430 THE DEVONIAN SEA 



had been deposited. The presence of plant remains in 

 the Bokkeveld beds, along with the marine shells, shows 

 that the land on which the plants grew was not far off. 

 In the account of the Bokkeveld beds in chapter iv., 

 the generally noticed increase of sandstone towards the 

 north and west was explained on the supposition that 

 the sediments were chiefly derived from land lying north 

 and west of the districts where the Bokkeveld beds 

 occur. 



Marine conditions prevailed in the southern part of 

 Africa till the middle of the Bokkeveld period, when 

 open connection with the sea seems to have been cut 

 off, for in the muds, shales and sandstones of the Upper 

 Bokkeveld and the Witteberg series only plant remains 

 have been found. The cause and manner of this loss 

 of connection with the ocean cannot be explained, as 

 the evidence which might solve the problem lies below 

 the waters of the Atlantic. The abundance of sandstones 

 in the Witteberg beds, with their occasional white quartz 

 pebbles, often in some respects closely resembling the 

 Table Mountain sandstone, point to a recurrence of the 

 conditions under which the latter was formed, though 

 the frequence of thick shale bands proves that much 

 of the finer grained sediment came to rest within the 

 Colonial area in Witteberg times, while in the earlier 

 period of the Table Mountain sandstone much less of 

 the clays and silt, which must have been produced 

 during the destruction of the rocks that furnished all 

 the sand now forming the Table Mountain sandstone, 

 remained in the same area. 



Plants are the only fossils hitherto discovered in the 



