of Devonshire and Cortiivall. 113 



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 

 MetaU'iferum Cornubiense.j- 



In low situations especially, grauwacke-slate has a very great 

 resemblance to clay-slate ;:j: 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 

 to 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. |1 



* It is also this variety which has been analysed by Ivirwan, and which he classes with 

 the Il'ornstoues. He found that 100 grains contained 



Silica . 60 

 Alumina 25 

 Magnesia 9 

 Iron . 6 



100 



+ Klaproth's Mincralogical Obserrations on Cornwall, p. 7. 



% La fermentation (qu'on me permette, dit M. de Trebra, de designer sous ce nom, 

 cctte force de la nature qui met tout en mouvement dans le regne mineral) peut trans- 

 former Xa grau-ccacke en un schiste argileux qui peut durcir et devenir un jaspe, si cette 

 fermentation cesse ou diminue. Nouvelle Theprie de la formation des filons, par Wer- 

 ner, p. 54. 



§ In some parts of Cornwall this marl mixed with sea sand and sea weed is used as a 

 manure. 



jl The Rev. Mr. Gregor of Creed, with whom I conversed on this subject, informed 

 ine, that going along the coast from Grampound to Fowey, a limestone is found, which 



P 



