Variability of the Earth’s climate - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 101

Finally, Wright (1920) discussed the fact that the southern margin of the
region where unstratified deposits containing striated stones and transported
material was exceedingly irregular in two respects. The southern edge of these
deposits does not follow a straight east-west line, but in places withdraws to the
north (crenate character), and in other places extends lobe-shaped projections far
to the south (serrate character). According to Wright, it was the crenate character
of its southern border that was of most significance. Wright emphasized that the
southern border, with its indentation and projections, was not determined by any
natural barrier based on the geography of the region, but instead was determined
by ''the irregular losses in momentum such as would take place in a semi-fluid
moving in the

line of least resistance from various central points of

accumulation.''
Thomas C. Chamberlain (Geike, 1894) reviewed the geological evidence for
glacial phenomena on the Earth's surface prior to acquisition of ice core and
benthic data on past ice ages. In North America it was found that a tract of
about 4,000,000 square miles had been overspread by glaciers and nearly one half
of North America was covered with drift deposits. He mentioned the concerns of
doubters but concluded: ''the uncompromising evidence of the deposits themselves
and by the ice-grooved rock floor on which these rest, seems to compel acceptance
of the glacial theory.'' Chamberlain concluded that the extent of the ice sheet was
roughly as shown in Figure 2.46 .
These descriptions represent only a fraction of the ample evidence available
to late 19th century geologists that there was a previous ice age, although the
existence of multiple historical ice ages could only be conjectured.

Figure 2.47. Glacial striations (UWESS).