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MICROFORMS AND FEATURES
a low ridge much like a natural levee of a
stream. Within the 'channel" wrinkled flow
patterns can be seen. The degree of preserva-
tion of these features isa comparative matter,
and yet it is elementary to ascribe relative
ages to various flows within an area.
Sandstones and limestones have been con-
sidered by many to have similar if not identi-
cal weathering characteristics in dry areas
and at high altitudes. At high altitudes this
is superficially true but not in the detail rep-
resented by micro-forms. While it is undoubt-
edly possible to find instances where *'it is dif-
ficult to be sure even when on the ground,"
in general weathering along joints and ex-
posed edges of outcrops differs to give a modi-
fied shape to the blocky appearance of jointed
limestone; even dolomites are susceptible to
this form of attack. Related to the same prop-
erties, it is common to find definitive sand ac-
cumulations at the base of gullies below out-
crops of sandstone that do not appear in as-
sociation with limestone. Similarly, calcareous
stains resulting from hillside seepage can be
identified in photographs but are seldom
recognizable on the ground.
In the localization of ore bodies, features of
this order of magnitude are often related to
the presence of mineralization either directly
or indirectly. Iron ores in parts of Canada are
typically associated with thin bedded quartz-
ites while the massive quartzites are sterile.
Casual study permits the mapping of quartz-
ites per se, but only intent study and search-
ing out of details of outcrops will reveal the
essential differences between the two. Thin
bedding develops a lineal trend that is slight-
ly etched by weathering, metamorphic proc-
esses rupture it somewhat, and a slightly
darker tone is discernible in streaks. The com-
bination will be overlooked by all but the
most skilled analyst, and yet it is recorded on
film for all to see.
Faults, fractures, joints, shear zones, brec-
ciated zones, and contact metamorphism all
have important micro-features that generally
offer clues to their presence. Fundamentally
they either offer lines of attack by weather-
ing, or they offer a marked change in the com-
position of the rock, especially where mineral-
ization has occurred. Either effect will pro-
duce a pattern of lines or areas that differ in
drainage or chemical properties, and either of
these will result in vegetative patterns that
bear the imprint of the ground pattern be-
low. Consequently, micro-features of the
plant cover should be given close attention,
especially in the case of forest cover where the
root system may be deep and sensitive to the
presence of mineral salts.
8
This has been borne out by a close study of
plant characteristics in various areas. It is in-
teresting to note that it need not be confined
to mature vegetative cover, although forest
areas recently burned over have had their
value temporarily destroyed. The mature for-
ests of Nova Scotia contain minor areas of in-
tensely distorted trees that are of the same
type as the surrounding forest, but are notice-
able on the ground and in the aerial pictures
by their twisted and otherwise stunted
growth. These areas coincided with actual
sulphide mineralization containing zinc and
copper in a zone of "skarn." Elsewhere the
skarn had no effect on the vegetation except
in other areas that were also mineralized. In
the same manner the presence of nickel in the
soil in South Africa caused the rapid failure of
cultivated crops, and thus led to the discov-
ery of a major ore body where the plants were
being severely poisoned by the metallic salts.
In the first case it was not clearly attribut-
able to an enrichment effect described by
Goldschmidt, but may have been a direct
poisoning of the root system by the ore body
itself, while the second instance was definitely
an example of the accumulation of salts in the
surface by solution of the ore body in ground
water, and an upward migration and precipi-
tation of the salts at the surface over a long
period of time.
Micro-features related to drainage are nu-
merous and serve a wide variety of purposes.
Gravel, for example, can be distinguished
from sand by its vertical drainage system.
Sand absorbs water directly in the sense that
each raindrop soaks in. Gravel, on the other
hand (in terraces, outwash, etc.), concen-
trates water in shallow basins and it then fil-
ters into the ground. The reason for this is
that a gravel mix has a wide spread of miner-
als among its fragments. Some of these weather
to clay and thus produce an overburden of
sandy clay that, compared to sand, is several
degrees less pervious. This weathered mantle
encourages the concentration of water in top-
ographic "Iowa." In the deposition of these
gravels, swift currents left current scars or lo-
calized gouges in the surface that now serve as
infiltration basins. These are easily seen in the
airphoto when the observer's eye and brain
are trained by experience to detect this micro-
feature that can seldom be recognized as such
on the ground. Sands do not possess this fea-
ture because of their comparative resistance
to weathering and the resulting formation of
clays; and because winds blow the sand and
obliterate current scars that may have ex-
isted.
Shallow sands overlaying clay have a dis-
