90 



THE FOSSILS 



Fig. 25. Detailed view of two colonies of Conophyton in transverse 

 section. Pharusian, pre-Cambrian of the Hoggar, Sahara (from Gravelle 

 and Lelubre, 1954, Plate XXVIII). 



addition to those described from South Africa by MacGregor. They 

 are found mainly in the central Sahara, in the general district of 

 the Hoggar. They too are no real fossils, but crusts of limestone 

 deposited by lime-secreting organisms. Comparing these with the 

 earliest deposits of limestone from South Africa, we find that there 

 is ever so much more of them. Both in number of localities and in 

 volume of the limestone deposited, they far exceed their South 

 African counterpart. The age of the deposits from the Sahara is not 

 well known, but it probably is much less than that of the MacGregor 

 deposits. 



The remains from the pre-Cambrian of the Sahara are classed as 

 belonging to the Stromatolites, an artificial taxonomic group com- 

 prising masses of limestone, sometimes globose, sometimes more tu- 

 bular, which do not have a clear microstructure, and which often 



