Pleistocene Rock Gorges. — TTershey. 321 
to the formation of the loess seems evident, else there should 
be a considerable talus on the silt at its base. As the figure 
shows, the bluff on the opposite side of the valley is steep, 
almost precipitous up to a certain bight, above which it is 
inclined at about the same angle as the other side. Appar- 
ently a large part of this gorge is pre-loessial in age. Indi- 
cations of the presence of loess in other gorges have been 
observed. At Martintown, Green county, Wisconsin, the 
Pecatonica river has cut for itself a new course, and the west- 
ern slope of the gorge is almost completely mantled with loess. 
The evidence that has so far been presented for the pre- 
loessial age of a large part of the erosion of the gorges under 
discussion is merely made use of as corroborative of that 
which is now to follow. 
0. Along Yellow creek, in the southern part of Stephenson 
county, there is a series of rock gorges of glacial and post- 
glacial age, scattered along its course for a distance of seven 
miles. A study of these has shown that they are all of about 
the same width, varied slightly, however, according to the 
depth of the gorge. Now one of the series, at the village id' 
Bolton, is so completely buried under loess and other deposits 
of about the same age that for a long time its existence was 
unknown. Its width is about 400 feet, which is the average 
for all the gorges along Yellow creek, although the widtli of 
the old valley is nowhere less than 3,000 feet. 
The lower gorge is situated immediately south of Freeport 
and is peculiar from the fact that the stream no longer flows 
in it, being turned into an old valley to the south of it. But 
that it is of the same age as the rest of the gorges in this 
region is pretty certain for many reasons. It has the same 
width, depth, shape, and relative position as have the others; 
and it is cut at right angles by preglacial tributaries of the 
old valley, showing its much more recent age. The entire 
absence of drift also favors the hypothesis of its Glacial age. 
for had it been in existence before the glaciation of t his region, 
it could not fail to have received a heavy deposit of drift, as 
have all the old valleys in its vicinity. 
This gorge is almost completely buried under loess, and 
there has been no running water in the form of a stream in it 
since this was deposited. Hence its erosion was entirely pre- 
