238 Reports and Proceedings — Geological Societg of London. 



wliicb they were originally included. Minute crystals, referred to 

 as ' microlithic needles,' resemble 'clay-slate needles,' but are not 

 always straight : tbey occur in every fine residue, and as inclusions 

 in siliceous and micaceous flakes. The siliceous fragments which 

 enclose them frequently contain many liquid inclusions, which does 

 not necessarily imply any connexion between the two, though there 

 may possibly be some connexion. Micro-crystals of quartz occur, 

 and have been derived from decomposing silicates. 



II.— April 6, 1892.— W. H. Hudleston, Esq., M.A., F.R.S., 

 President, in the Chair. — The following communications were read : 



1. "Geology of the Gold-bearing Rocks of the Southern Trans- 

 vaal." By Walcot Gibson, Esq., F.G.S. 



The author describes the general characteristics of the rocks of 

 the Southern Transvaal, and gives a summary of previous work on 

 the area ; he then discusses the physical relations of the gold- 

 bearing conglomerates and associated rocks in the Witwatersrandt 

 district, and describes the various rocks in detail. 



He concludes that the gold-bearing conglomerates and the 

 quartzites and shales of the Witwatersrandt district (which have 

 undergone considerable metauiorphism) form one series, of which 

 the base and summit are not seen : that this series is much newer 

 than the gneisses and granites on the eroded edges of which they 

 rest, and older than the coal-bearing beds which unconformably 

 overlie them ; that the entire series associated with the gold-bearing 

 beds has been thrust over the gneisses, and was not originally 

 deposited in its present position, the movements having taken place 

 in two directions, viz. from south to north and fi-om east to west; 

 that, after the cessation of these movements, the strata were injected 

 with basic and sub-basic igneous material, and much of the country 

 was flooded with lavas of the same character ; and that the con- 

 glomerates have been formed mainly at the expense of the under- 

 lying granites, and gneisses which were largely threaded with 

 auriferous quartz-veins and contained larger masses of quartz. 



The author then describes the geology of districts outside the 

 typical area, which, though at first sight more complex, are really 

 simpler than that of the typical area. The conclusions arrived at 

 from an examination of these areas confirm the results of the study 

 of the rocks of the Witwatersrandt district. 



2. "The Precipitation and Deposition of Sea-borne Sediment." 

 By R. G. Mackley Browne, Esq., F.G.S. 



The author discusses the mode of deposition of current-borne 

 sediment upon the ocean-floors, and considers the effects of current- 

 action in sifting the material and causing it to accumulate into 

 stratified linear ridges having directions generally parallel with 

 those of the currents — the dip of the strata varying according to the 

 velocity of the currents. He considers that the conclusions deducible 

 from his analysis appear to be in accord with the evidence afforded 

 by the structure of ancient subaqueous sedimentary deposits. 



