UNION OF SOUTH AFRICA. GEOLOGICAL.sURVEY OF PORTION OF THE COUNTRY EAST OF STEYTLERVILLE, Cape. Province

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1 UNION OF SOUTH AFRICA DEPARTMENT OF MINES GEOLOGICAL.sURVEY THE GEOLOGY OF PORTION OF THE COUNTRY EAST OF STEYTLERVILLE, Cape. Province An Explanation of Sheet No. 150 (Sundays River) BY S. H. HAUGHTON, B.A., D.Se., F.G.S. WITH A CHAPTER ON UNDERGROUND WATER RESOURCES BY H. F. FROMMURZE, B.Sc. Published by Authority 0/ ih.e HonQurable the Mim'sier 0/ Mines Price: 5,. (including map) [COYPRWHT] THE (jovernment PRINTER, PRETORIA 1935 G.P. S / 5/35-1,000.

2 26 2. Intermediate Gravels. West of Sundays Wver poort, from about the middle of Schietnek westwards to Sapkamma (B-3), there is a well-defined terrace flanking the southern escarpment of the Klein Winterhoek range at a height of 850-goo feet above sea-level. The surface of this terrace is covered with a layer of unconsolidated gravel. The terrace slopes gradually up to the sides of the Witte berg hills; but its southern edge forms a fairly abrupt scarp. The flat top is dissected by numerous small streams. In addition to the predominant quartzite boulders, the gravel contains boulders of breccia-conglomerate (possibly derived from Enon beds), one or two small pieces of tillite, and occasional pieces of calcareous tufa. Gravels at approximately the same height occur at severallocalities on the south side of the Kariega valley. On Schuilpatdop and Lower Krompoort (B-3) flat-topped ridges are capped with a layer of coarse gravel composed of quartzite boulders and pebbles and angular but slightly worn fragments of dark grey Bokkeveld sandstone. A similar but larger remnant of gravel-covered terrace occurs on Toverklip (B-3). Here the gravel is mixed with calcareous tufa, which is also found in the light sandy soil of the lower ground. At Bacot Pile and for some distance north-east of it along the Toverklip-Brandt Koppen boundary gravels occur at a greater height above sea-level than those to the east of Adolphspoort. They may represent a stage intermediate between those of Brandskop and those of Toverklip; but on the map they are indicated by the same sign as the latter. 3. AUu.vium and Recent Gravels. The largest stretch of alluvium in the area occurs in the valley of the Sundays River below Courans Drift. This alluvial plain forms the only region of closely-settled land in the area. Narrow patches on the inner sides of the meanders of the Kariega H.iver on Kariega and at the lower ends of Krompoort and Adolphspoort are also cultivated. Stretches of alluvium also occur along the banks of the spruits in the Springbok Vlackte; but here the alluvial soils seem to be poor. Within the valley of the Kariega, particularly within a few miles of its junction with the Sundays I<iver, are flat plains covered with fine gravel and calcareous tufa. VII.-THE UNDERGR.OUND WATEI~ RESOUlZCES. By H. F. FIlOMMUIlZE, B.Sc. I. Introduction. 2. Artesian Areas. The Sundays River Valley and its western extension. 3. Bormg for water for domestic and stock purposes,,~shallow supplies. r. INTIlODUCTION. With the exception of a few square miles of alluvium at the village of Kirkwood in the south eastern corner of the sheet which are irrigated by the waters of Lake Mentz, the whole of this area is occupied by farmers of small stock.

