40 BOTANICAL GAZETTE [JANUARY 
referred to as ridges, irrespective of their shape, while the depres- 
sions are called sloughs, after the general usage of the region. 
The slope from ridge to slough is always gentle, never exceeding and 
seldom reaching 10°. No attempt will be made to explain the origin 
of this peculiar topography, except to suggest that it may be in 
some way connected with or caused by the glacier which deposited 
the conspicuous moraine a few miles farther north. 
These sloughs received all the surface drainage from the ridges, 
and were originally filled through most of the year with standing 
water. During the spring rains they overflowed at the lowest 
point in their margins into neighboring sloughs, and in this way 
the whole area was converted into a network of ponds. During 
the summer the water was lost by underground drainage and evapo- 
ration, until by October some of the sloughs were entirely dry. 
These conditions have greatly restricted agriculture, and it is to 
them that the grove owes its preservation. With the increasing 
value of land, tile has been laid, ditches dug, and most of the 
sloughs reclaimed. In them the soil is black and deep and is gen- 
erally planted to corn. Others are left in pasture, although they 
support a better growth of weeds than of grass. A few are so deep 
that they cannot be profitably drained, and are still occupied by 
permanent ponds. Probably half a dozen of these ponds are left, 
and they now constitute the only natural bodies of permanent 
standing water in the county. Although the soil on the ridges 
is not so black or so deep as on the surrounding prairies, a part of 
the forest which covered them has been cleared, and the staple 
crops are grown. The rest of the forest is used for permanent 
pasture. 
The forest cover of the ridges shows a considerable variation in 
specific composition from south to north. Near the south end the 
forest is open, the trees are comparatively small, and there is scarcely 
any deposit of leaf mold (fig 1). The prevailing trees are Quercus 
imbricaria, Q. velutina, Carya ovata, C. cordiformis, with occasional 
trees of Juglans nigra. The actual proportion of these species varies 
widely. Quercus imbricaria is usually most abundant, but there are 
some small areas in which Carya ovata is dominant. The trees now 
seldom exceed a foot in diameter, but the present forest is almost 
