GENERAL AND INTERIOR DISTRIBUTION CI 



Fishes Tolerant of the Lower Illinoisan Glaciation 



Dogfish Silver chub 



Channel-cat Grass pike 



Yellow bullhead Common top-minnow 



Black bullhead Viviparous top-minnow 



Mud-cat Pirate-perch 



Tadpole cat White crappie 



Brindled stonecat Round sunfish 



Chub-sucker Warmouth 



Striped sucker Green sunfish 



Silvery minnow Long-eared sunfish 



Blunt-nosed minnow Orange-spotted sunfish 



Opsopceodns etnilicB Large-mouthed black bass 



Golden shiner Black-sided darter 



Bullhead minnow Boleosoma camuruni 



Silverfin Sand darter 



Shiner Etheostoma Jessies 



Blackfin Boleichthys fusiformis 

 Ericymba hitccata 



Among the ninety-six Illinois species for which distribution maps 

 have been prepared, thirt3^-four belong clearly to this group of fishes 

 which seem to avoid the conditions common to the flat gray lands of 

 the southern part of the state. Thirty-five species, on the other 

 hand, are distributed over this glaciation in a w^ay to indicate a tol- 

 erance of its conditions if not an indifference to them, the data con- 

 cerning the remaining thirty-three species being ambiguous or inde- 

 cisive in this respect. 



Two facts concerning the soil and waters of the lower Illinoisan 

 glaciation may be held to account, at least in part, for the failure of 

 certain species of fishes to thrive in its streams. Compared with the 

 other regions of the state, this oldest of our glaciation areas has de- 

 veloped its drainage system to a point such that the rainfall runs off 

 rapidly in a large number of small streams, leaving no marshes or 

 ponds to hold back the waters during periods of dry weather. It is a 

 level country whose streams fill up quickly and run down rapidly, the 

 smaller ones drying up completely during the midsummer drought, 

 which is here more marked than farther north. These variable and 

 temporary creeks are, of course, less favorable to the maintenance of 

 a varied and permanent fish population than the waters of the earlier 

 Illinoisan or the Wisconsin areas. 



As a further consequence of its geological antiquity, involving 

 degenerative chemical changes and a long-continued leaching, the 

 soil of this lower glaciation has become an extremely fine-grained, 

 light-colored clay which, when compact, sheds water almost com- 

 pletely, but which washes into the streams as a fine detritus that re- 

 mains persistently in suspension and renders the waters very turbid 

 for a long time after a rain. Standing pools, indeed, never become 



