Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/143

Rh is under the necessity of passing in the usual course of his occupation in the sinking of shafts and driving of levels and adits, often prove the occasions of great hindrance and loss. There is a narrow channel of a remarkably fine grained substance consisting of compact felspar and chlorite, running in the direction of east and west, a little north-west of Redruth, which is so exceedingly hard as to have obtained the technical name of Ire-stone or Iron-stone. It was met with in driving an adit towards a mine, the Old Pool, I believe, and it has often been told me, that it was so remarkably compact in one place as immediately to turn the point or edge of every tool, so that it was found impossible to drive a hole deep enough to employ the blast by gun-powder: the miner was compelled little by little to pick through that part of it, in doing which the seat-board was not once moved forward during the space of 12 months.

The schist of Cornwall varies much in colour as well as in hardness. It passes from lightish grey through the shades of slate colour to that inclining to a reddish hue, which is considered to be promising as to the occurrence of tin. But that which is esteemed the most kindly both for copper and tin, as well as the least expensive in the working, is of a light grey colour inclining to slate. This kind of schist is easily broken, and may be left without much support, and is therefore what the miner terms feasible ground, but it often passes in depth into a far more compact kind, of a dark colour, inclining to blue.

It has already been noticed that there are veins in Cornwall, which as they are found almost uniformly to traverse the east and