346 THE ILLINOIS GLACIAL LOBE. 



Upon passing eastward from Lake County, Indiana, the several ridges 

 become combined into a single great ridge which admits of but little sep- 

 aration into distinct members in Porter and Laporte counties, Indiana, 

 and in southern Berrien County, Michigan. In northeastern Berrien 

 County two distinct ridges are developed, between which Pipestone Creek 

 flows in a southwestward course. Farther north the morainic system consists 

 usually of a main ridge on the eastern or outer border and ridges of more 

 or less definiteness near the western border, between which there are lower 

 tracts with gently undulating surface. 



The ridges jiist discussed, although bulky, are in places less impressive 

 topographic features than the knolls and basins which dot their surfaces. 

 They usually rise gradually from border to crest, and their dimensions can 

 be appreciated only by measurements with surveyor's level or other instru- 

 ments. The inner border in Porter and Laporte counties, however, usu- 

 ally shows an abrupt rise of 100 feet or more and portions of the inner 

 border in Michigan are also abrupt. Such is the case in the vicinity of the 

 St. Joseph River in central Berrien County, and at frequent intervals from 

 that river northward to the Kalamazoo River. 



Considerable variation in surface contour is displayed in each of the 

 States which this morainic system traverses. In the Illinois portion the 

 surface is usually gently undulating, with knolls 15 to 30 feet in height, 

 separated by winding sags and shallow basins. The trend of these knolls, 

 when on the crest and outer part of the morainic system, is usually about 

 in line with the trend of the ridges whose surface they occupy. Near the 

 inner border of the moraine, however, the knolls frequently show a tend- 

 ency to elongation at right angles with the trend of the morainic system. 

 The crest of the main ridge often rises abruptly 30 or 40 feet above the 

 remainder of the moraine in a narrow ridge or chain of knolls. In Lake 

 County, Illinois, there are numerous small lakes occupying the basins 

 among the morainic knolls. These range in size from a few acres up to 

 several square miles. Thev are usually shallow, a depth of 50 feet being 

 seldom attained, while the majority are but 10 or 15 feet. Among the lakes 

 there are knolls and irregular ridges rising 10 to 50 feet above the surface. 

 Some of the lakes are bordered by extensive marshes on one or more sides, 

 which were formerly probably covered by the lakes, for it is not rare to 

 find beaches a few feet above the present level of a lake. This morainic 



