THE SHELBYVILLE MORAINE. 195 



than 700 feet, while at the river bluff it is about 650 feet. Between the 

 Sangamon River and Peoria the highest points along the crest are about 

 800 feet, and the crest seldom falls below 700 feet. Near the east bluff of 

 the Illinois, at Groveland, the altitude is 785 feet, or more than 350 feet 

 above the Illinois River; but in the northeast part of Peoria the moraine 

 appears on the west bluff of the river at an altitude scarcely 200 feet above 

 the stream. Passing northward the moraine soon rises to a height of 800 

 feet and stands near this elevation throughout its course in northern Peoria 

 County and in eastern Stark County to where it is overridden by the 

 Bloomington moraine. 



SITRFACE CONTOURS. 



Although this moraine constitutes the margin of a thick sheet of drift 

 and has usually considerable relief on its outer border, it presents in general 

 a comparatively smooth surface, sharp knobs being developed only at a few 

 points, and swells or undulations of the surface being of a gentle, unobtru- 

 sive type. In places it has no more undulation than has the plain north of 

 it. Were one not aware of the great relief above the outer-border district 

 and certain that this relief is due entirely to the presence here of a sheet 

 of drift not found in the outer-border district, one might well question the 

 propriety of considering this a morainic belt. But these criteria place 

 beyond question the termination of the ice invasion along this line, and no 

 better term than moraine seems applicable to such a thickened drift ter- 

 minus. In this connection it may be remarked that where there is an 

 attenuated drift border at the margin of the glaciated district, the term 

 glacial boundarv seems preferable to moraine, but in the case of the margin 

 of a later drift sheet which lies back some distance from the glacial bound- 

 ary it would seem necessary to substitute some definition or explanatory 

 term. In case the later drift sheet under discussion should have an attenu- 

 ated border the term moraine scarcely seems applicable, and it would be 

 preferable to substitute the term Wisconsin boundary, but if the drift sheets 

 have a thick edge and bold relief, as is generally the case, the term moraine 

 seems applicable even though no sharp morainic contours are present. As 

 it is, however, a portion of the margin of this drift sheet presents charac- 

 teristic morainic features, and these features pass, by insensible gradations, 

 into the more nearly plane portions of the border. To set forth fully the 

 topography of this border a somewhat detailed description is necessary. 



