ALTERED LIMESTONE OF STRATH, SKYE, 73 



Besides the protrusions of granophyre, innumerable basalt-dykes, 

 likewise of Tertiary age, traverse the Silurian limestone, as well as 

 all the other rocks of the district. The amount of alteration they 

 have effected is trifling, notwithstanding their number and the pro- 

 longed period during which they continued to be injected into fis- 

 sures in the rocks. They began to be formed before the appearance 

 of the granophyres which cut them off and send veins into them ; 

 but their extravasation was afterwards resumed, for some of them 

 are found running across the bosses of granophyre. It is not to 

 the intrusion of the basic dykes, but to the uprise of the bosses of 

 eruptive acid rocks that the Lower Silurian Limestone of Strath owes 

 the metamorphism which has made it famous. 



Discussion. 



The President expressed his satisfaction at the lucid explanation 

 of the old problem offered by Dr. Geikie. He had himself fallen 

 into the same error as others with regard to the passage of Lias 

 limestone into white marble in Skye. 



Mr. Etheridge pointed out the close resemblance of the species 

 exhibited from Durness and Skye. He also specially called atten- 

 tion to some of the fossils exhibited. 



Dr. Hicks agreed that the similarity between the Durness and 

 Skye limestones was unmistakable ; the latter appeared to be the 

 same as the lower beds of Durness. There was very little change 

 in the general sequence throughout the west coast of N. Scotland. 



Mr. Marr observed that the Durness Limestone is precisely similar 

 to the widely spread Orthoce7'as-\im.esione of Sweden and the Stin- 

 char limestone of Girvan, so the occurrence of the same formation 

 in Skye is natural. It was to be hoped that as rich a fauna 

 would be found in Scotland as in Scandinavia. 



Dr. HiNDE pointed out the similarity of the fossils from Durness 

 and Skye to those described by Billings from the Calciferous Lime- 

 stones of the Mingan Islands, on the north shore of the St. 

 Lawrence. Amongst others, the doubtful genus Arcliceocyatlms is 

 present at Mingan, at Newfoundland, and at Durness, and in all 

 these localities it is associated with similar forms of lladurea, 

 Murchisonia, &c. 



Mr. Bauerman had seen limestones in Matto Grosso, in Brazil, 

 containing peculiar aggregations of quartz somewhat resembling 

 fossils, and similar rocks were found in the province of S. Paulo, 

 about 700 miles distant from the first locality. The latter were 

 considered to be of Huronian age. 



The President expressed a hope that full details of the Durness 

 Limestone and its fossils would be published before long. 



Dr. Geikie thanked the Fellows for the reception they had given 

 to his paper. A preliminary sketch of the results of the recent work 

 of the Geological Survey in the north-west of Scotland would, he 

 hoped, be presented to the Society early next year. 



