Fauna and Stratigraphy of the Slormberg Series. 459 



of Somabula. If this white sandstone is Forest Sandstone, then the 

 succession of the beds seems clear. The Escarpment Grits (with a 

 white sandstone carrying Tliinnfeldia below them in the Somabula 

 area) are followed by the Forest Sandstone (seen at Mafungabusi), 

 which is white in its lower part and red above, and this passes up 

 by progressively coarser sandstones of more and more rounded grain 

 through the Transition Sandstone into the Nyamandhlovu Sandstone. 

 Where the Escarpment Grits are absent, as in the district north of 

 Bulawayo, the base of the Forest Sandstone is a conglomerate 

 followed by a Red Marl. If, on the other hand, the sandstone of 

 Mafungabusi represents the top of the Forest Sandstone or the Trans- 

 ition Sandstone, then the Escarpment Grits of the "YVunkie area would 

 seem to equal, in part at least, the Forest Sandstone of the type 

 area. In any case, the correlation with the Stormbergs of the Cape 

 seems clear. Tliinnfeldia is characteristically a Molteno plant, although 

 it occurs sporadically in the Red Beds; and the Dinosaurian remains 

 are closely comparable with those from the top of the Red Beds or 

 the Cave Sandstone. The lithological changes are also comparable 

 with those seen in the Cape. Coarse pebbly sandstones typically give 

 place to finer-grained sandstones with a local intermediate develop- 

 ment of red marls; and the climatic changes are in the same direction 

 as those in the south of the continent, although at any given time 

 conditions seem to have been more arid in the north than in the south. 

 Writing of the Forest Sandstone Molyneux says "The rocks of the 

 group show none of the usual planes of bedding of aqueous deposits, 

 but are thick deposits of sand grains of uniform size without any 

 sorting of coarser material . . . The basal beds are made up of 

 debris resulting from the weathering of granite in situ or which may 

 have been partially sorted into different sizes by storm waters, and 

 in this manner the deeper hollows of the Archaean landscape were 

 levelled up. From this stage onward there is evidence of climate of 

 increasing aridity. The angular shape of the smaller grains in the 

 rock shows that there has, in the lower division especially, been little 

 abrasion or rounding in transport. The deposits are no doubt due to 

 winds that carried dust and particles from a very dry area. To do 

 this atmospheric movements need not have been different from those 

 of to-day . . . The calcrete that occurs in the lowest beds of the 

 Forest Sandstone points to a climate of semi-aridity, but as time went 

 on desert conditions approached and there seems to have been pro- 

 gressive dessication of the whole country. The marls probably re- 

 sulted from the deposition of fine material through the drying up of 

 standing water - - not a lacustrine condition in the manner of lakes 



