408 REPORT—1905. 
striation. The best examples yet met with are those occurring to the north of 
the Douglas Colliery near Balmoral. In a number of examples distributed over 
an area of 300 square miles the strie exhibit great constancy of direction, and 
point to the existence of an extensive ice-sheet with a movement from N.N.W. 
to S.S.E. 
It is very probable that the glacial conglomerate extends very much further 
north than the localities at present known, During the past year outliers of the 
conglomerate were found ninety miles north of the latitude of Johannesburg. 
4. Note on the Occurrence of Dwyka Conglomerate at Kimberley Mine. 
By G. W. Lametucu, LBS. 
The author described the occurrence of glaciated boulders in the Dwyka con- 
glomerate and the cast of a glaviated surface, with striz running E, 30° N, in the 
open shaft of Kimberley mine. 
5. The Diamond Pipes and Fissures of South Africa. 
Ly Haroip §. Harcer. 
The author leads up to the subject of the formation of the diamond pipes and 
fissures by pointing out that for vast ages a great portion of South Africa was 
under water, during which period 14,000 feet of sediments were laid down, 
forming tke great Karroo system of fluviatile and lacustrine rocks. Their 
deposition was accompanied by a gradual subsidence or depression of the whole 
formation, during which faulting and fracturing of the earth’s crust occurred, 
assisting the infiltration of overlying waters and the generation of steam, and 
ultimately influencing widespread intrusions of basic, igneous rocks, such as 
dolorite and basalt. The whole series was afterwards raised again to its present 
level. At the close of the great period of immersion and deposition of sediments, 
violent quakes and explosions occurred, shattering the earth’s crust and facilitating 
the formation of volcanic rocks and huge fissures out of which issued enormous 
outpourings of amygdaloidal lavas, over 4,000 feet in thickness along the 
Drakensberg range. Following this period of activity came the intrusion of 
numerous volcanic pipes and fissures filled with the diamond-bearing ‘ blue ground ’ 
termed by Professor Carvill Lewis ‘ Kimberlite.’ This blue ground is a serpentine- 
breccia, and contains a larger number of minerals than any other known rock. 
The most prominent of these minerals are garnet, ilmenite, various pyroxenes, 
olivine, and mica, all of which are derived from the shattering to pieces of deep- 
seated ultra-basic and other rocks dissected by the pipe during the upward passage 
of the Kimberlite. The age of the pipes in the Cape Colony and O.R.C. is con- 
sidered by the author to be late Triassic or Jurassic, and the Pretoria pipes, for stated 
reasons, are contemporaneous. They are the latest eruptives of South Africa. 
The presence of many pipes on lines of weakness indicated by fissures filled with 
Kimberlite suggests that most of the pipes originated on fissures, and are there- 
fore closely associated with the Jatter. Both contain the same minerals and also 
diamonds, and their origin was due to the expansive force of great quantities of 
imprisoned vapour geverated at vast depths and liberated with sudden violence. 
The origin of the blue ground in the pipes he considered due to the shattering 
of the ultra-basic rocks such as eclogites, pyroxenites, and lherzolites, all of 
which are commonly met with, and are made up of the minerals which form the 
bulk of the blue ground. In these rocks garnet occurs plentifully, and also 
olivine and pyroxenes. The diamond has frequently been found crystallised in 
garnet, and more rarely in olivine ; hence the precious gem must have had its genesis * 
in the ultra-basis zone in which those minerals originated, The experiments of 
Sir William Crookes and of Moissan suggested that the presence of iron was 
necessary for the fermation of the diamond, but to this the author objects owing 
to the fact that the necessary iron does not exist in the diamond mines, and 
because Dr, Friedlinder’s experiments prove that diamond can be formed in 
