96 GLACIAL BOULDER-BEDS 



in thickness but have been found throughout the area 

 occupied by the Lower Griqua Town beds. 



Wherever the top of the Lower Griqua Town beds 

 is exposed a peculiar boulder rock has been found lying 

 within some thirty feet or less of the overlying Ongeluk 

 lavas. It resembles a glacial till in having boulders 

 and pebbles scattered through it at random, without 

 any sort of arrangement according to size ; the matrix 

 is, where least altered, a fine-grained calcareous and 

 siliceous rock with occasional grains large enough to 

 be easily visible to the naked eye. The boulders and 

 pebbles are often found to have one or more sides 

 flattened and covered with scratches in the manner 

 characteristic of stones found in tills. They are made 

 of crystalline limestones and chert, and occasionally 

 quartzites and grits, but such rocks as granites, schists 

 and diabase have not been found as pebbles, though 

 chips of felspar and flakes of mica, probably from granite, 

 have been seen in thin sections of the matrix. 



The general character of the rock and the shape of 

 the striated boulders are extremely difficult to explain 

 without assuming their glacial origin, even though a 

 locality where the rock rests unconformably upon a 

 striated surface has not been found. It is, in fact, a 

 tillite, resembling in its chief features the tillites in the 

 Table Mountain series and the Dwyka, the latter of 

 which has been recognised by several geologists who 

 have had wide experience of recent and Pleistocene tills 

 to have been formed under the same kind of circum- 

 stances as these. 



The source of the pebbles and boulders is not known ; 



