Geological Society of London. 329 



the relation of their distribution to the former extension and effects 

 of ice in the Lake District. He briefly noticed the occurrence of 

 additional boulders of picrite in Anglesey, and described specimens 

 from two localities (Caemawr and Pengorphwysfa) where a similar 

 rock has been discovered in situ by Professor Hughes. Hence it is 

 probable that the Anglesey boulders are derived from localities in 

 that island, and not from Cumberland. From a re-examination of 

 specimens collected by the late Professor Sedgwick and Mr. Tawney, 

 preserved in the Woodwardian Museum at Cambridge, the author 

 showed that the rock must occur in situ in two localities in the Lleyn 

 peninsula, in the neighbourhood of Clynnog and of Aberdaron. 

 Lastly, he described a very remarkable picrite boulder, discovered 

 by Dr. Hicks, which rests on " Dimetian " rock at Porthlisky near 

 St. Davids. 



2. " Sketches of South-African Geology. — No. 2. A Sketch of the 

 Gold-Fields of the Transvaal, South Africa." By W. H. Penning, 

 Esq., F.G.S. 



The Gold-Fields of the Transvaal have been defined as covering 

 nearly all the eastern and northern districts of the State, though but 

 a small portion of the area is productive. In this paper the author 

 described only the Lydenburg and De Kaap gold-fields, leaving those 

 of Pretoria and Mai-abastadt for a future communication. The 

 auriferous region is known to extend 350 miles to the northward 

 beyond the Limpopo river, so that the gold-bearing rocks are found 

 throughout at least 7^ degrees of latitude and 3 of longitude. 



The area of the two gold-fields mentioned, comprising together 

 about 3000 square miles, was defined ; and the author, after noticing 

 some old gold- workings, proceeded to give an account of the physical 

 features of the country. He especially called attention to the cir- 

 cumstance that most of the rivers rise to the west of the highest 

 range, and flow eastward through it. 



The oldest gold-bearing rocks consist of unfossiliferous schists, 

 shales, cherts, and quartzites, classed by the author as Silurian. 

 Amongst these a great mass of coarse granitic rock is intruded, con- 

 sisting of quartz and felspar, with but little, if any, mica. This 

 granite, in the De Kaap valley, forms an ellipse 17 miles long by 

 10 broad, with a narrow northerly prolongation. Both the granite 

 and the stratified rock are traversed by intrusive dykes, chiefly of 

 diorite. 



These beds have been much disturbed, and then cut down, pro- 

 bably by marine denudation, to a level plain 1700 or 1800 feet above 

 the sea. Upon them rest unconformably a great sequence of con- 

 glomerates, sandstones, and shales, the " Megaliesberg beds " of a 

 former paper, but now provisionally classed as Devonian. These 

 rocks also are traversed by dykes of diorite and other kinds of trap. 

 The "High Veldt beds " overlie the " Devonian " with some uncon- 

 formity. 



Several sections and observations illustrative of these facts were 

 described, and details were given of the different gold-mines in each 

 of the great systems noticed, and also in alluvial deposits. It was 



