q6 The AmClican (icologist. February, \m:< 
Itasca moraine, the Alesabi • moraine on its southern side 
merges into the flat drift. Its northern hmit is well defined by 
irregular hills rising abruptly over two hundred feet above 
the average surface of the country. The northern edge of this 
moraine marks the dividing line in northeastern Minnesota 
between the heavily covered drift area to the south and that 
part where the drift is very scarce. 
The \'ermilion moraine which lies in the latter area was. 
estimated by Mr. Upham* to have an average thickness of 
twenty-two feet in its greatest development. Northwest of 
the township of Marks this moraine is over a mile wide and 
200 feet deep and possesses the same structure described in 
the other moraines. 
Between the moraines the drift presents an even surface, 
occurring usually in low, rolling ridges, increasing in eleva- 
tion as they approach the front of the moraines. These depos- 
its consist partly of till and partly of modified drift. 
THE NON-MORAINIC TILL. 
Under this term is included the unstratified glacial drift 
which is found in the greater part of northeastern Minnesota 
and usually of no considerable thickness. On account of the 
heavily wooded condition of the region it is difficult in many 
cases to distinguish it from the modified drift. South of the 
Highland moraine the till is not more than twenty feet thick 
and usually only a few feet. In the greater part of this area 
it is covered by the lacustrine deposits of lake Duluth. In 
the triangle between the Highland and Itasca moraines the 
till appears in low rolling ridges with a general slope toward 
the west forming the valleys of the Saint Louis river and its 
eastern tributaries. A large part of this area is covered with 
the usual swamps and muskegs, so that over areas several 
townships in extent the surface varies only a few feet in alti- 
tude. The till in this area consists of alternating layers of 
material derived from the east and the northeast. This was 
described and illustrated by Upham.t' It is also evident that 
in the region immediately north of the Highland moraine the 
upper till layer is of eastern origin, and that in the region im- 
*Op. cit. p. 52. 
t Op. cit. pp. 43 and 44. and Plate IL 
