KNOWLEDGE 



[Much 2, 1896. 



Copper ore occurs at various places near the upper 

 waters of the Limpopo as well as in the north-east of the 

 State, and with f^alcna, sulphide of lead, in veins in granite 

 at the Albert Miiio. 



Lead ores are mined in the western part of the State in 

 calcareous rocks near the source of the Groot Marico, and 

 at Ilamerkop, near .lacobsdal, on the Klein Marico. 



Tin ore has been found in alluvial deposits on the 

 Swaziland borders, and there are thin stanniferous veins 

 in the granitic rocks ; but it has not yet been discovered 

 in paying quantities. 



Zinc blende sometimes occurs associated with galena. 



Iron ores, liaMnatite, limonite, magnetite, and iron 

 pyrites, are abundantly distributed in small quantities. 



Mercury ore, cinnabar, occurs east of Barberton : and 

 cobalt and nickel, as cobalt bloom, smaltine, and nickeline, 

 to the north of ?.iiddleberg. 



Of non-metallic minerals, diamonds have been obtained 

 just within the Transvaal, near Bloemhof on the Vaal 

 lliver, and near its confluence with the Makwsi Eiver. 

 Only small stones, however, have been found, ranging from 

 one to five carats. 



Salt occurs in beds to the north of Pretoria, and also still 

 further north beyond Olifant's Eiver, in the Zoutpansberg 

 district. 



Although true limestones appear to be wanting in the 

 Transvaal, there is a calcareous sandstone that on being 

 burnt or calcined yields lime for economic purposes ; and 

 in one locahty there are caves with stalactites, resulting 

 from the dissolving out of the calcareous matter from the 

 rocks above. 



Coal is a most valuable product of any country, but 

 especially so when motive power for machinery is largely 

 wanted, and there is not a continuously abundant water 

 supply in the rivers available for mills". These are the 

 conditions that give to the coal-bearing rocks of the 

 Transvaal great importance. 



The coal-bearing rocks here are in the lower division of 

 the very extensive South African formation called the 

 Karoo formation. To this division the name " Molteno 

 Beds " has been given, but its geological age has not yet 

 been satisfactorily determined, since the formation as a 

 whole, and the coal-bearing rocks, as well as the coal 

 itself, differ considerably from the Carboniferous rocks and 

 the Coal Measures of this and other countries ; and the 

 fossils, although similar, are so few and of such a general 

 character that they do not afford a sure ground for corre- 

 lation. The strata are almost horizontal, and so overlie the 

 older uptilted rocks uncouformably — indicating, therefore, 

 a much later age. They form, as a rule, high ground, and 

 constitute an extensive and continuous area of the High 

 Veldt, and also occur as patches sometimes overlyin" the 

 primative granitic rocks. 



The beds of coal are not continuous, as in the liritish 

 coalfields, but in more or less lenticular masses, usually 

 horizontal, but on slightly difi'erent horizons ; though 

 there are some seams now known to be continuous for 

 miles. The thickness of the seams varies much, from a 

 few inches upwards ; at Belfast there are three beds of a 

 total thickness of thirteen feet. Though the amount of 

 coal in the rocks of the Transvaal is very great, the quality 

 does not appear to be high, some of the samples giving a 

 large percentage of ash; the Belfast coal gave about 

 twenty per cent, of ash, but that of the Douglas Mine only 

 eight per cent. There is also much iron pyrites in the 

 shaly matter in the coal, rendering it a dangerous coal to 

 stack in large quantities. It is generally very inferior to 

 English coal, and unfitted for metallurgical purposes ; but 

 nevertheless it is suificiently good for ordinary furnace 



cial for steam boilers, and this is the principal require- 

 ment of the Transvaal. Near the Vaal River, and near its 

 confluence with the Klip Uiver on the southern boundary, 

 coal is worked, and also at Daggafontein and near the 

 Witwatersrandc at Boksberg, and the Brakpan Colliery, 

 whore the output amounts to thirteen thousand tons a 

 month. 



With the addition of good building stone, furnished by 

 its sandstones, a vast and varied store of valuable economic 

 minerals available for the use of man is within the bounds 

 of the South African Republic. 



THE 



WAVES.-III. 

 FORCE OF SEA WAVES. 



By Vauchan Cornish, M.Sc. 



WlIl'jN wind blows over the surface of the sea the 

 energy of the lower layers of moving air is 

 employed in raising waves and in giving them 

 a forward motion. The mechanism by which 

 energy is thus imparted from wind to water 

 is not very well understood, for only one aspect of the 

 phenomenon can be observed, namely, the formation of 

 the iriiter-vfa.\e3. Of the air-waves which, it is believed, 

 are generated at the same time we know but little. 



In deep-spa waves which have been raised by the wind, 

 but are no longer subjected to its force, the water particle 

 moves uniformly, under constant pressure, in a circle 

 whose horizontal diameter lies in the direction in which 

 the wave travels. In the upper half of the circle the 

 motion is forwards, whilst the backward swing is on the 

 lower level. Thus at each swing one-half of the energy of 

 motion is transmitted forwards. In virtue of the energy 

 so transmitted the waves continue to travel as free waves 

 when no longer propelled by the wind, and thus spread 

 beyond the tract which has been agitated by the storm. 



On the other hand, after each complete swing of the 

 water one-half of the energy of motion is retnincil, so that 

 in the original losus of a storm the sea continues to be 

 agitated long after the wind has lulled ; whence the per- 

 sistent turbulence of the sea. 



If we fix our attention upon a wave-crest of unusual 

 height (far from the shallows of the shore) and watch the 

 crest as it advances, we shall find that after a time it loses 

 its pre-eminence. At first it seems as if the observer had 

 failed in the attempt to fix his attention upon a particular 

 crest ; but repetition of the observation gives the same 

 result. If when the crest has lost its pre-eminence the eye 

 be turned upon the crest which follows next, it will be seen 

 that this in its turn towers above its neighbours. This 

 second large crest will in like manner diminish in size, and 

 will then be followed by a larger crest. Thus the energy 

 of the wave-motion is seen to be transmitted more slowly 

 than the waves themselves advance. As a wave-crest 

 passes over each point in its course it picks up and carries 

 oil half the energy of motion at that point, but the other 

 half lags behind. For this reason it is impossible when 

 water has the circular swing for a solitary icair to exist ; 

 there must always be a ijniup of iiarc.s. 



This may be illustrated by throwing a stone into a pond, 

 a simple experiment from which much may be learnt. 

 The mere displacement of water by a falling stone gives 

 rise to a numerous group of waves, which continue to travel 

 over the surface of the pjud long after the water at the 

 original point of disturbance has become quiescent. 



On a freely undulating sea the water in its circular 

 swing do3S not strike a floating body. The great rounded 

 crest of an ocean wave, towering above the ship's bow, looks 



