248 



Surface features. — The northern region of Indiana is entirely within the regior» 

 of ancient giaciation ; its surface is characteristic of the drift areas. It is char- 

 acterized by streams which are almost entirely in glacial debris, sand, gravel, 

 boulders and clay variously contributing to the bottom features of the several 

 streams; in the low-lying and imperfectly drained prairie regions are many lakes 

 of varying areas, as the seasons are wet or dry, and of very great differences in 

 their comparative sizes. These lakes are, for the most part, shallow, with more 

 or less sandy, or gravelly, or bouldery, bottoms and shores. An abundant marshy 

 vegelatioQ surrounds them, and sluggishly flowing streams serve to drain most of 

 them. The whole region being so heavily covered with glacial deposits there are 

 few elevations and they are mostly portions of the several terminal moraines; 

 the country rock rarely, if ever, appears in either natural or artificial sections. 

 The beds of all the streams are full of glacial boulders and sands or gravels. 



The Kankakee basin differs in no essential respects from those just described. 

 It is worthy of note, however, that the course of this river, as indeed that of all 

 within the drift area, has been largely determined by the moraines which cross 

 the State in a series of irregular lines, most of which are north of the Wabash. 

 The same general truth is apparent of the Maumee Eiver, the course of which 

 has certainly been determined by the glacial detritus over which it flows. But 

 the general drainage level is so slight that there are sections, as those between 

 Huntington and Fort Wayne, where, at seasons of the year when the streams are 

 all at full flood, the waters indifferently flow to either the Atlantic or the Ohio 

 drainage. This important fact will be again noted in the matter of distribution 

 of the mollusks of the two regions. 



The region drained by the Wabash and the White rivers is, in many respects, 

 widely different from the region previously described. For many miles of its 

 course the upper Wabash flows through canons cut into the country rock within 

 its own life history ; at Wabash and Peru the real nature of this corrasive work is 

 well exhibited. But higher up the canon is deeper and the stream less wide; 

 suddenly it rises high on the siirface and flows along over glacial detritus, like the 

 rivers farther to the north. That it flows, for some part of its course, in pregla- 

 cial channels is true, but it is also true that it has abandoned those channels in 

 other portions of its course. It results from this that its character changes at va- 

 rious points along its course ; a fact of importance that should be borne in mind 

 in discussing the distribution of the fresh-water mollusks found in its waters. 



Both the basins of the W^hite rivers present two features in common ; they 

 flow, at their beginning, over a surface covered with glacial matter and then sud- 

 denly pass beyond its limit of distribution and flow in channels through regions 



