402 IV. M. DAVIS OBSERVATIONS IN SOUTH AFRICA 



small angular specks and scraps of many sorts of rocks, as well as pebbles, 

 cobbles, and boulders up to two or three feet in diameter. We found 

 pieces of granite, amygdaloid, banded jasper, quartzite, quartz, limestone, 

 slate, and several kinds of sandstone. It seemed as if every piece of the 

 finer grained sandstones, especially of a certain fine reddish sandstone, 

 found in the tillite or loose on the surface near the point where it was 

 weathered out, was distinctly and irregularly scratched. It would be im- 

 possible to distinguish these scratched stones from stones of the same 

 texture found in the till of Few England. The larger pieces of sand- 

 stone and quartzite were often grooved, faceted, and regularly striated as 

 well as irregularly scratched, all these markings being characteristically 

 of glacial origin. These surface details are soon lost as the weathered 

 cobbles and boulders creep and wash down the hillsides. The lack of 

 scratches on many of the coarser grained stones is precisely what might 

 be expected in an ancient tillite, if we judge of it by modern glacial forma- 

 tions; for it must not be forgotten that by no means all the stones in 

 Alpine moraines or in Pleistocene till sheets are striated. 



Some of the pebbles in the tillite near Matjesfontein were slightly 

 sheared, some were indented, others wore pointed "beards" of the sheared 

 matrix. Pebbles thus affected, but without surface scratchings, are not 

 uncommon in various nonglacial conglomerates that have been compressed 

 and tilted ; for example, in some of the Carboniferous conglomerates near 

 Boston, Massachusetts, and Newport, Rhode Island. It therefore seems 

 reasonable to refer the shearing and denting of the Dwyka pebbles to the 

 regional deformation which the whole series of formations has suffered 

 in the Karroo, and to regard these as secondary features that have no 

 bearing on the scratches, which are primary features of the formation. 

 None of the outcrops that we here identified as Dwyka by means of their 

 included stone -fragments exhibited distinct stratification, but there 

 seemed to be a heavy bedded structure which determined the development 

 of linear topographic features; in this respect our observations on the 

 following day near Laingsburg are more significant, The normal dark 

 blue color of the unweathered tillite was well shown in several recent cuts 

 along the sides of the post road that we followed; the weathered surface 

 is a dull yellowish gray or brown. This change of color recalls that which 

 takes place when the bluish Pleistocene till of the northern United States 

 is attacked by the weather and rusted to a yellowish gray. The larger 

 forms of this district indicated several folds of moderate intensity, espe- 

 cially in relation to a high synclinal hill a. few miles away, which was 

 identified as consisting of the overlying Ecca sandstones by Mr Rogers 

 from his previous studies here; but the near view of the Dwyka gave us 



