136 Geological Society : — 



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 from 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 eftects 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. 



April 27.— Prof. J. W. Judd, F.R.S., Vice-President, 

 in the Chair. 



Prof. "W. C. Williamson, F.R.S., exhibited the following spe- 

 cimens : — 



Slab of Carboniferous Limestone from Bolland, illustrating the 

 passage of a foraminiferal ooze into crystalline calcite ; 



Asteropecten Orion, Forbes, from the Kellaways Rock, near 

 Pickering, Yorkshire : 

 and made the following remarks : — 



The specimen before me is a slab of Carboniferous Limestone 

 from the Bolland district of West Yorkshire. In its centre is 

 a magnificent section of a large Nautilus — beautiful as a fossil, but 

 still more important because of what it teaches. Its large terminal 

 chamber is filled with foraminiferal ooze, the component objects 

 of which are almost as perfect as when the organisms were living. 

 The surrounding limestone is chiefly in an amorphous state ; but it 

 contains innumerable evidences that it also consists of foraminiferal 

 ooze, largely reduced to the amorphous state by the agency of car- 

 bonic acid, now known to be so abundant in the depths of the 

 ocean. The action of this acid upon the minute calcareous shells 

 necessarily converted the water into a solution of carbonate of 

 lime. In this state it percolated by osmosis through the shell of 

 the Nautilus, penetrating its closed chambers, which it gradually 



