/'"/■/ ///. Z()o/fi(//c(i/ Sfn<//r.s lit flic Sdiiil Reijloiis of Hit llll 

 iti'is iiitil M/sstsstiijii III fir ]'tillti/s. \W Charles A. PIart. 



(lENERAL Features. 



A.s a ineliiiiinary to the zoological discussion, the general 

 topography of tlie principal sand areas, given in Part 1. of these 

 studies, may lie briefly sunnnarized. These areas occur on the 

 glacial Hood-plain of the broad central basin of the lower Illi- 

 nois valley between Peoria and Meredosia, and of the upper 

 Mississippi tidin ncai' Burlington, Iowa, to Savanna. 111., aggre- 

 gating approximately 2S(I scjuare miles in the Illinois valley 

 alone: and considerable tracts of loose wind-blown surface sand, 

 or "blow-sand" (PI. X.-XV., XIX.). occur in both these areas, 

 which in the Illinois basin are scattered in broad undulating 

 tracts of dune formations, or in ridges running lengthwise of 

 the valley, anti reaching a maximum height of about one hun- 

 dred feet. 



In Part II. Mr. Gleason has(juite fully discussed the present 

 condition of the surface of these areas in the Illinois valley and 

 the effects of wind action in their intimate relation to the plant 

 covering, and a knowledge of these conditions is necessary to an 

 understanding of the sand fauna, which, of course, consi.sts 

 largely of insects and their near relatives. 



The areas of nearly pure sand are the only ones having a dis- 

 tinctly diffei-ent flora and fauna from that of the ordinary Illi- 

 nois prairie. They are most extensively developed upon the 

 western half of the glacial Hood-plain — the half next the present 

 river bottom. Here there is little or no surface drainage, the 

 rainfall being (juickly absoi-l)ed. After a rain the sand soon 

 dries perfectly at the surface, both in winter and summer, thus 

 approximating the conditions of an arid region notwithstand- 

 ing the greater precipitatuin. The striking affinities of its 

 fauna and flora with those of the arid West are evidence of this. 

 Nevertheless, as is more or less the case even in arid lands, the 



195 



