146

small accretions of hematite. Narrow, gash-like veins of quartz are also
present. This is the only body of ore seen. It clearly terminates to the
east, but to the northwest all exposures cease and it may be, though it
seems unlikely, that the body continues in that direction down the steep slope.

In the artificial exposures at localities D and KE, on the southwest
slope of the ridge, the same general phenomena are visible as in the vicinity
of the dyke, but nowhere is any ore-body visible. In some places, 25 per
cent or more of the volume of particular layers of limestone a few inches
thick consists of the irregularly ovoid hematite accretions and in some
instances the bodies are so numerous as to constitute almost solid layers
of hematite several inches thick.

MODE OF ORIGIN

Former describers of the hematite occurrences on Fenwick mountain
have referred to them as being of the nature of veins, impregnations, or
replacements. They have also been referred to as examples of bedded
deposits, originally composed of limonite since changed to hematite.

The ore occurs in short veins cutting the igneous rock and the sedi-
ments; it occurs in seams along what appear to be planes of fractures
traversing dense, siliceous strata and quartz veins; and it also occurs
impregnating and replacing sedimentary strata. In addition, a less
pure form of hematite occurs in small bodies in the sediments. These
small bodies may also be impregnations or replacements, but perhaps are
ferruginous accretions which grew while the enclosing sediments were
being formed.

The purer hematite that occurs in veins cutting the igneous rock and
in seams along fracture planes in quartz veins cutting the igneous rock,
must have formed after the intrusion of the igneous body. The one
comparatively large mass of ore on the ridge top at the southeast edge of
the dyke and the hematite seams in the shattered, dense, siliceous rocks
presumably formed at the same time as did the veins in the igneous rock
and the seams in the fractured quartz veins. The hematite that impregnates
and partly replaces the sediments along the edges of the dyke
resembles, in general character, the hematite of the veins and seams and
the impression was received that all this hematite had formed at essentially
the same time after the intrusion of the dyke. But all these modes of
occurrence on the northeast slope seem definitely connected with the
edges of the dyke. The veins, seams, impregnations, and replacements
occur only along these edges and in the case of the layers showing replace-
ment, the hematite decreases in amount outwards from the dyke.

The small, accretion-like bodies of impure hematite may belong to an
earlier generation than the veins, seams, and replacement masses of purer
hematite. Within the body of hematite on the ridge top at locality A are
small masses of unreplaced rock, some of which carry the accretions and
give the impression that the accretions were in existence prior to the com-
mencement of the process of replacement. The accretions as developed
on the southwest slopes characterize a particular horizon in the sedi-
ments, 50 feet or more thick, and this is the horizon of the strata on the
ridge summit at locality A where the same type of bodies also occurs. If it
were certain that these accretions were confined to this particular horizon
in the strata then it would be reasonably established that the accretions
were original constituents of the sediments. Unfortunately the requisite