503 
In these areas there is still considerable pasture or fallow land. 
There is even an occasional remnant of a rail fence, while thickets 
in the fence corners, brush along the fences, and other forms of 
agricultural untidiness are a protection to wild animal life in general. 
Outside these river valleys there were a few scattered groves, 
from 20 to 160 acres in extent, which served as landmarks and were 
known by special names for many miles around. With the excep- 
tion of the moraines and the narrow belts along the larger streams 
the country was naturally a very gently rolling prairie. It bore, 
too, the character of a country of recent geological age where drain- 
age was still undeveloped. The windrows of glacial drift were very 
imperfectly cut through, and shut in the surface water in shallow 
basins. The encroaching vegetation and vegetable deposits had 
changed these basins to what were shallow sloughs or marshy lakes 
in a rainy season, but became soggy meadows in time of drought. 
Though the main streams had cut deep into the till, the smaller head- 
waters had eroded but little. Indeed, along their upper courses 
their erosive action must have been zero, and they represented little 
more than the course along which the drainage waters seeped their 
way, through dense vegetation and matted debris, to a lower level. 
For detailed study of the distribution of its mammals, the 
county may be divided into 
Till plains, Groves, 
Moraine ridges, Permanent pastures, 
Wooded bluffs and ravines, Flood-plains. 
TILL PLAINS. 
(Plate XXVI., Fig. 1.) 
Under this designation are included the extensive, nearly level 
prairie areas lying between the higher, more uneven moraine belts. 
These plains are the most characteristic and the most extensive 
feature of the topography of the county. They vary little in level, 
often less than five feet within a square mile. Portions were origi- 
nally wet and swampy, but all are now drained and under thorough 
cultivation. Some of these areas, however, although extensively 
underdrained and capable of thorough cultivation in ordinary 
years, are nevertheless sometimes covered by a few inches of water 
during the early spring, and such areas—usually of small extent— 
(2) 
