PHOTOGRAMMETRIC ENGINEERING
tinctive tone pattern that corresponds to lines
of ground water movement. On the deep
sandy terrace at Goose Bay in Labrador, well-
defined trends in vegetation on the surface
give a precise line of the path of large volumes
of water flowing seventy feet below the sur-
face. This is a micro-feature of the plant cover
caused by an increase in underbrush and
ground cover, rather than by any significant
change in forest type.
Drainage lines often carry valuable infor-
mation in relation to faults, their relative
time of occurrence and their direction of
movement. By a study of an existing stream
channel and related micro-form (abandoned
channels) in the vicinity of a fault, it can be
dated with respect to other structural changes
such as folding.
Hillside seepage is another form of drain-
age not ordinarily considered as large enough
or of sufficient significance to present on
maps. This is a micro-form giving great assist-
ance in defining strata, contacts, and other
structural changes that may otherwise be
buried. It need not be a spring to be visible,
because vegetation will indicate its presence
even if it is only favored by seasonal “weep-
ing." Conditions vary, but these usually ap-
pear as a faint dark line on the hillside, with
several dangling or collecting stringers below
it, representing the spring line and the several
lines of flow that stem from it.
Work by William Fischer of the U. S. Geo-
logical Survey has shown that color photog-
raphy raises the level of visibility of many
micro-features, and in so doing brings them
into the realm of recognition for use in vari-
ous types of analytical studies. An example of
this has been illustrated by comparable pho-
tography in an article by W. W. Baker of San
Antonio, published in the March 17, 1958 Oil]
and Gas Journal. Such a comparison between
black-and-white and color photography of
the same area is especially informative, for it
indicated that although the evidence appears
in both, the color photography tends to em-
phasize certain details that are readily over-
looked in the black-and-white coverage.
For anyone interested in the study of mi-
cro-features a very worthwhile contribution
was presented at the annual meeting of the
American Society of Photogrammetry by
Laurence H. Lattman, The Pennsylvania
State University. 'Technique of Mapping
Geologic Fracture Traces and Lineaments on
Aerial Photographs."*
This discussion of micro-features is in-
tended to present the facts of their existence
and of their importance. It is necessarily lim-
ited since it is not unrelated to many other
factors of recognition; and these factors are
to be used together rather than treated as in-
dependent variables. The subject is also
handicapped here by the obvious and natural
limitations of reproduction that would neces-
sarily be overtaxed by problems equal to that
of enlarging and reproducing the Lord's
Prayer written on a pinhead.
* PHOTOGRAMMETRIC ENGINEERING, Vol. XXIV,
(4) 568 (Sept. 1958).
CS
