Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/125

 Rh miners give the name of Killas. Here, as in the Hartz, it is very rich in ore, and for this reason, Klaproth proposed to call it Saxum Metalliferum Cornubiense.

In low situations especially, grauwacke-slate has a very great resemblance to clay-slate; in other places it decomposes, and passes into the state of marl.

The grauwacke formation occupies a very considerable extent in Cornwall. Without having traced it step by step throughout, I believe I may safely say, that it prevails without interruption on the southern side of the chain from the mouth of the Hamoaze (the name given so the river Tamar after its junction with the Tavy) to that of the river Hel, thus occupying a space of about forty miles from east to west. It may possibly happen that in this course some other rock belonging to the same formation may be found in subordinate beds, but whatever it is, I do not think it can be of any great extent.