THE IRON-FORMATION ON BELCHER ISLANDS 429 
causing variations in the nature of the deposits made during the 
different seasons of the year. 
THE KEEPALLOO IRON-FORMATION 
The term iron-formation is used here as in other writings on 
pre-Cambrian geology for a group of rocks which vary considerably 
in composition, but which together contain conspicuously more 
iron than their associated rocks, and which by natural concentration 
processes are capable of giving rise to iron-ore deposits. 
There is a large body of this formation on the Belcher Islands, 
and the term Keepalloo has been applied as a local name for it, 
since it is so well exposed on the peninsula along Keepalloo Sound. 
It consists of jaspilite, iron carbonate, calcite, probably iron- 
magnesium carbonate, hematite, magnetite, chert, and greenalite. 
A section on Keepalloo Peninsula from the quartzite up to the basalt 
is as follows: 
2 2 OG FEET 
a) A mixture of cherty, sandy, jaspery, calcareous granular rock with 
bandssombprownish=weatnering shale yy eienane 4 Seen ai rs ley Ese 
Dwikeddishvands brownish nissilersialenie: er vias ee le ays ce ne lee tare 17 
GMa ASP ile gna Neem Rn Nees ne MNS Hy aU IRC LRT yas Nd A ME eg 30 
@) aspilite withibands of hematite Orel so: uu se eeiie eis Selec a 39 
ON, VERSE OMIT ESS Sai sei)s EAL I ea a AC EAN 2c Maa 46 
MEN aspcrancdibandsjomleanwhemativterores (ui). 1 ov eyae Wat selec 4): 10 
g) Dull, shaly jasper with bands of bright-red jasper, resembling a felsite 
Ande concalnlMenculbes Om py TILE. oer cuca clea see sigur ete ae see 43 
PAR CoybeN| Ves Ce LN oo at Sar RES CO iS a ee cen RUE MR tS 239 
In many of these rocks small granules may be recognized with 
the naked eye, and they occur mostly in those rocks poorer in iron, 
lying near the top and bottom of the iron-formation. Their greater 
abundance in these rocks is no doubt due to the fact that the iron 
oxides lend themselves less favorably to the preservation’ of such 
structures than silica or carbonates, where there is considerable 
concentration of iron, and also to the fact that when a great deal of 
replacement occurs original structures are likely to be lost. 
A number of thin sections from these rocks were studied, and 
it was found that in nearly all cases the rocks are made up of 
granules of various types. A thin section of the red jasper over- 
lying the quartzite and lying near the base of the iron-formation 
