THE OLDEST BIOGENIC DEPOSITS 



81 



Fig. 19. Thin section of biogenic pre-Cambrian limestone deposit, dolo- 

 mite series, near Bulawayo, Southern Rhodesia (slightly reduced) 

 (from MacGregor, 1940). 



Fig. 18. Polished and etched surface of biogenic deposits in pre- 

 Cambrian limestone. Dolomite series, near Bulawayo, Southern Rho- 

 desia (x ^/4). Fine lamellar structure in so-called 'dentate band' in- 

 dicates biogenic deposition rather than inorganic recrystalhzation of 

 limestone (from MacGregor, 1940). Scale shows inches. 



