56 



NATURE 



[November 17, 1904 



volumes, the form of which, however unsuited to our 

 bookshelves, probably recalls to the Government 

 printers the blue-books of the old home-country. No 

 time has been lost, moreover, in the prosecution of 

 researches which furnish something' worthy to record, 



and the results have here been illustrated on an ex- 

 cellent and liberal scale. Topographic work has been 

 undertaken where e.xisting surveys are deficient, and 

 it seems probable that the geologists will run ahead, 

 for some years to come, of the accurate mapping of 

 the country. The beds dealt with are, firstly, the 

 Pretoria series of quartzites and 

 shales, which must have a high 

 antiquity ; secondly, the Waterberg 

 sandstones and grits, which are now 

 for the first time proved to be dis- 

 tinctly unconformable on the Pretoria 

 series ; and thirdly, the Karroo 

 system, or rather systems, which 

 opened under Glacial conditions, and 

 were laid down on the denuded sur- 

 face of the folded \^'aterberg series. 



The two earlier series are thus 

 clearly pre-Carboniferous. The Pre- 

 toria series is in places enormouslv 

 swollen by the intrusion of diabase, 

 which has worked its way along the 

 bedding-planes with remarkable regu- 

 larity. Where it breaks across the 

 beds, it becomes slightly modified and 

 charged with fragments from the 

 quartzites. The Waterberg series 

 near Balmoral has been invaded 

 laccolitically by a granite, which is 

 correlated with the red granite of the 

 northern Transvaal. On its upper 

 surface, which follows the planes of 

 stratification of the overlying beds, Fiu. 2.— Gi.^ciaieJ 

 it passes into a platy rock of the 

 compact quartz-porphyrv tvpe. 



Mr. E. T. Mellor regards the Waterberg series, with 

 its coarse breccias and conglomerates, as deposited in 

 waters swayed by powerful currents, torrents from the 

 land being responsible for the earlier beds. Frag- 

 ments of the Pretoria quartzites are found in these, 

 affording additional proof of the unconformitv (Fig. 1). 



NO. 1829, VOL. 71] 



The Karroo beds similarly contain boulders of the 

 rocks that preceded them, including the granite that » 

 rose beneath the Waterberg series. These boulders 

 occur in the Glacial beds at the base of the system, 

 corresponding with the Dwyka conglomerate of 

 Cape Colony. These beds were laid 

 down in a region already traversed 

 by large streams, and it is verv 

 interesting to note that the modern 

 Elands River, Bronkhorst Spruit, 

 and Wilge River have cleared the 

 Glacial beds out of the ancient 

 channels, and have followed in the 

 course of valleys that were long 

 fossilised and lost to view. 



.As in Cape Colony, the Lower 

 Karroo beds lie on handsomely glaci- 

 ated surfaces. Dr. Molengraaff 

 directed attention to these in 

 i.SjS, and Mr. Mellor has described 

 numerous new and admirable in 

 stances (Fig. 2). The uniform direc 

 tion of the stria from one exposure 

 to another points to an ice-sheet, and 

 not to local glaciers. The fact that 

 the movement was from north to 

 ~iiuth, speaking in general terms, 

 I' ith in the Transvaal and in Cape 

 ( \)lony, only adds zest to the search 

 for an explanation of this old 

 (ilacial epoch in the southern 

 hemisphere. It is satisfactory to 

 find that Dr. Molengraaff now con- 

 cludes that even in the Yryheid 

 district the ice-movement was from N.W. to S.E , 

 i.e., contrary to his previous suggestion. 



Mr. A. L. Hall found in the area allotted to him an 

 interesting series of igneous rocks, including a norite 

 which, near Onderstepoort, has given rise to consider- 

 able masses of inagnetite by a process of segregation. 



It is not so clear, however, that similar internal pro- 

 cesses, taking place during cooling, will account for 

 the passage of the norite into red granite, described as 

 occurring near the farm of Doornpoort. The facts 

 noted, particularly the mottling of the granite near its 

 margin, where it contains augite and decomposed 



