Age of the Altered Limestone of Strath, Skye. 73 



along the railway, further west, and on those supplied to him from 

 near Lake Huron by Dr. Selwyn. As a rule these are but little 

 altered. Some contain fragments of igneous rocks, apparently 

 lavas. 



The author discusses the significance of the changes in these 

 rocks, as bearing on general questions of metamorphism, and states 

 that, in his opinion, the name Huronian, at present, includes either 

 a series of such great thickness that the lower beds are more highly 

 altered than the higher, or else two distinct series ; and he inclines 

 to the latter view. Both, however, must be separated from the 

 Laurentian by a great interval of time, and neither exhibits meta- 

 morphism comparable with that of a series of schists and gneisses, 

 like the so-called Montalban. The newer reminds him often of the 

 English Pebidians. 



December 7. — Prof. J. W. Judd, F.E.S., President, in the Chair. 



The following communications were read : — 



1. " A Letter from ELM. Secretary of State for the Colonies, 

 enclosing an account of recent Discoveries of Gold in the Trans- 

 vaal." 



The deposits in which gold has been found, locally known as 

 "banket," consist of a quartz-conglomerate forming so-called "reefs," 

 which traverse the veldt parallel to, but at a short distance from, 

 the rocky ridge of Witwatersrand. These masses always dip to the 

 south, but at angles varying from 30° up to 90°. The " reefs " are 

 believed to have been discovered by Mr. Struben, an English gentle- 

 man long resident in the country. The " main reef " has been traced 

 for twenty-five or thirty miles, and varies in breadth from 3 feet 

 6 inches to 15 feet ; parallel and branching " reefs " of smaller 

 dimensions have also been found. The yield of gold is said to be 

 very variable in different portions of the " reef," different samples 

 with from 3 oz. to | oz. per ton occurring in close proximity. So 

 far as observation has gone (and the deepest workings have only 

 reached a depth of from 70 to 150 feet), the yield of gold has gene- 

 rally increased as the reefs are followed downwards. 



2. " On the Age of the Altered Limestone of Strath, Skye." By 

 Dr. Archibald Geikie, E.R.S., Y.P.G.S. 



The remarkable alteration of the limestone of Strath into a 

 white saccharoid marble, first described by Macculloch, has hitherto 

 been regarded as an instance of contact-metamorphism in a rock of 

 Liassic age. The various writers who have described the geology 

 of the district have followed Macculloch in classing the whole of the 

 ordinary and altered limestone with the Secondary series of the 

 Inner Hebrides. The author, however, saw reason in 1861 to sus- 

 pect that some part of the limestone must be of the age of the 

 Durness Limestone of Sutherland, that is, Lower Silurian ; and he 

 expressed this suspicion in a joint paper by the late Sir Ii. I. Mur- 

 chison and himself, published in the 18th volume of the Quarterly 

 Journal of the Society. He has recently returned to the subject, 



