376 The American Geologist. December. 1902. 
more of topographic interest than in all the rest of the county. 
On one side of this line is an old, leached, oxidized and deep- 
ly eroded drift overlain by loess ; on the other side the surface 
is occupied by a young, unaltered, uneroded drift upon which 
there is no loess, but large granite bowlders, of types wholly 
absent from the northeastern part of the county, give character 
to long vistas of gently undulating plain. The small north- 
eastern area may be called the Locss-Kansan, the larger area 
to the southwest is the lozvan. 
The Loess-Kansan Area. — Leaving out of consideration for 
the present the valley of the Upper Iowa or Oneota river, the 
Loess-Kansan area presents a series of rounded hills separated 
by ravines which have been cut in the surface of a sheet of 
drift bv flowing water. All the topographic features of the 
region — the hills, ravines and even the deep stream valleys — 
are due to the carving and shaping efifects of ordinary sur- 
face drainage. Outside the river valley, the topography is a 
direct product of the run-off of the ordinary storm waters. 
The underlying drift, as already intimated, is what has been 
called in recent geologic literature the Kansan. The surface 
of this ancient glacial deposit, by reason of long exposure to 
rains and other meteorologic agents, was deeply trenched, and 
the sculpturing resulted in producing, on a small scale, a ma- 
ture type of erosional topography (Fig. i, PI. XXVII). At the 
time of maximum development of the ice sheet which deposit- 
ed the comparatively recent lowan drift, the carved surface of 
the old Kansan till which lay exposed outside the border of 
the lowan ice, was covered with a thin veneer of the fine clay 
called loess.. This loess was moulded over the inequalities 
of the eroded Kansan surface. The deposit was doubt- 
less thicker in some places than in others, but, after all, the 
thickness was practically uniform, the variations being no 
greater than would be found in a mantle of snow laid dowp 
in comparative quiet upon an uneven surface. And thus it 
was that by the deposition of the loess the characteristics of 
the old topography were not veiled or obscured to any note- 
worthy extent. The hills and ravines remained during and 
after the process of loess deposition in the same relative posi- 
tions and with the same relative bights. It is true that some 
minor features of the present topography are due to trenches 
