THE IRON-FORMATION ON BELCHER ISLANDS 427 
of calcium carbonate by iron oxide in some small concretions in this 
same series of rocks was so suggestive that the attention of Dr. J. 
Ben Hill, of the department of botany, Pennsylvania State College, 
was called to them. Dr. Hill very kindly examined them, prepared 
the accompanying camera lucida sketches (Fig. 14), and the follow- 
ing statement regarding these bodies: 
The specimens in question are generally smaller than the living Cyano- 
phyceae, but are not smaller than the smallest of the living species. In fact, the 
most striking specimens are well above 
the lower range of size in the living 
species. The measurements of the 
objects in the rocks range from o.5 to C20 ae 5 ore 
2.5 microns for the smaller forms to : B oe 
5 and ro microns for the larger. This ~<— oe oe 
is exclusive of the very minute and . S&B & ae 
the very large ones. The shapes of : 
the objects would suggest species in (She, WicCannaeilinstidin Glenines ber 
the two classes (Coccogoneae and J. B. Hill of grains of iron oxide resem- 
Hormogoneae). The isolated spher-  pjing replacements of algal cell struc- 
ical forms resemble some genera of turés. The accompanying scale indicates 
the Coccogoneae as Chrococcus or the diameter of these bodies. 
Gleocopsa, and the specimens showing 
cell-like structures connected to form a filament, some genera of the Hormog- 
oneae as Nostoc or Anoheana. 
Although Dr. Hill and the writer both recognized the great 
difficulty in distinguishing small mineral grains, which often form 
strings and bunches, from organic structures we feel satisfied that 
the sizes, shapes, and arrangement are too regular to be the result 
of simple replacement without some original organic control. A 
further discussion of these smaller concretions will be found in the 
section on the iron-formation. 
The photographs, thin sections, and two specimens of the con- 
cretions were later sent to Dr. M. A. Howe, of the New York 
Botanical Gardens, and to him the writer is indebted for his kind- 
ness in making an examination of these materials. Regarding them 
Dr. Howe makes the following statement: 
This Hudson Bay limestone is of obviously organic origin, and the organ- 
isms contributing to its upbuilding are, it seems to me, in all probability of a 
vegetal and algal rather than animal nature, though the microscopic structure 
