262 Report S.A.A. Advancement of Science. 



rounded pebbles, occur immediately below the unbedded rock at 

 several localities, and thin, lenticular layers of gravelly rock were 

 noticed in the unbedded boulder rock at Punt and Good Hope. 

 Below the glacial horizon there is generally found a coarse iron- 

 stained grit, several feet thick. 



The boulders and pebbles are chiefly made of dark chert. Some 

 of them are nodular lumps, usually discoidal or elliptical in shape, 

 with a distinct banding parallel to the plane in which the two longer 

 axes of the nodule lie. These nodules are often covered on their 

 flatter sides with the glacial scratches. Quartzite and grit pebbles are 

 not infrequently seen, and fragments of a white-banded marble, very 

 fine grained, occur in the blue rock at Punt, Good Hope, and Monjana 

 Mabedi. In the red and brown outcrops these limestone fragments 

 are represented by cavities in the matrix partly filled with iron oxides ; 

 in the red rock the iron oxide is in the form of specular iron lining 

 the cavity and filling it to a greater or less extent. 



So far as my observations have gone, fragments of granite and 

 other igneous rocks are not present in these beds, a striking point of 

 difference from the other glacial boulder beds in the Colony. 



The red and brown rocks certainly owe their colours to changes 

 which have taken place subsequently to their deposition. In some 

 of these rocks there has been an addition of iron compounds, but it is 

 not yet known whether this access of iron is in all cases a surface 

 phenomenon, i.e., that the iron has collected near the surface from 

 the immediately underlying rock, or whether it has been brought 

 from a distance. The fact that the more ferruginous and heavier 

 varieties are particularly noticeable where the lower beds are 

 hasmatitic jaspers, as along the west side of the Ongeluk-Witwater 

 syncline, and the fact that the blue matrix has only been found where 

 the lower beds are blue or brown, although there is no such change in 

 the surface conditions as would account for the difference, make it 

 probable that generally the increase in iron has not taken place at the 

 present surface. In this connection it should be remarked that the 

 processes by which the bulk of the Griqua Town beds became con- 

 verted into ferruginous jaspers were completed at the time of the 

 formation of the Dwvka boulder beds, for large pieces of rock, which 

 very probablv came from the Griqua Town beds, have been found in 

 the Dwyka, and in Prieska and Hay the normal Dwyka still rests 

 upon the ferruginous jaspers. 



At two places, in a skiit on the west side of the Paling ridge, 

 and near a dried-up fountain at Monjana Mabedi, the boulder beds 

 have been found to be more thoroughly weathered than elsewhere, 

 and thev then have a most remarkable general resemblance to both 

 the weathered glacial beds in the Table Mountain series in Pakhuis 

 Pass, Clanwilliam, and to the Dwvka in its weathered state. The 

 onlv obvious difference in the exposures is due to the absence of 

 other than chert, quartzite and grit boulders in the Griqua Town 

 boulder beds. 



The glacial horizon has now been found to extend from near the 

 Orange River in Hay to about 20 miles south of Kuruman, a distance 



