miners give the name of Killas.[1] Here, as in the Hartz, it is very rich in ore, and for this reason, Klaproth proposed to call it Saxum Metalliferum Cornubiense.[2]
In low situations especially, grauwacke-slate has a very great resemblance to clay-slate;[3] in other places it decomposes, and passes into the state of marl.[4]
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.[5]
- ↑ It is also this variety which has been analysed by Kirwan, and which he classes with the Hornstones. He found that 100 grains contained
Silica 60 Alumina 25 Magnesia 9 Iron 6 ─── 100 - ↑ Klaproth's Mineralogical Observations on Cornwall, p. 7.
- ↑ La fermentation (qu'on me permette, dit M. de Trebra, de designer sons ce nom, cette force de la nature qui met tout en mouvement dans le regne minéral) pent transformer la grauwacke en un schiste argileux qui peut durcir et devenir un jaspe, si cette fermentation cesse ou diminue. Nouvelle Théorie de la formation des filom, par Werner, p. 54.
- ↑ In some parts of Cornwall this marl mixed with sea sand and sea weed is used as a manure.
- ↑ The Rev. Mr. Gregor of Creed, with whom I convened on this subject, informed me, that going along the coast from Grampound to Fowey, a limestone is found, which appeared to him like that of Plymouth: he added, that it had been excavated in some places by the sea, and that the futures had since been filled up with a gravelly conglomerate.
