a 
J. D. Dana—Drifiless Interior of North America. 255 
the Wisconsin driftless area appears to be a consequence, as 
Professor Irving urges, of the great depth of the Lake Superior 
trough—over a thousand feet below the present surface of the 
water—and its lying in a southwest-by-west (or about 8. 55° W. 
direction, which was nearly that of the glacier motion in that 
part of North America. For this would have determined the 
nesota and Iowa to Missouri, a distance of five hundred miles, 
this being shown by the bowlders of copper. Whatever the 
pitch along that course, it was twice as great toward the Wis- 
consin driftless area, since the northern border of the area is 
hardly half as far. Down Lake Michigan the pitch continued 
into Illinois and Indiana; but the Kettle Range west of Lake 
Michigan, running along the east front of the driftless area, 
marks out, as Professors Chamberlain and Irving show, its 
moraine termination in that direction. d 
The eastern parallel branch of the Kettle Range lying 
between the Green Bay Valley and Lake Michigan, which, 
according to these geologists, is also a moraine ridge, is evi- 
dence, as they observe, that at the time when it was formed, 
the glacier of Green Bay Valley was distinct from that of 
ke Michigan. It seems probable that when the Glacial era 
was at its height, the two were merged in one glacier; but that 
later, as the ice diminished, the former became independent, 
and that then the eastern Kettle Range was made. 
3. The earth's axis had the same position in the Glacial era as 
now, if the driftless character of the Wisconsin area depended on 
the climatal conditions explained. The concordance between 
the limits of the drier areas of the Glacial era and those of the 
present time, and especially the fact in this respect with regard 
to the isolated area in Wisconsin sustains this proposition. 
The probability that such was the trath was long since made 
Apparent by the observation that the southern termination of 
e glacier in North America and Europe was very nearly 
along what is now the course of the same identical oe 
The position and extent of the Wisconsin driftless area affo: 
more precise and positive evidence. 
