68 Transactions of the South African Philosophical Society. 
bench mark ; below its main body it is useless to search for coal, 
but above it, either directly or in some cases perhaps at a con- 
siderable height above it (because the conglomerate was in places 
unevenly deposited, and was probably levelled up before the coal 
seam was deposited), the coal measures and coal were laid down. 
North of Kimberley the Dwyka conglomerate is exposed, and near 
the Vaal River again on the south bank at varying distances up to 
Parys in the Free State, then it turns northward, passing 2 miles 
south of Meyerton Station, and again crosses the Vaal to the south 
bank a little east of Vereeniging, continues along the Vaal River 
until south of Heidelberg, where it encloses the South Rand coal- 
field on the north side of the Vaal, as shown on Mr. Sawyer’s 
geological plan of that area, turns south and crosses the Vaal River 
into the Free State, then turns northward and passes a few miles 
east of Heidelberg, Transvaal, and on to the Wilge River, then turns 
easterly and passes to the south of Middelberg, turns up towards 
Steenkamp’s Berg, and thence runs south-easterly along the east slope 
of the Drakensberg, past the Slangapies Berg and southward through 
Zululand to the junction of the Mooi and Tugela Rivers in Natal. 
This gives a total length of the area occupied by the Dwyka con- 
glomerate and its accompanying coal measures of 800 miles from 
Middleberg, Transvaal, to near Karroo Poort, Cape Colony, and an 
extreme width of 350 miles between Kimberley and Hast London. 
Outside of this area outliers occur at many places, the Zyferfontein 
and Boksberg coal-fields in the Transvaal belonging to this same 
horizon, and east of Boksberg undisturbed Dwyka conglomerate 
exists, while the denuded material from the conglomerate covers 
considerable areas of the older rocks on the north side of the Vaal 
River. 
The length of the outcrop of the Dwyka conglomerate and accom- 
panying black shales, coal, &c., exceeds 2,000 miles. In 1886 the 
black shales and other strong indications of coal, and in places thin 
seams of coal, also were known. Now with the light thrown on the 
subject by the Vereeniging and other extensive coal-mines along the 
northern edge of the area, the argument formerly advanced that the 
poverty of the outcrop in coal argued against coal in quantity exist- 
ing in workable seams further into the basin falls completely to the 
ground, for such coal seams as are now being worked within the 
northern rim of the area are simply phenomenal, ranging for 6 feet 
of workable coal to over 60 feet. 
In 1886 the probability of Sub-Karroo coal was predicted on 
geological grounds alone. The realisation far exceeds the most 
sanguine expectations, for at the horizon indicated excellent coal in 
