Page:A Treatise on Geology, volume 2.djvu/180

 166 vein is worth following for its rich lateral strings; and it is a common notion of miners that such appendages are influential on the productiveness of a vein.

One of the most curious accidents which affect a vein fissure, is its bending or expanding against particular layers of rock, so as to constitute what, in the mining country of Aldstone Moor, are called "flats," or lateral extensions parallel to the stratification. These are often cavernous in the middle, and yield beautiful crystallisations.

Veins sometimes appear as one united mass, due to one single or uninterrupted deposition of mineral substances; in other cases there are divisions in the veins, or by the side of them, which contain clay or quartz ribs, or in some other way give indications of successive rents in the same general direction. Such appearances have been often noticed (as by Werner, Carne, Fox, &c.), and considered as capable of explaining, in some instances, the curious and very common accident of portions of the neighbouring rocks, enveloped in the mass of the veins, always near to and even opposite to the parts whence they were disjoined. Such portions of the neighbouring rocks are called "rider" and being frequently traversed and impregnated by the vein substances, acquire a characteristic aspect; which being found again not infrequently in the rock on the sides of the vein, especially where "strings" pass off from the mass of the vein, such bounding rocks are said to be "ridered."

In this manner, by (successive?) nearly parallel rifts in the rocks, which all received mineral depositions, a "strong vein" becomes of almost indefinite width, even 30, 40, or more feet across, and often bewilders the miner, unable to interpret or follow the seemingly capricious manner of the mineral aggregation.

The rocky boundaries of the veins are often somewhat peculiar in character near the vein: sometimes, as in the case of rock dykes, they appear harder than the rest of the rock; at other times some difference of