Geological Society of London. 427 



was one of volcanic activity, apparently subaerial and terrestrial, 

 and representing the Lower Devonian. The Middle Devonian strata 

 consist of shales and sandstones devoid of any traces of volcanic 

 action, which, however, again becomes apparent in the UjDper De- 

 vonian. The latter consists of conglomerates, sandstones, and shales, 

 interstratified with aqueous deposits. The prevailing red colour 

 of these beds the author suggests may possibly indicate lacustrine 

 rather than marine conditions. 



The next in the series of deposits present in North Gippsland are 

 of Tertiary age, and rest horizontally on the flanks of tiie mountains 

 at elevations nowhere exceeding 1000 feet. At the close of the 

 Miocene and at the commencement of the Pliocene periods the land 

 probably was from 300 feet to 400 feet lower than at present. 



The fact that different genera of fish are found in the streams 

 flowing from the north and south sides of the Australian Alps 

 indicates the high antiquity of that watershed. These mountains 

 have been formed by the gradual elevation of the land en masse, and 

 its equally gradual erosion by the streams and rivers. 



16. " Further Notes on the Diamond Fields, etc., of South Africa." 

 By E. J. Dunn, Esq. Communicated by Prof. A. C. Eamsay, F.E.S. 



These notes are intended to serve as additions and corrections to 

 the author's paper read in 1873. 



Further mining operations at De Beer's show that the " pipes " 

 are more recent than the sheet of dolerite and other intrusive rocks 

 surrounding them. At this mine the only instance of a dyke 

 traversing the " pipe " occurs. Though the rock composing it was 

 too much decomposed to be determined, it was still quite distinct. 

 As the mines are worked out, they disclose a form less circular than 

 at first supposed. 



The first effect of the disruptive force was to cause a rent in the 

 rocks, the sides of which were afterwards torn away in the weaker 

 parts by the intrusive rock until the present form resulted. 



The ''cores or pipes" have decomposed downwards, being darker 

 coloured and less decomposed at 80 or 100 feet from the surface and 

 towards the centres. Several small freshwater shells were discovered 

 in Kimberley Mine, in an apparently undisturbed deposit. 



Gold is mined for at Leydenburg and Eersteling, in the Trans- 

 vaal Eepublic. The rocks in which it occurs are generally barren- 

 looking, and vary very much in strike. The alluvial gold at Leyden- 

 burgh as doubtless been supplied from two distinct sources ; it is 

 coarse and nuggetty as a rule, well rounded, and generally coated 

 with oxide of iron. Lumps up to 10 lbs. weight have been found; 

 it is of good quality, worth from 76 fr. to 80 fr. per oz. The auri- 

 ferous rocks at Eersteling are steatitic and chloritic schist resting 

 on gneiss, and overlain by rocks which at Leydenburg are auriferous. 



Cobalt is found near Oliphant Eiver, in fine-grained felsite rocks. 

 It does not occur in lodes, but in small threads and lenticular veins, 

 running parallel to a dyke of fine-grained dolerite. The widest 

 vein of ore was eight inches thick. More than 100 tons of ore have 

 been sent to London. 



(To be concluded in our next Xmnher.) 



