254 



PEOF. A. H. GEEEN ON THE aEOLOGT AlfD 



Further details about the Eed Beds, the Cave Sandstone, and the 

 Volcanic Beds will be found in Mr. Dunn's Report on the Stormbergen 

 Coalfields (Cape Town, 1878). 



Intrusive and Contemporaneous Traps. — The whole of the country 

 occupied by the Kimberley Shales and the Karoo and Stormberg 

 Beds is seamed with almost innumerable dykes and intrusive sheets 

 of trap. They are thicker in some quarters than in others, but you 

 cannot move far anywhere without coming across more or less of 

 them. The following, which I have examined microscopically, 

 seem all very similar in character *. 



Intrusive Sheet, at the Reservoir, Beaufort West. Thick Sheet, 

 Colesherg. — An interlacing mass of lath-shaped crystals of plagioclase 

 (•2 to "3 millim. across) and augite ; little olivine ; ilmenite ; very 

 fresh. The felspar crystals penetrate the augite, but hardly to such 

 an extent as to produce marked ophitic structure. 



Sheet on top of HangTclip f, near Queenstown. — Very marked ophitic 

 structure ; broad plates of augite penetrated by lath-shaped crystals 

 of plagioclase (-07 millim. across). Granules of olivine, some en- 

 closed in the augite ; little ilmenite ; very fresh. 



The rock is columnar, and the base of the sheet clearly cuts across 

 the bedding of the shales on which it rests. 



Intrusive Sheet, Dordrecht, — Exactly like the last ; plagioclase 

 laths 1'7 to '8 millim. across. 



East of Vet River, Whiburg, Orange Free State. — Very similar to 

 the last two ; olivine somewhat decomposed ; plagioclase laths -3 to 

 •5 millim. across. 



Sheet at top of the Be Beer's Mine, Kimherley. — Laths of plagio- 

 clase, •! to -5 millim. across ; olivine; ilmenite; felspar penetrates 

 both augite and olivine ; some olivine enclosed in the augite. 



Sheet 071 slope of Hanghlip, near Queenstown. — About three 

 quarters of the slice is occupied by laths of plagioclase, '01 to '03 

 millim. across, with ragged, ill-defined boundaries. The spaces 

 iietween are filled in with a green fibrous decomposition-product, in 

 which comparatively unaltered augite and olivine can be detected 

 here and there. 



Thich Sheet in Kimherley Mine. — Laths of plagioclase '05 to '1 

 millim. across ; viridite and opacite ; plagioclase penetrates the 

 other constituents. It is not clear what minerals have given rise 

 to the decomposition-products. If these were augite and olivine, 

 the rock must have been originally very similar to that last described. 



Spheroidal and columnar structures are common in these traps. 

 Some of them also show in a very marked way curvi-tabular struc- 

 ture ; the rock is traversed by curved planes of division, running 

 parallel to each other, the weathered surface is commonly formed 

 by one of these curved surfaces, and we have along the outcrop a 

 series of bosses with gently rounded tops, which bear a considerable 

 resemblance to roches moutonnees. It looked in some cases as if 

 the intrusion of the trap had bent up the overlying beds into a flat 



* For further details and analyses see Dr. Cohen's paper already quoted, 

 t Quart. Journ, Geol. Soc. vol. xxvii. (1871), p. 531. 



