't^^. 





'^-JKl:u 





Fig. 7^7 Portioti oj thin section of Cryptozoon proliferurn [m2ig\\\'a^<\ X 50). 



(a) Corneous layers, (a') One of these dividing. (Jj) Intermediate stroma with 

 granules of calcite, dolomite and quartz, traversed by canals. 



From a Micro-photograph by I'ROF. PENHALLOW. 



[ To face p. 39. 



