist essentially of calcite. It is not the purpose of the writer, 
however, to imply that the vein minerals found in other and larger 
veins have usually had a similar source. 
DESCRIPTION OF THE FIBROUS VEINS 
The fibrous (satin spar) veins are larger and more abundant 
in the gypsum-bearing strata, probably because of the greater 
solubility of gypsum as compared with calcite. As a rule they are 
less than 3 cm. in width and from 20 to 50 cm. in length, but in 
places they have a width of over 10 cm. and extend for distances 
of many meters. Most of the veins are highly lenticular in form; 
where a vein thins out it may be replaced by another a little to one 
side, so that the ends overlap. Veins frequently split into two or 