3 To these pastoralists supplies of fresh water, not necessarily great in quantity, are of great importance. Particularly is this so as the modern practice of dividing the farm into separate camps supersedes herding and kraaling.. Thus the members of a rural community of this nature in this type of country where perennial water is very scarce are dependent entirely for their domestic and stock water supplies on the conservation of storm waters and the tapping of underground reservoirs by boring. Boring for water in this area has been tried by many, but the yields have proved low, and generally the water is of such a saline nature that it has not been possible to use it. Especially is this so in the southern portion of the sheet where the Bokkeveld and Cretaceous beds south of the Klein Winterhoek and the Zuurberg form the subsurface rocks. The degree of mineralisation of these waters has proved so bad that in many localities the farmers have abmldoned these sources of supply and are relying entirely on small dams for their water. This fact is very noticeable in the area which is underlain by the Cretaceous beds. 2. THE ARTESIAN AREA. A.-The Sundays River Valley. Du Toit says" The synclinal structure of this area is certainly conductive to artesian conditions, but the great thickness attained by the cover will involve deep boring while the quality of the supply is in some doubt. The seal would be formed by the blue and grey clays and sandy shales of the Marine Beds, while the water-bearing division would be constituted by the underlying series of yellow soft sandstones, interbedded with mudstones and red and green clays belonging to the Wood Beds and Variegated Marls. Owing to the high dip away from the Zuurberg, the Enon Series, which is the waterbearer to the southwest, plunges too deeply to be reached anywhere at points more than a few miles to the south of its outcrop along the foothills of this range, but boring could be done in the narrow belt from Kirkwood to the East. The main intake of the basin would be situated within the Coerney Valley chiefly where tlie altitudes of the ground are by no means great, and consequently the pressures to be expected could not be high." He does not think that the water would rise above the surface except in the. lower part of the valley, and further he considers that the depth of the aquifer below the. surface will be excessive except along the northern and southern margins of the basin. It is thought that this basin structure continues westwards and that it may be possible to make use of the northern section as far as Courans Drift (B-4' and the lower portions of the Kariega River valley, particularly the narrow strip just south of the great fault. * Du Toit A,L. The Underground Water Resources of the Uitenhagc Region. Explanation of Cape Sheet 9 (Port Elizabeth).

4 23. B.-The Kariega River Valley. (See Section C-D on map.) Westwards to the postulated N -S fault on Roodekrans and Rhinoster Hoek NO.2 (B-21 against which the rocks of the Stormberg Series terminate it is possible that water in sufficient quantities may be obtained by drilling into the Variegatcd Marls and Wood beds of the Uitenhage Serics though it would be necessary to go to great depths (over 3,000 feet) in the central portion of the basin. The marginal portions would be more favourable particularly the northern edge. The great difficulty here would be the quality of the water as these strata are notorious for the salt water which they carry, and on the southern edge they are underlain by the Bokkeveld slates which also carry salt water 'The great depths to,vhieh it \~'ould be necessary' to drill. and the probability that the water would not flow over the surface except in limited areas, tend to makc any operations for the development of these waters of doubtful economic value. C.-The Western end of the Basin. (See Section A-B on map.) This portion extends from the hidden fault up to Eerenkroons (13-I). Here the structure differs slightly as the basin is lined with the sediments, lavas and tufis of the Stormberg series and filled with conglomerates and sandstones of Enon age. The Enon beds and the lavas, the latter especially when decomposed, are porous and make excellent aquifers. Below these porous strata are the impervious clays and marls which constitute the Stormberg sediments, to act as a basal impervious layer. The basin would. be fed from the run-off from the hard Witteberg ranges to the north which finds its way along the drainage lines formed by the tributaries of the Groot River. The artesian conditions are not so favourable as those further east as there is the possibility of the water leaking through the fault into the Marine and \Vood beds to the east, and as in other places there is mnch doubt concerning the quality of the water. There is no evidence as to what sort of water will be obtained from the Stormberg beds, but most of the shallow supplies in the Enon in the area in question have a high degree of brackness. POSSibly here as further east if it is ever decided to test the underground water-bearing properties of this structure it might be as well to place any bores on the northern margin before attempting any operations in the centre or south. 3. BORING FOR WATER FOl( DO~lEimc AND STOCK SUPPLIES. r; The Cretaceous System. The outstanding feature of the boring operations in these rocks is the salinity of the water obtained, fifty per cent. of the holes being reported as producing salt water.* * A. L. du Toit: Borehole V-later Supplies in the Union of South Africa. Trans. " Dd the Minutes of Proceedings of the S. Ai. Soc. of Civil Engineers, 1928.

