24— THE GLACIAL BEDS LN THE GRIQUA TOWN SERIES. 

 By a. W. Rogers, M.A., F.G.S. 



During the geological survey of the Hay district in 1905 a 

 comparatively small thickness of rock near the top of the Griqua 

 Town series was found to contain numerous boulders and pebbles 

 shaped and scratched in the manner characteristic of stones that have 

 received their linal touches from the grinding action of moving ice. 

 Their discovery gives evidence of the third known, but earliest, period 

 of cold climate in South Africa, the other two being those represented 

 by the glacial deposits in the Table Mountain and the Dwyka series. 



These ancient glacial periods are extremely interesting from 

 several points of view. First, they show that very far back in the 

 earth's history the climate in the areas concerned was such that great 

 accumulations of snow and ice were possible, and that consequently 

 the world's climate of to-day may not be, on the average, hotter or 

 colder than it was then. When the evidence concerns a period 

 possibly older than the oldest known fossiliferous rocks of any 

 country, its bearing on the physical conditions which have prevailed 

 during the evolution of all the known forms of life becomes important. 

 Then, again, the required explanation of the cold climates opens up 

 great questions, which have yet received no probable solution. The 

 fact that a rigorous climate would probably not be local in its occur- 

 rence, that it would not be confined merely to one district in this 

 country, gives us a new means of correlating beds in distant areas. 



At most places where the Griqua Town glacial rocks crop out 

 they are very hard and dark brown or red in colour, owing to the 

 large amount of iron oxides in them. There are several localities 

 where the matrix is dark blue, in colour not unlike that of the Dwyka 

 boulder beds in the south of the colony, but there is much cherty silica 

 in it, which makes it break with a conchoidal fracture. 



The dark blue rock has been found between Kort Kloof and 

 Punt in Hay, on Good Hope in Barkly West, and at Dimoten and 

 Monjana Mabedi, near Khosis, in the Kuruman district. The blue 

 matrix is crowded with grains of quartz, and it also contains many 

 small fragments of dark chert. The included Debbles and boulders 

 are angular, subangular, or rounded, and they range up to two feet 

 in length. Many of them are covered on one or more sides with 

 strise, in the manner characteristic of glacial boulders. Some of the 

 stones are of the " facetted " type, that is, they have one or more 

 nearly flat faces ; in cases where there are two or more faces they may 

 meet along a fairlv well defined edge. These faces are well striated. 



There are other facetted fragments, which were found to be 

 especially abundant at Sunnyside in Hay, though they occur at many 

 other places, but their faces are not striated, or they have very few 

 and .short scratches on them. These fragments are invariably pieces 

 of chert, and their form is probably the result of fracture (along 

 joints before they were enclosed in the matrix. 



Throughout a large part of the rock the pebbles and boulders are 

 distributed without any discernible arrangement, but layers of con- 

 glomerate, two or three feet thick, made up almost entirely of well- 



