THE IRON-FORMATION ON BELCHER ISLANDS 423 
Low had observed the concretionary structures mentioned 
above, and he states regarding the rocks associated with them: 
‘“‘No fossils have as yet been discovered in any of the beds of this 
formation, but the presence of certain concretionary forms in its 
limestones and the amount of carbon in many of the shales lead to 
the belief that at least low forms of life existed at the time these 
rocks were deposited.’* Leith also mentions them, in the Rich- 
mond Gulf region, as follows: ‘The limestone floor has great con- 
cretionary structures up to two feet in diameter, the sides of the 
concretions locally open on one side and locally opening out into 
waved and crenulated bedding lines, interpretation of which the 
writer does not attempt, but which probably tell of conditions which 
if known would indicate the depth of water and other significant 
conditions of the r formation.’” 
On the Belcher Islands these bodies form whole reefs in the more 
or less silicified limestone of the Belcher series, making up a thick- 
ness of over 400 feet (Figs. 9, 10, 11, 12). There appear to be two 
types, one smaller than the other, but as to whether these should 
be classed as distinct forms or simply regarded as concretions in 
different stages of maturity is not yet settled. The fact that the 
smaller ones form a large, reeflike mass near the top of the algal 
limestone and near the line where the rocks change in character 
suggests that they are incompletely developed specimens of the 
larger type. Both types are spherical to subspherical bodies con- 
sisting of concentric layers, and they vary in size from an inch to 
over fifteen inches in diameter. The larger type is seldom less than 
four inches, and the smaller seldom more than four inches, in diam- 
eter. The larger ones are more regular in form, being much more 
nearly spherical than the smaller ones, and they also show the con- 
centric lines of growth more distinctly than the smaller ones, which 
show a tendency to be rather disk-shaped. The distinctly crenu- 
lated character of Cryptozoon proliferum is not found in many of 
these specimens. They are probably more like Cryptozoon steeli. 
The concretions consist chiefly of calcium carbonate and can 
be almost entirely dissolved in cold hydrochloric acid. There is, 
1A. P. Low, Geol. Sur. of Canada Ann. Rept., XIII, Part D, p. 46D. 
2C. K. Leith, op. cit., p. 240. 
