4.02 REPORT—1905. 
neighbourhood of Pretoria has thrown considerable light upon the structure of that 
area, and has shown how the strike of the Pretoria series and dolomite has been 
bent sharply to the south by the aid of a series of dislocations, sometimes nearly 
coinciding with the strike, and causing a repetition of the beds at the surface in a 
very striking manner. 
With regard to the series of the Waterberg sandstones—probably the equiva- 
len of the Matsap series of Stow in Griqualand West—the most important result 
of the work of the survey is the definite demonstration by Mr. E. T. Mellor of a 
decided unconformity between this series and the Pretoria beds, the evidence of 
which is very clear in the neighbourhood of Balmoral, east of Pretoria. It has 
further been shown that the red granite of the Bushveld is intrusive in and there- 
fore of later date than the Waterberg sandstone. Mr. Mellor’s more recent work 
to the north of the Eastern Railway line, on Rhenoster Kop, has shown that the 
deposition of the Waterberg sandstones was ushered in by manifestations of 
voleanic activity of very marked intensity, and that we must include in the lower 
portion of the series a considerable thickness of acid volcanic rocks, agglomerates, 
and conglomerates. 
With regard to the red granite and its associated acid and basic rocks, which 
cover such large areas in that portion of the Central Transvaal known as the 
Bushveld, these rocks and their principal variations have been studied by Mr. Halt 
and the author, and much evidence has been collected showing the intimate con- 
nection, in point of origin, between the various types. These constitute a petro- 
graphical province of considerable magnitude, and one which has played an 
important role in the geological history of the Transvaal. The whole complex, 
varying as it does from the acid red granites of the Bushveld to the pyroxenites, 
serpentines, and magnetite rock, which occur associated with the marginal belt of 
norites, forms another and striking example of differentiation from a parent magma, 
resulting on the whole in increasing basicity from centre to margin, and may not 
unreasonably be regarded as constituting a gigantic laccolitic intrusion, or series of 
intrusions, between the Pretoria and Waterberg series. The work of Mr. Hall has 
further considerably added to our knowledge of the nature and mode of occurrence 
of the cassiterite deposits of the Bushveld. 
Passing on to the Karroo system, a number of outliers of Karroo grits have 
been mapped to the north, north-east, and east of Pretoria, at the base of which 
beds of conglomerate, undoubtedly of glacial origin, frequently occur, corresponding 
in position to the well-known Dwyka conglomerate of Cape Colony. Associated 
with this deposit Mr. Mellor has recorded several excellent examples of glaciated 
land surfaces, considerably further north than any previously observed, and he has 
shown from the evidence of the glacial strize, which are very clearly marked, and 
from the character of the boulders in the conglomerate, that the general direction 
of ice-movement was from north to south. 
The pale fine-grained sandstones which border the Springbok flats have been 
shown by Mr. Mellor to be of Karroo age, and not to belong to the Waterberg 
series as previously supposed. These standstones overlie a series of grits seen near 
Pienaar’s River, and are overlain by the extensive flows of basic lavas—the so- 
called Bushveld amygdaloid—which constitute the central portion of the Springbok 
flats. It is interesting to note that a similar succession was found bythe author 
in a recent survey of the Karroo rocks of the eastern low country, in the neigh- 
bourhood of Komati Poort. 
The author concludes with a brief reference to the diamond pipes of the 
Pretoria district, with special reference to the included masses of Waterberg rocks 
in the Premier pipe, and the occurrence of hard blue ground, or ‘ hardibank,’ in 
the Schuller pipe. 
4. The Correlation between the pre-Karroo Beds of the Transvaal and 
those of the Cape Colony. By Dr. F, H. Harcu. 
The correlation of the pre-Karroo rocks of South Africa is a fascinating 
problem that has engaged the attention of most South African geologists at one 
