204 Proceedings of the Royal Physical Society. 



not concentrated in any particular vein or pocket as was 

 supposed when the mine was being worked, but is dissemi- 

 nated throughout certain parts of the rock in irregular grains, 

 strings, and bunches, from the size of a pin's head up to that 

 of a mass two or three feet in diameter. The fault fissures 

 which we have observed to traverse the rock are either open 

 or are occupied by soft fault breccia, and have never been 

 filled by any infiltration of mineral matter from the adjacent 

 rock. Thost states, however (loc. cit., 123), that in some 

 cases they have served as receptacles for the more valuable 

 minerals. 



4. Ores, etc. — Copper pyrites (chalcopyrite) and grey 

 copper (kupferfahlerz) are the ores found in greatest quantity 

 at Tomnadashan. Iron pyrites accompanies them as usual, 

 being generally disseminated in cubes with alternately striated 

 sides and small pyritohedra, while thin plates and scales of 

 molybden glance are found in quartz veinlets traversing the 

 granitic rock, but so far as we know this mineral does not 

 occur in the basic rock at all. Silver ore is also stated to 

 have been found at Tomnadashan. The copper ore is prin- 

 cipally in the granitite which, when associated with any 

 considerable quantity of metalliferous mineral, is always 

 more or less decomposed — a circumstance often observed in 

 such deposits. 



Galena and zincblende, so often found along with these 

 ores, are quite foreign to this locality. 



Quartz, calcspar, and spathic iron are the chief accompany- 

 ing minerals, but barytes is also present in small quantities. 

 The sides of the old workings are coated with green malachite 

 and white stalactitic encrustations, one of which is crystallised 

 calcspar, and the other an amorphous sOicate. 



5. Mining History. — The ore was mined for nearly twenty 

 years before the death of the late Marquis, but no separate 

 returns of the output have been kept. 



A level was driven into the face of the hill above the 

 old smelting works to catch the supposed vein, but the ore, 

 as already indicated, is disseminated throughout the rock, and 

 the vein, having consequently no existence, was never reached. 

 Several vaulted cavities and small shafts sunk to the drift 



