252 PROF. A. H. GEEEN ON THE GEOLOGY AND 



the country, I look upon this as a deposit thrown down from infil- 

 trated water. There were besides a number of transparent, 

 colourless, doubly refracting grains that scratched glass ; most were 

 imperfectly rounded or angular, some few better rounded. They 

 ranged in size from -1 x '1 millim. to -3 X '6 millim., about '3 x '3 

 millim. being an average size. Some contained what looked like 

 liquid-cavities. I have scarcely any doubt that they are clastic 

 grains of quartz. Similar grains were visible in the slice of the 

 Cypher Gat coal already mentioned ; and I found them in the ash 

 of other of the South-African coals. The English coals which I 

 took as standards of comparison contained similar grains, but not 

 in such large numbers as the African coal. In the case of the 

 English coals these grains are probably wind-blown dust, and this 

 they may be also in the African coals ; or, if these were subaqueous, 

 they would be water-borne debris. 



The evidence is far from conclusive, but it is not incompatible 

 with the view that the South-African coals are of subaqueous origin. 



Adopting this view, my notion of the way in which these coals 

 were formed is somewhat as follows. The great lake in which the 

 Molteno Beds were laid down became largely filled up. A swampy 

 surface was formed, dotted over with pools and small lakes of various 

 sizes and depths. In these basins, or in some of them, alternating 

 layers of vegetable matter and mud were laid down. 



A further point of interest is that the coals in some cases seem to 

 have sufiered from contemporaneous denudation before the beds next 

 above them were deposited. In my Report (pp. 11, 12, 13) I have 

 given details of one such instance. When we look at the coarseness 

 of the grits and conglomerates that so frequently lie almost imme- 

 diately above the coal, this is only what might be expected. The 

 wonder is that any coal at all survived under the conditions that 

 must have prevailed shortly after its formation. It is common to 

 find at a very short distance above the coals a coarse grit containing 

 pebbles and well-rounded boulders of quartzite, the latter often 

 larger than a man's head, and in some cases as much as two feet 

 long ; usually there is between the bed and the coal some small 

 thickness of shale, but at Molteno it rested in places directly on 

 the seam. Wherever they came from, these boulders must have 

 travelled a considerable distance ; and it is scarcely believable that 

 there were currents in the lake strong enough to move them, except 

 in the neighbourhood of the mouths of rivers. They may have 

 floated entangled in the roots of trees, but even on this supposition 

 it is hard to see why they are so numerous and widely distributed. 



One most important practical conclusion follows from a review of 

 our present knowledge of these South-African coals. Sanguine 

 speculators, on the strength of having seen outcrops of coal at a few 

 widely separated spots, have assumed that at least one unbroken 

 sheet of coal spreads beneath the large area covered by the Molteno 

 Beds, and have framed most encouraging estimates of the coal- 

 resources of South Africa. It will be most gratifying if these 

 calculations turn out to be correct, but it must be confessed that all 



