1912] GLEASON—PRAIRIE GROVE 39 
Chicago and Eastern Illinois Railway, not far from the village of 
Royal. There were several other isolated groves in the county, 
most of which have been entirely destroyed by cultivation. Of 
these, Bur Oak Grove is the largest and the most significant 
phytogeographically. The remaining forest areas of the county 
are along the Sangamon and Kaskaskia rivers, and Salt Fork of 
the Vermillion River. The last two rise in the county, and the 
upper five to ten miles of their course is in the prairie. 
The present length of Bur Oak Grove is about three miles from 
northeast to southwest, and its width about one mile. It is certain 
that it was originally somewhat longer, and it probably had a 
greater average width. Its outline is and has always been very 
irregular. In recent years cultivation has broken it up into many 
small detached portions. There is no easily accessible map show- 
ing the location of the grove in detail. The Urbana sheet of the 
Topographic Survey just misses the grove on the west. Just 
southwest of Bur Oak Grove, however, are two or three other 
detached groves of similar topography which appear on the map. 
These areas are indicated in green near Glover station. The 
peculiar topography associated with these groves is scarcely shown, 
even on a map with contour intervals at ten feet. 
The most striking physical feature of the grove is its peculiar 
surface topography. Surrounded on all sides by level prairie 
country, it is sharply and conspicuously distinguished by its 
irregular surface, which consists of alternating elevations and de- 
pressions. The elevations are of about the same height, and the 
intervening depressions are also of a very uniform depth. The 
width of the depressions varies from a hundred feet to a quarter 
of a mile; their length from a few hundred feet to half a mile, or 
perhaps more; and their depth is usually about ten feet. Their 
shape accordingly varies from almost circular to linear, and those 
of the latter shape frequently resemble abandoned channels of some 
water course. They lie in every conceivable position, and may 
branch or anastomose in any way. As a result of the general 
irregularity, the intervening elevated ground may consist of circu- 
lar islands, extended surfaces, or long and narrow, straight, curved, 
or branching ridges. For convenience, they are here always 
