INTERESTING CONTACT OF DOLERITE WITH SANDSTONE. 393 



Note on an Interesting Contact of Dolerite with 

 Sandstone from the Ecca Beds of Elandslaagte, 

 Natal. 



By 

 F. H. Hatch, Ph.D., F.G.S. M.Iiist.C'.E., 



Vice-President of the Institution of Mining and Metallurgy, and Past- 

 President of tlie Geological Society of South Africa. 



With Plate XXXI. 



The specimens showing the contact here to be described 

 were handed by Dr. Warren, of the Natal Museum, to the 

 author during his visit to Natal in 1909. They are pieces 

 of the core from a bore-hole at Elandslaagte, Natal, which 

 intersected a sill of compact dolerite, eleven feet thick, travers- 

 ing Ecca Beds, the upper junction being at 109 feet from the 

 surface, the lower at 120. 'Thin sections of both junctions were 

 made, and these, in both cases, show unmistakable evidence 

 of the thermal changes due to contact, so that it is clearly 

 evident that this is an intrusive sill and not a flow. 



Thi<] Sandstone. 



A hand specimen of this rock shows it to be particularly 

 fine-grained and compact, the component particles being 

 scarcely discernible without the aid of a lens. Under the 

 microscope it is found to consist mainly of sub-angular grains 

 of quartz with subordinate striated felspar, flakes of biotite 

 and isolated particles of garnet, all embedded in a carbonate 

 cement, which, judging by its appearance and faint brown 

 colour, probably consists of carbonates of lime, iron, and 

 magnesia. 



