ORES OF IRON 145 
and are estimated to amount to 5000 million tons of ore with 
from 50 to 55 per cent. of iron, and from -2 to +7 per cent. 
of phosphorus; and the Wabana ores of Bell Island, New- 
foundland, which are also Ordovician, and their five beds, 
varying from § to 20 feet in thickness, along a three-mile 
outcrop, contain, according to A. O. Hayes (G.S. Canada, 
Mem. 78, 1915), between 2000 and 3000 million tons of ore 
with about 53 per cent. of iron and ‘85 per cent. of phosphorus 
and 7000 million tons of lower grade ore. 
These bedded ores have proved one of the puzzles of sedi- 
mentary petrology. The banded ironstones, which consist 
of thin layers of quartz and hematite or magnetite, in the 
pre-Palzozoic rocks of India, Western Australia, and Africa, 
and the Itabirites of Brazil, are probably altered representa- 
tives of this type. 
The bedded ores are generally associated with iron sili- 
cates including glauconite, and also chamosite and thuringite 
which are chloritic hydrosilicates of alumina and iron oxide 
(FeO). Some of the oolitic grains contain a skeleton of silica 
that indicates their formation from silicates, and conversion 
‘nto ore during the formation of the deposit. These bedded 
ironstones have been generally formed under shallow water 
marine conditions. The Clinton and Wabana ores contain 
marine shells and Bryozoa replaced by Hematite, and the 
mud-cracks and ripple-marks show that the deposits were 
Occasionally above water; the deposition may have been 
under lagoon conditions. Three chief explanations have been 
offered of these ores. According to the first, the metaso- 
matic theory (Sorby, Hudleston, and later Hatch and Rastall, 
Petrol. Sed. Rocks, 1913, pp. 210-12), they are limestones 
altered to carbonate of iron, and perhaps later to oxide. 
The second explanation of some of the ore was by saturation 
and partial replacement of sandstone by carbonate of iron 
(Judd). These conclusions rested mainly on the oolitic 
grains and marine shells which were formed as carbonate of 
lime. These explanations are inadequate as many of the 
oolitic grains had been altered into hematite before they had 
reached their present position, and their matrix shows no 
sign of alteration by infiltration. 
The third theory is that the ore was formed by precipita- 
tion on to the sea floor of iron carbonate (which occurs in the 
Ie