Vol. 50.] OF SOUTH- EASTERX AFKICA. 555 



The Dwyka Conglomerate continues in one unbroken line, from 

 St. John's River, through Pondohmd and Natal, to the Uuikuze 

 River in Zulnland ; it thins rapidly towards Swaziland; and near 

 the Pongolo River it dies away completely, disappearing at about 

 the same spot as the Ecca and Karoo Reds. 



The largest mass of foreign rock that I have found embedded in the 

 Dwyka Conglomerate was a boulder of granite, 9 feet long by 4 feet 

 wide, and protruding 3 feet above the matrix ; I do not know how 

 deep the boulder extended into it. In common with all the other 

 (smaller) boulders this was rounded at the angles, and showed con- 

 spicuous signs of having been submitted to severe aqueous action ; 

 but I could find no signs of any ice-action, either at this or any other 

 spot. I noticed one feature in the Dwyka Conglomerate in South- 

 eastern Africa which I have not seen hitherto mentioned, and that 

 was the occurrence of great intrusions and flat sheets of igneous rock 

 (dolerite), the latter either over- or underlying the conglomerate, and 

 sometimes both above and below. 



The controversy about the origin of the matrix of the Dwyka 

 Conglomerate has not, I believe, so far been definitely decided ; and 

 there appears to be as much evidence in favour of the igneous as of 

 the aqueous theory of the origin of the bulk of the rock. 



Dr. Gr. A. F. Molengraaf, Professor of Geology in the University 

 of Amsterdam, who has studied the rock both in situ and by means 

 of microscopic sections, expressed the following opinion of the origin 

 of the rock, in a letter to me, dated January 20th, 1892 : — 



" The Dwyka Conglomerate gives me the impression of a volcanic 

 tuff (I mean a probably Permian diabase-tuff), full of fragments of 

 older rocks. Such tuffs are not so very rare, even in diabases and 

 basalts themselves ; the amount of the different included rock-frag- 

 ments may surpass that of the rock itself." 



The masses of rounded rock and the numerous boulders and 

 pebble-beds contained in the Dwyka Conglomerate certainly point 

 to the fragments of other rocks contained therein having been sub- 

 mitted to the action of the ocean along a coast-line ; but might not 

 the material of the matrix here have been principally supplied from 

 some volcanic region now buried beneath a great mass of sedi- 

 mentary- strata ? 



So far all the strata dealt with have been approximately 

 horizontal, and no signs of unconformit)' exist inland. On the 

 coast, what there is of these beds, existing only in small isolated 

 patches along the sea-shore, is found to be dipping seaward ; a line 

 of hills, consisting principally of granite and Primary rocks, inter- 

 venes between this series on the coast and the same rocks inland. 



The Primary Rocks consist principally of: 



(8) Table-mountain Sandstone. 



This is found along the higher portions of the Roth as Hill range, 

 near Durban, where it lies horizontal and in small patches: and in 

 Zululand, principally near Ulundi. At this latter spot the series 



