J. G. Goodchild — Scottish Copper-ores. 75 



To the first category belongs most of the Chalcopyrites occurring 

 in Scotland, and with that mineral is to be included also Chalcocite 

 and Bornite. These mostly occur in connection with mineral veins. 

 A small percentage of other compounds of Copper with Sulphur 

 appears to have originated in connection with certain eruptive rock 

 of sub-basic composition. When these latter have been affected by 

 dynamic metamorphism the process seems to have favoured the local 

 concentration of the mineral which was formerly diffused. Hence 

 several Epidiorites contain Chalcopyrites, apparently as an original 

 constituent (if we regard their schistosity as original to that type 

 of rock). 



To the second category, that of the ebb-products, or minerals of 

 secondary origin, belong all the remainder. 



Taking these in the order, and with the numbers, adopted by 

 Dana, we have, first, (15) Native Copper. There cannot be much 

 doubt that all the Scottish specimens of this are of secondary origin. 

 The earlier stage seems to have been that of solution, along with 

 those of the constituents of a sub-basic eruptive rock, through which, 

 probably, the copper ore was originally diffused in very minute 

 quantities. The decomposition of the rock by surface agencies has 

 again converted this into solution — probably in the form of carbonate 

 — from which solution any one of various reagents, in most cases 

 probably decomposing organic matter, has reduced the dissolved 

 substance to the metallic state. In this form it has been deposited 

 as thin sheets along the divisional planes of the rocks situated at 

 a lower level than its point of origin. In the form of films of this 

 kind it occurs at Boyleston, in Renfrewshire, where it is found in 

 lavas of Lower Carboniferous age ; and at Ballochmyle, in the joints 

 traversing the marls of the New Red Rocks there. I may remark, 

 in passing, that these rocks so closely resemble the Bunter Sandstone 

 that I should never have hesitated to refer them to that horizon had 

 not a different opinion regarding their age been expressed by the- 

 distinguished author of " The Scenery of Scotland." 



Native Copper also occurs in the form of minute particles — 

 possibly crystals — in some of the Prehnites of Boyleston and Glen 

 Farg. Doubtless these varieties of Prehnite owe their colouring 

 matter to the presence of this mineral, just as the ordinary green 

 variety of Prehnite owes its colour to diffused compounds of copper 

 of other kinds — possibly to Chrysocolla. The same metal also 

 occurs at Boyleston, disseminated throughout some of the beautiful 

 crystals of Calcite which line some of the drusy cavities of the lavas 

 there. When Native Copper is enclosed in these crystals the 

 external form is much more complex than where the metal is absent. 



Some Chalcopyrites must undoubtedly be classed amongst ebb- 

 products also, seeing that a second generation of crystals often occurs 

 upon minerals whose secondary origin cannot be doubted. Atacamite 

 has been claimed as a Scottish mineral, but, it seems to me, on 

 insufficient grounds. 



(224) Cuprite, as might be expected, occurs in connection with 

 the other decomposition products of common ores. Usually it occurs 



