Dr. H. E.don — Geology of Ladysmith. 509 



(a) Tracliyte and tracby-audesite dykes. Most of these, occurring 

 about Broadford and in the Sleat district, seem to belong to a group 

 which has its chief ax'ea of distribution farther south-east, on the 

 Scottish mainland, and these rocks therefore cannot be attached to 

 the local series of the Skye focus. 



(6) Augite-andesite dykes, usually with glassy base, and other's 

 of acid pitchstone. Dykes and sills of these two rocks are more 

 numerous in the Isle of Arran, where, as Professor Judd has 

 shown, the two types are closely associated, sometimes in composite 

 intrusions. In Skye the known occurrences of acid pitchstone all 

 lie on a narrow belt passing through the granitic tract and having 

 a direction corresponding with that of the dykes themselves. They 

 thus seem to connect themselves with the Local Series as a final and 

 feeble recrudescence of activity about the acid Red Hills centre. 



The reversion in the closing stages to intermediate and finally to 

 acid types seems to suggest a new reversal of the order of eruptions, 

 and the composite intrusions (augite-andesite and acid pitchstone) of 

 Arran may perhaps be taken as pointing to a second critical epoch 

 during transitional conditions. These sporadic manifestations of an 

 igneous activity nearing its point of extinction do not, however, 

 afford any very firm ground for such deductions. 



VI. — Geological Notes on the Neighbourhood of Ladysmith, 



Natal. No. 1 : On some Igneous Rocks. 



By Dr. H. Exton, F.G.S. 



(Communicated by Professor T. Rupert Jones, F.R.S., F.G.S.) 



WRITING from the Station Hospital at Ladysmith, Dr. Henry 

 Exton, F.G.S., has communicated his observations on the 

 geology of the country near Ladysmith, in the northern part of 

 Natal, in letters to Professor T. Rupert Jones. A very noticeable 

 geological feature is the prevalence of an igneous rock (intrusive 

 andesitic diabase) on all the hills fi'om Umbulwana, four miles east 

 by south from Ladysmith, to the famed Spion Kop, sixteen miles 

 west from here. 



This rock covers all the hills, in rounded, smooth, and almost 

 polished boulder-like blocks, of a rusty brown hue on the surface, 

 with a clean blue crystalline fracture, and giving out a ringing 

 sound when struck. It is called by the Dutch yzad-Tclip (iron- 

 stone). The hill-sides around about here can be ascended on foot 

 only where a military road has been cleared to the summit. The 

 slopes of the hills are so profusely strewn with the rounded iron- 

 stone blocks that riding along them is impossible, and even walking 

 is a tedious task. The surface of the boulders is generally so rounded 

 and smooth that one has to tread between them, not upon them, 

 as the foot is apt to slide ofi". Of course, on the summits, where 

 these rocks are in mass, the rounding of the edges is not so apparent, 

 but they are alike weathered to a rich brown colour, very difl:erent 

 from the blue crystalline surface of a recent fractui'e. 



