Analysis of the viagiietlcal Pijr'itea. 135- 



fersdorf, and Breitenbrunn in Saxony ; but, having received 

 some specimens from the right honourable Charles Gre- 

 ville, F. R.S., I was struck with their resemblance to the 

 pyrites of Breitenbrunn, which happened at that time to be 

 in my possession ; and, upon trial, I found that they were 

 magnetical, and agreed with the latter in every particular. 

 Their magnetic power was such as strongly to afiect a well- 

 poised needle of about three inches in length; apiece of 

 the pyrites, nearly two inches square, acted upon the needle 

 at the distance of four inches. 



The powder (which is blackish gray, with but little me- 

 tallic lustre) is immediately taken up by a common mag- 

 net; but the pyrites docs not act thus on the powder, nor 

 on iron filings, unless it has been placed for some time be- 

 tween magnetical 'bars ; then, indeed, it acts powerfully, 

 turns the needle completely round, attracts and takes up 

 iron filings, and seems permanently to retain this addition 

 to its original power. 



In the specimens which I obtained, the north pole wai 

 generally the strongest. 



This pyrites was found in Wales, about the year 179S, 

 by the honourable Kobert Greville, F.R.S., who sent the 

 specimens above described to his brother the right honoura- 

 ble Charles Greville, with the follow ing account : 



" It is found in great abundance in CaernarvonshirCj 

 near the base of the ujountain called JSIocl Elion, or pro- 

 t)ably with more accuracy Moel yElia, and opposite to the 

 mountain called Alynydd Mawr. These mountains form 

 the entrance into a little close valley, which leads, to. Cy- 

 wellin lake, mar Snowdon, a little beyond the hamlet of 

 Bettws. 



*' The vein appears to be some yards in depth and 

 breadth, and seems to run from north to south, as it is 

 found on Mynydd Mawr, which is across thp narrow val- 

 ley, and opposite to Mod ^lia." 



Mr. Robert Greville, in another part of his letter^ statcsi 

 that copper ore has been worked in several of the adjacent 

 places, and that, many years ago, captain Williams, of 

 Glan yr Avon, employed some miners at the place where 

 this pyrites is found, but tlie undertaking proved unpro- 

 ductive. Yellow co])per ore is certainly in the vicinity ; 

 for some portions of it were adhering to the specimens 

 vhichhave been mentioned; and I shall here observe, tli;U 

 the stone which accompanies the magnetical pyrites is a 

 variety of the lapis ollans, or pot- atone, of a pale grayish 

 green, containiner smooth cubic crystals of conunon pyrites. 

 "14 § IIJ. 



