106 THE MATSAP VOLCANICS 



usually rather coarse, and the grains are well rounded. 

 There is no general difference between these quartzites 

 and those which make up a large part of the middle and 

 the whole of the upper group. Isolated well-rounded 

 pebbles frequently occur in all these quartzites ; they 

 are made of quartz, quartzite, or red jasper ; the latter 

 often contains magnetite. 



The quartzites of the Matsap group are different in 

 appearance from other rocks in the Colony, and boulders 

 of them in the Dwyka can be recognised with certainty. 



The thickness of the Lower Matsap beds in Hay is 

 estimated to be not less than 3,000 feet. 



The Middle Matsap Beds. 



The distinguishing character of these beds is the 

 presence of a considerable thickness of volcanic rocks, 

 lavas, breccias and tuffs. They have only been found 

 east of the Langebergen between the farms Pauw Fon- 

 tein in the south and Dalgetty in the north, a distance 

 of sixty miles, while the length of the ranges from Ezel 

 Kand to the north end of the Korannaberg is 140 miles. 

 The volcanic rocks may exist over a very much wider 

 area, for as the country is heavily covered with sand the 

 rocks are usually only seen where there are hills. 



At the base of the group near Olifant's Hoek there is 

 a conglomerate with a dark green matrix like that of the 

 overlying volcanic breccias. The lavas are much altered ; 

 they are often arnygdaloidal and seem to have been of 

 the hornblende-andesite type ; original green hornblende 

 and plagioclase are seen in some of the rocks under the 

 microscope, but the greater part consists of green second- 



