The whole body of the Granite of the Mount is traversed by an uninterrupted series of quartz veins, which run parallel to each other with wonderful regularity. They are very nearly vertical, and their direction is east and west. On the north-east side of the Mount many of them can be traced into the incumbent slate; a circumstance which strongly supports the idea of the cotemporaneous origin of these two rocks. In the investigation of these veins the Mineralogist may pass many an hour with satisfaction, we shall therefore point out some of the more leading phenomena which deserve his attention. _De Luc_ observed that "that part of the vein termed in Cornwall the _Capel_, and on the Continent _Selebanque_, and which is the first stratum adherent to the sides of the fissures, changes as it passes through different kinds of strata, sometimes consisting of white _Quartz_, sometimes of _Mica_." _Dr. Forbes_[27] says, that "occasionally, though rarely, the line of division between the vein and the rock is tolerably distinct; frequently, however, there is rather an insensible gradation of the matter of the one into that of the other, than an obvious apposition of surfaces." The exterior parts of the veins consist of a bluish _quartz_, very compact, and uniformly containing a great deal of _Schorl_. This _schorlaceous_ character is much more distinct towards the sides or walls of the veins, their centre being generally pure _quartz_; and, commonly, crystallized. In most of the veins there is a central line, or fissure, which divides them into two portions; this is formed by the close apposition and occasional union of two crystallized, or, as they may be called, _drusy_ surfaces. Since Veins must be considered as having once been the most active laboratories of Nature, so may they now be regarded as her most valuable cabinets of mineralogy. In those of Saint Michael's Mount may be found crystals of _Apatite_, from a very light to a very dark green colour, and exhibiting most of the modifications of form[28] which are common to that mineral; _Oxide of Tin_; _Felspar_; _Mica_ beautifully crystallized in tables; _Topaz_ in small whitish or greenish crystals,[29] both translucent and opaque, and which are extremely numerous, many hundred being observable on the face of some small blocks of granite that have fallen from the precipices. _Pinite_ has been said to have been also discovered in this spot. Besides which may be found that rare mineral, the _Triple Sulphuret of Copper,_ _Antimony, and Lead_; _Sulphuret of Tin_; _Malachite_; _Fluor Spar_; and _Wolfram_. The occurrence of this latter mineral was, we believe, first noticed in the earlier edition of the present work, and is important in as far as its presence is generally supposed to afford decisive evidence of the primitive formation of the mountain masses in which it occurs.