5 29 (a) Average results from the Marine Beds (Grey and Green Clays with fossiliferous patches).. (b) (e) Number of boreholes from which iiifonll<ltion was gathered.... Average depth of boreholes -in feet...,... '".... Average depth at which water was struck in feet,......,..., A veragco nepth to which wat.er rises (rest level) in feet. Average daily yield in gallons pumping.,.... Percentage of supplies which "are brack... '...,...,,.... Average results from the Variegated Marls and Wood Beds. 22 I95- ' XI, Number of boreholes from which information was gathered.,. 31 Average depth of boreholes in feet... ' r80 Average depth at which water was struck in feet.... IZI Average depth to which water rises (rest level) in feet"",""'" 51 A veragc daily yield in gallons pumping,,, ',, ', ',',,,..,..., ' 10,000 Percentage of supplies which arc brack,,,,..,.,. '... ' 64 Average results from the E1Ion Beds. Number of boreholes from which information was gathered, 5 Average depth of borehole in feet,...,..,, :, ',,..,. ',... ', Average depth. at which water was struck in feet,, ',,..,..., Average depth to which water rises (rest level) in feet,., Average daily yield in gallons pumping..., ,000 Percentage of supplies which are brack.,..,,..,...,...,. 20 As will be seen there is a similarity between the first two divisions but in the third the daily average is low but the quality is better. Z. The Karroo System, (al The Stormberg Series.-The outcrops of this series of rocks occupy a very restricted area and no results have been obtained up to date. (b) The Eeea Series.-The greater portion of the area north of the Klein Winterhoek and the Zuurbergen is underlain by the shales and sandstones of this series. The folding which has taken place has resulted in some of the rocks becoming highly tilted, which condition is favourable for obtaining supplies uf underground water, especially along 'the natural drainage lines where replenishment of supplies takes place. The following average results have been obtained from boreholes: Number of boreholcs from which information was obtained. 26 Average total depth of borehole in feet. '.,,...,,. ' Average depth at which water was struck in feet. go Average depth to which water rises (rest leverl in feet.,.,,., Average daily yield in gallons pumping...,...,.,..., 12,000 Percentage of failures.,.,..,...,,..,,.,...,.,,. '...,, 24 The quality of the water obtained is always doubtful as in this area it is always more or less mineralised. The question as to whether the supply will be potable or not depends upon the degree of mineralization of the water. A high degree of variation in the salinity takes place within a short distance, In the absence of dolerite sheet and dyke intrusions it is advisable to confine the selection of sites to positions along the drainage lines, and to make use of the alternating hard and soft layers in this series.

30 3. The Dwyka Series. Similar results to those obtained in the Ecca are obtained in this series, but the degree of salinity is generally higher. 4. The Cape System. Witteberg Series.

6 30 3. The Dwyka Series. Similar results to those obtained in the Ecca are obtained in this series, but the degree of salinity is generally higher. 4. The Cape System. Witteberg Series.-Not much boring for water has taken place in this area in these highly tilted and folded quartzites and slates as they form mountain ranges or the" ribs of the folded belt," as mentioned before. If advantage be taken of the softer zones in this series the tilted and jointed nature of the rocks shonld prove favourable for furnishing underground supplies of water as at Glenconnor where the Eailways have sunk a hole in the Witte berg on rising ground which delivers a quantity of water reported as 200,000 gallons per diem. The Bokkeveld Series.--This series is composed predominantly of shales and slates which are often highly tilted and cleaved, and covered as they are by sparse occurrences of thin soil, there is nothing to stop infiltration of meteoric waters. A consideration of the boring results however shows low average yields of brackish water. The low results obtained are due probably to the highly dissected nature of the country and the low average annual rainfall. Number of boreholes from which information was obtained. Total average depth of borehole in feet.... Average depth at which water was struck in feet. Average depth to which water rises (rest level) in fect... Average daily yield in gallons pumping.,.... Percentage of brack supplies roo , In general, however, the supplies yielded per borehole are low, and salt waters can be expected everywhere with the exception of those from the Witteberg beds. As the latter generally builds mountains and high ground it does not offer convenient sites for the placing of boreholes, and further the hard nature of the constituent rocks and the high angle at which they dip would give rise to difficulties in carrying out boring operations.

THE GEOLOGY OF THE AREA AROUND LlCHTENBURG

THE GEOLOGY OF THE AREA AROUND LlCHTENBURG EXPLANATION OF SHEET 54 (LiCHTENBURG) by J. W. von Backstrom, B.Sc., F. W. Schumann, B.Sc., H. D. Ie Roex, M.Sc., L. E. Kent, M.Sc., Ph.D., F.G.S.,.\