204 



Grout and BrodericJc — The Huronian. 



concentrically, so that it is clear that the precipitation 

 and deposition of fragments were about simultaneous. 

 Leith notes 6 that under the microscope the shapes of 

 granules can be seen to have been retained by the chert 



Fig. 4. 



and iron oxide. This no doubt refers to greenalite gran- 

 ules which are altered to chert and iron oxide. Quite 

 aside from this alteration effect, however, there is clear 

 indication of precipitation of chert in concentric layers 

 around some fragmental granules. 



Microscopic examination revealed no cell structures in 

 the cherts. Recrystallization of the cherts has probably 



6 Loc. cit. 



