684 ERNEST H. L. SCHWARZ 



of the bowlders were rough and water- worn. ^ The inabihty of the 

 mind to imagine natural causes for the production of thse facets, other 

 than that which assumes that the foot of a glacier held the bowlders 

 firmly against the floor as the ice moved onward, and ever and again 

 allowed the bowlder to slip and turn slightly, has been sufficient to 

 convert most skeptics to belief in the glacial origin of the Dwyka 

 Conglomerate, and for ten years Mr. Rogers and myself have been 

 slowly converting to this view the travelers who enter the country at 

 Cape Town, culminating in the visit of the British Association last 

 year. 



The Dwyka Conglomerate, and its equivalent in Australia and 

 India, is too well known now to require description here, but I have 

 introduced the account of the part which Mr. Rogers and myself 

 played in the elucidation of the problem in order to show the cre- 

 dentials with which we offer evidence of two more glacial periods in 

 South Africa. The evidence of each was discovered by Mr. Rogers ; 

 the evidence of one, probably Devonian in age, I have examined in 

 the field f the other is probably Archean, and although I have not seen 

 the glacial beds in place, the specimens which Mr. Rogers has sent 

 me afford ample material for confirming his interpretation. ^ 



The rocks of South Africa may be divided into a Pal-Afric and 

 Neo-Afric series, the latter beginning about the close of the Silurian 

 or commencement of the Devonian period, and lasting up to the 

 time of the Kimberley and Stormberg volcanoes, say, to the Jurassic 

 period. The Pal-Afric rocks are pre-Devonian. The resemblance, 

 of some of them to the Lake Superior Archean rocks has suggested 

 a like age for them.^ The enormous displacements they have been 



' Annual Report of the Geological Commission, 1896 (Cape Town, 1897), p. 28; 

 ibid., 1897 (Cape Town, 1898), p. 41; ibid., 1899 (Cape Town, 1900), p. 13. 



2 A. W. Rogers and E. H. L. Schwarz, "Report on the Cederbergen and Adjoin- 

 ing Country," Annual Report of the Geological Commission for 1900 (Cape Town, 

 1901), p. 79; A. W. Rogers, "On a Glacial Conglomerate in the Table Mountain 

 Sandstone," Transactions of the South African Philosophical Society, Vol. XI, pp. 236- 

 42 (Cape Town, 1902); ibid.. Vol. XVI, pp. 1-8 (1905). 



3 A. W. Rogers, "The Campbell Rand and Griquatown Series in Hay," Trans- 

 actions of the Geological Society of South Africa, Vol. IX, pp. 1-9 (Johannesburg, 1906). 



4 E. H. L. Schwarz, "The Transvaal Formation in Prieska, " Translations of 

 the Geological Society of South Africa, Vol. VIII, p. 95 and p. Ixiii. (Johannesburg, 

 1905) 



