432 E. S. MOORE 
similar to those described in the last section, ovoid, ham-shaped, 
irregular, and rarely spherical. In size they vary from o.14 to 
o.gt millimeter in diameter. They are colorless, reddish brown 
to deep brown, and apple green. ‘The colorless ones consist of very 
finely granular silica with a matrix of chert and chalcedony. A 
great deal of calcite is distributed through the section, and one small 
granule consists entirely of calcite, thus suggesting that all the 
granules may have been calcite originally. 
The green granules vary from apple green through brownish 
green to dark brown, depending upon the amount of iron oxide 
which has developed by alteration. They show very little double 
refraction and no pleochroism except in some places where they are 
altered to little rosettes of extremely small radiating needles of 
what is apparently an amphibole, with higher bi-refringence than 
the chlorites, but lower than actinolite or griinerite. Some granules 
are largely altered to magnetite, and in others rhombs of limonite. 
indicate the change of siderite to limonite. In many of them the 
same cell-like arrangement of the quartz grains mentioned in the 
last section may be seen. : 
It seems evident that these green granules consist of iron silicate, 
and of the silicates, thuringite, chamosite, and greenalite commonly 
found in iron-ore deposits, the characters correspond most nearly 
to Van Hise and Leith’s description of the greenalite granules of 
the Mesabi Range." 
ORIGIN OF THE IRON-FORMATION 
From the descriptions given above it is evident that we have 
on the Belcher Islands an unusual development of large concre- 
tions whose origin can only be attributed to organic processes. 
We have further hundreds of feet of rocks consisting chiefly of 
minute granules, some of which at least show good evidence of 
being of organic origin from the widespread occurrence of apparent 
traces of plant remains in them. If these granules be compared 
with certain siliceous granules in the Upper Cambrian limestones 
of central Pennsylvania, which grade into typical odlites, it will 
‘Van Hise and Leith, ‘“‘Geology of the Lake Superior Region,” U.S. Geol. Sur. 
Mon., LIL (1911), 165. 
