THE IRON-FORMATION ON BELCHER ISLANDS 425 
carbon is left on dissolving the rock in cold or hot acid. No 
definite cell structure can be recognized in this carbon, but in 
Fic. 12.—The smaller type of algal concretions in the limestone on Tookcarak 
Island. 
some of the granules in the calcareous beds of the iron-formation, 
a little higher up in the series, grains of iron oxide, now replac- 
ing the calcareous matter, show such a distribution, size, and 
