110 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 9, 



or spike of crystals, varies more or less in size and modification. In 

 the small cavities containing these crystallizations, are associated 

 crystals of mby copper ; the latter never run out into spikes or 

 branching forms, but exist in single perfect or modified octahedrons, 

 or are dotted about in irregular clusters of crystals. 



The whole of these minute crystallizations occur in a bed of 

 brown limestone, yielding a soft, rich, yellow bisulphnret of copper, 

 — the rich ore, however, being very intimately mixed up with the 

 crystalline limestone, something like the material of a fine-grained 

 granite or porphyry. The ore contained in this bed seems to be a 

 medium or transition between the harder and more sulphureous ore 

 of the bed below and the carbonates and oxides of copper of the bed 

 above. The copper crystallizations here are peculiar to this bed 

 alone, and are doubtless the result of the decompositon of the ores 

 of copper. We observe that the ore of this bed is saturated with a 

 large quantity of moisture, which, if not the decomposiug agent, no 

 doubt facilitates the precipitation in these symmetrical forms. 



What seems also worthy of remark is, that all these minute cry- 

 stallizations of copper, whether ruby or metallic, have been formed 

 subsequently to the lime-crystals : these latter are often seen tipped 

 with an octahedron of ruby oxide, or overlaid with spikes of native 

 copper, as described ; but the lime never covers the different forms 

 of copper. 



Note by W. W. Smyth, Esq., Sec. G.S. — ^The minute arborescent crystals de- 

 scribed by Captain Vivian are very similar to those from Bogoslowsk in the Ural, 

 figured and explained by Grustavus Rose (Reise nach dem Ural, vol. i. p. 403). 

 These are twin-crystals, which group themselves in three directions parallel to 

 the three edges in which the cube-faces intersect one another in the common 

 plane of contact of the twin, thus forming angles of 120° with one another. 

 Subsidiary groups attach themselves to the above, in such wise that they form 

 angles of 60° with the three chief directions ; and, although the form is due to 

 the grouping of a great number of individuals, the parallehsm of their planes 

 gives the whole the character of one large compound crystal. — W. W. S. 



5. On the Slate-eocks and Teap-velns of Easdale and Oban. By 

 James Nicol, F.R.S.E., E.G.S., Professor of Natural History in 

 the University of Aberdeen. 



In the Geological Map of Scotland a narrow band of clay-slate is 

 laid down as skirting the eastern shore of Islay and Jura, and 

 passing through Luing and Seil to Kerrera and the vicinity of Oban. 

 This rock was fully described by Dr. Macculloch in his work on the 

 Western Isles ; and I should not have noticed it further, had not 

 my observations led me to differ from him in some important points. 

 My present remarks refer, however, only to this formation as seen 

 on Seil and Easdale and in the vinity of Oban, and more especially 

 to the former locality. This place has been long celebrated for its 

 extensive slate-quarries, the property of the Marquis of Breadalbane. 

 These works give employment to about 200 persons. They are 



