20 Mr. Bryce on the altered Dolomites of the Island of Bute. 



formed by the mural precipices of the Causeway coast. It was shown that 

 this has been occasioned by a great fault, whereby the whole promontory 

 of Bengore, including the Causeway itself, and a tract of country five miles 

 long by one to one-and-a-half wide, has been thrown down about 400 feet, 

 and thus the upper beds of the superincumbent trap are brought to the same 

 level as the chalk. The same fault was shown to embrace also a portion 

 of the island of Kathlin. 



The various beds of the Causeway clifis were then described as rising 

 in succession from the sea level in Port- Moon, and attaining their highest 

 level in Pleaskin, whence they again descend in a long curve towards the 

 north of the Causeway, which is formed by the intersection of one of the 

 beds with the sea line. The beds rise again towards the west and run 

 out in succession, owing to the gradual lowering of the clifis. 



The beds forming the facades of Stafiia were next described, and were 

 shown to have a remarkable resemblance, both in mineral character, in 

 succession, and in thickness, to those of the Causeway. 



Some theoretical views were then stated respecting the origin of these 

 remarkable formations, and the former existence of separate volcanic 

 foci at the Giant's Causeway and Stafia, and on the probable connection 

 of these with movements of the surface still taking place along the great 

 Caledonian valley, and other lines parallel to the axis of the Grampian 

 chain. 



IV. — Note on the altered Dolomites of the Island of Bute. By James 

 Bryce, Jun., M.A., F.G.S. 



In the closing paragraphs of a paper on the geology of Bute, read 

 before the Society last session, and since published in their Journal, I 

 described certain changes which have been produced upon the Kilchattan 

 limestone by contact with igneous rocks. These changes, however, were 

 then but approximately determined, — the limestone having been subjected 

 by Mr. John Macadam, at my request, merely to a qualitative analysis, — 

 sufl&cient to indicate the character of the change, but of too general a 

 nature to ascertain the exact amount of change, as to afibrd definite terms 

 of comparison with the analyses of other limestones. Careful quantitative 

 analyses of a series of specimens have now been obtained through the 

 kindness of Dr. Robert D. Thomson ; — they have been made under his 

 care in the laboratory of the University ; and his name is a sufficient 

 guarantee for their accuracy. It is hoped that the publication of these 

 may lead to the formation of clearer views on an obscure question in 

 theoretic geology. 



The analyses kindly furnished to me by Dr. Robert D. Thomson, are 

 as follows : — 



Specimen No. 1, is the saccharine marble from the contact with the 

 dike at Kilchattan, in the highest state of alteration. It is the same as 

 No. 1 in Mr. Macadam's statement in my former paper. 



