THE VALPARAISO MORAINIC SYSTEM. 353 



sunk 30 to 40 feet or more below the general level of the plain. The St. 

 Joseph River is bordered by broad gravelly terraces 2 miles or more in 

 width from the inner border of the moraine southward a short distance 

 beyond Berrien Springs. From this point up to Buchanan the moraine bor- 

 ders the valley closely on each side. Above Buchanan the river is again 

 bordered by gravel terraces which are cut in the gravel plain that was 

 formed on the outer border of the moraine. 



THICKNESS OF THE DRIFT. 



Situated as the Valparaiso system is, in a district over which there 

 have probably been several successive ice advances with intervening 

 recessions, the drift can scarcely be supposed to belong solely to the 

 advance which formed this morainic system. It is known that remnants 

 of the sheets of the Illinoian and Iowan drift are present in northeastern 

 Illinois and northwestern Indiana. There is also present a considerable 

 amount of drift of the early Wisconsin series. The early Wisconsin drift is 

 so similar to that of the Valparaiso drift sheet that it is doubtful if it can be 

 readily distinguished or separated from it. There does not appear to be a 

 well-defined soil horizon at the base of the Valparaiso sheet to mark the line 

 of junction, such as occurs under wide areas at the base of the early Wiscon- 

 sin drift. The thickness of the Valparaiso drift sheet can perhaps be best 

 estimated by the relief, for it can scarcely be assumed to exceed greatly 

 the measure of the outer-border relief of the moraine, except in places 

 where there is a great gravel filling on that border. The gravel filling is of 

 little consequence on the outer border of the Valparaiso morainic system in 

 Illinois and in Lake and Porter counties, Indiana. Farther east and north 

 it is of considerable depth. The relief in the Illinois portion is estimated to 

 average about 65 feet. The average thickness of the Valparaiso sheet is 

 probably somewhat less than the relief, since the sheet is markedly thinner 

 on the borders of the morainic system than along its main crest. 



In southwestern Michigan it is difficult to determine whether the early 

 Wisconsin sheets are present in large amount. A fresh drift of great depth 

 is found along the line of the morainic system and westward from it to the 

 borders of Lake Michigan. In all probability the thickness of the Val- 

 paraiso sheet is as great in southwestern Michigan as in northeastern Illinois 

 and northwestern Indiana, and it may be even greater. 

 mos xxxviii 23 



