File:The Quarterly journal of the Geological Society of London (13365530803).jpg

1850.. DAWSON METAMORPHIC ROCKS OF NOVA SCOTIA. 361
the ochrey red ore. The irregularity of its distribution would result
from that of the carbonate of iron, which, where it now occurs in
the vein, is seen to be confusedly mixed with the ankerite. It might
also happen that the heat would act most powerfully along lines of
fissure, and of this there are some evidences in the appearance of the
vein. The comparatively unaltered state of the ankerite is explained
by the fact, that it is less easily decomposed by heat than the pure
carbonate of iron, or even than the spathose iron found at Acadia
Mine. If a small fragment of the mixed white ankerite and spathose
iron from Acadia Mine be exposed to a low red heat with access of air,
the carbonate of iron is completely decomposed, before any other
change than a slight discoloration is produced in the ankerite.
Hand specimens from the Acadia Mine often present appearances
highly illustrative of the relations of the red ore to the other ingre-
dients of the vein, and confirmatory of the above views of its origin.
Fig. 4 is a sketch of one surface of a specimen of this kind.
Fig. 4. — Surface of a Hand-Specimen from Acadia Mine.
a. Ankerite.
b. Spathose iron.
c. Red iron ore.
d. Fragment of slate.
e. Ankerite with surface changed into yellow ochre.
/. Fissure lined with red ore.
The brown hcematite is apparently confined to the superficial parts
of the vein; and indeed appears to have been more abundant in
those parts of it which have been removed by denudation, than in
any now remaining. It is no doubt a product of the action of water
on the carbonate and hydrated oxide of iron, near the outcrop of
the vein.
The sulphate of barytes, occurring in small quantities in some
parts of the vein, must also be a product of aqueous infiltration.