268 F. Prime, Jr.—Lower Silurian Fossils. 
which the latter offers to chemical change of any kind when 
exposed to the action of air and water, and its unaltered condi- 
tion and fresh, bright appearance in rivers and on the seashore. 
But the question as to how the brown hematite got into its 
present condition and whether it was deposited cotemporane- 
ously with the rocks containing it, or subsequently to these, is 
hydromica region of Connecticut. Hence we must have recourse 
to other sources. It seems most doubtful that the mineral, 
ates. Whence was it derived? I have already stated that 
the limestone contains varying proportion of ferrous carbonate 
and of pyrite, and when we consider the enormous erosion 
which the limestone has undergone, the wonder is not that the 
eposits of iron ore should be so great, but rather that they 
should be so small. The ferrous carbonate and the pyrite oxl- 
dised to ferrous sulphate being both soluble in water, the former 
when the wa 
became later decomposed by the action of aerated 
water to hydrated ferric oxide and free silica, which latter we 
where the No. ITI limestones oce 
_ It is well here to emphasize the fact that these brown hema- 
tite ores all belong to the Lower Silurian limestone formation, 
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