20 CHICAGO ACADEMY OF SCIENCES. 



nounced than in either of the earher systems of the Early Wiscon- 

 sm sta,2:e. The undulations not infrequently extend back for 

 several miles on the inner border of the morainic system and fade 

 away gradually into oharacteristic till plain topography. 



Marseilles Morainic System. — The Marseilles morainic sys- 

 tem consists of a bulky ridge, usually with a single crest, but in 

 places double, which encircles the basin at the head of the Illinois 

 River, known as the Morris basin. From the north border of 

 the basin it extends northward along the east side of Fox River 

 to the vicinity of Elgin, beyond which it has not been separated 

 from the moraines of the Late Wisconsin stage. At its southeast- 

 ern end, also, this moraine is concealed by a moraine of the Late 

 Wisconsin stage. 



Aside from the main belt, called the Marseilles, there is a 

 small moFaine, the Minooka, wiliich separates from the Marseilles 

 moraine near Oswego, III, and passes southward into the basin 

 at the head of the Illinois. It has not been recog'nized south of 

 that stream. This moraine probably followed closely the Mar- 

 seilles moraine in its deposition, and is accordingly included in 

 the Marseilles system. 



The Marseilles moraine stands 50 to 100 feet above the plain 

 on its outer border and even higher above the basin on its inner 

 border. Its inner border relief is much more marked than that of 

 any of the morainic systems yet discussed. This is due largely to 

 the thinness of the drift deposits on. the inner border, there being 

 a much smaller amount of drift there tlian on the inner border of 

 the other morainic systems. 



The surface expression of this moraine is very similar to tliat 

 of the Bloomington system, tilie topography being of a sharply 

 undulating swell and sag type. The Minooka moraine is much 

 smoother surfaced than the Marseilles and has a relief scarcely 

 half as great. 



The structure of the drift, both in the Marseilles and the 

 Minooka moraine, is similar to tliat in the other morainic systems, 

 being chiefly a soft blue till. 



FIFTH INTERVAL SHOWN BY SHIFTING OF ICE LOBES. 



The evidence for thi^ interval is based largely on the change 

 of front or shifting in the position of the ice lobe which invaded 

 Northeastern Illinois and districts to the north and east. It is 

 best shown in Western Indiana, where the moraines of the later 

 stage cross those of the earlier one at a high angle. It is thouglit 



