156 ILLINOIS STATE ACADEMY OF SCIENCE 



come what they are or whether the soils caused the repre- 

 sentative vegetative assemblages, is outside the province 

 of this paper. 



The alternation of loam and clay found in Ogle County 

 is a thing common to glacial regions. Some limestone resi- 

 dual soil occurs and there are residual sandy areas arising 

 from the disintegration of sandstone. The most marked 

 contrast and the most notable soil difference for vegetation, 

 whatever may be the part the vegetative assemblages play 

 in this, is that between the rich brown or black loam of the 

 gently rolling prairie back from the Rock River and its 

 tributaries and the more rapidly eroding clays, much poorer 

 in humus, nearer the streams. 



NATIVE VEGETATION IN THE PAST 



In the geological past, since the last retreat of the Pleisto- 

 cene ice, it seems certain that there was a time when the 

 vegetation of the county comprised in large part white pine 

 (Pinus strobus) as its chief tree growth. As the climatic 

 change following the retreat of the ice took place through 

 thousands of years, coniferous species became more and 

 more replaced by the tree species that occur as the chief 

 ones today, in response to the conditions furnished by the 

 present climatic cycle. White pine is able to persist still, 

 however, as a relic of the former vegetation. Careful 

 searching of the old records as contained in the county his- 

 tories of northern Illinois and of Wisconsin, and of old maps 

 as well, indicates that for the geologically brief instant dur- 

 ing which white men have been in the region this white pine 

 has existed only in the form of isolated areas and not as ex- 

 tended arms of growth from the north which have since 

 become cut off into these scattered parcels. This evidence, 

 though not conclusive, greatly increases the probability. 

 Since the first coming of the whites about the middle of the 

 nineteenth century even these stands have been mostly 

 wiped out or persist only in the form of a few trees. 



Previous to about 1840 the inhabitants of Ogle County 

 were chiefly Indians. A few French occasionally came to the 

 region that is now the county after La Salle came to Illinois 

 late in the seventeenth century. It has been estimated that 



