SUMMARY CONCERNING DWYKA FORMATION 413 



see t, figure 1), and are described by Anderson {a, page 89) ; and on 

 the Umfolosi river, direction not specified (about longitude 31% degrees 

 east; see u, figure 1), also described by Anderson (b, page 60). In 

 the latter report the Dwyka is referred to as the "glacial Ecca conglom- 

 erate," a change of name which seems to me regrettable, in view of the 

 wide use already gained by the term Dwyka. 



Nearly all the reported observations are thus seen to confirm the general 

 southward motion of the Dwyka ice-sheet, and to indicate that it spread 

 southeast, south, and southwest in a radiating fashion from a central area 

 inferably situated farther north, but not yet determined by observation. 

 The moderate relief of the pre-Dwyka surface inferred from the ob- 

 servations here detailed is confirmed by the accounts given by Eogers and 

 Mellor above cited, and also in various geological sections published by 

 mining engineers, as the result of surface observations supplemented by 

 borings in the search for coal beds in the covering strata or for the gold- 

 bearing Banket in the un deriving strata. Anderson's reports indicate a 

 stronger relief for the pre-Dwyka surface near the coast in Natal than 

 appears to prevail in the interior. 



SUMMARY CONCERNING THE DWYKA FORMATION 



In view of all the foregoing it may be concluded that there is at present 

 no evidence whatever that the Dwyka ice had the form of Alpine glaciers. 

 All reported observations indicate that it was a broad and continuous ice- 

 sheet which spread across about 600 miles of country, east and west, and 

 which advanced at least 500 miles poleward from its apparent source. It 

 moved across a region which bore subdued mountains here and there, but 

 which was reduced to moderate relief by previous erosion over large areas. 

 It seems to have invaded a water-covered area along its southern margin in 

 latitude 33% degrees south. In the marginal area at least the ice advanced 

 more than once, and after its final recession a climate ensued so favorable 

 to plant life that a number of coal beds were formed in the Ecca series 

 which overlies the glacial deposits. It is noteworthy that demonstrably 

 marine deposits are nowhere associated, with the Dwyka, not even in 

 Natal and eastern Cape Colony, where the Dwyka tillite repeatedly reaches 

 the shore of the Indian ocean. 



While much has already been learned, much yet remains to be learned 

 regarding this remarkable formation, particularly regarding certain 

 features which are now well known in association with the till sheets of 

 other glaciated areas. In the central parts of such areas stratified gravel 

 deposits of irregular structure and form are commonly found on the un- 

 stratified till or on the glaciated rock surface, but no such gravels are 



