Variability of the Earth’s climate - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 98

Figure 2.45. Bubble Rock, Acadia, Maine ( http://flickr.com/photos/iamtonyang/29259194/ ).
action. The direction of the scratches upon these glaciated boulders and pebbles
is also worthy of notice. The scratches upon the loose pebbles are mainly in the
direction of their longest diameter—a result that follows from a mechanical
principle that bodies forced to move through a resisting medium most swing
around so as to proceed in the line of least resistance. Hence the longest diameter
of such moving bodies will tend to come in line with the direction of the motion.''
However, Wright (1920) cautioned:
''A scratched surface is, however, not an infallible proof of the former
presence of a glacier where such a surface is found, or, indeed, of glacial action
at all. A stone scratched by glacial forces may float away upon an iceberg and be
deposited at a great distance from its home. Indeed, icebergs and shore-ice may
produce, in limited degree, the phenomena of striation that we have just
described.''
Wright (1920) went on to say that although longitudinal striations can be
caused by factors other than moving ice, these can by identified by the informed
observer:
''Stones are also striated by other agencies than moving ice. Extensive
avalanches and landslides furnish conditions analogous to those of a glacier,
and might in limited and favorable localities simulate its results. In those larger