316 



EARTH FEATURES AND THEIR MEANING 



poorly stratified, thick-bedded sands, gravels, and " worked over " 

 materials, and are believed to have been formed by subglacial 

 rivers which flowed in tunnels beneath the ice. Inasmuch as the 

 deposits were piled against the ice walls, the beds were disturbed 



at the sides when these walls disap- 

 peared, and the stratification, which 

 was somewhat arched in the beginning, 

 has been altered by sliding at both 

 margins. As already stated, eskers 

 have not a general distribution within 

 the glaciated area, but are often found 

 in great numbers at specially favored 

 localities. Formed as they are beneath 

 the ice, it is believed that many have 

 their materials redistributed so soon as 

 uncovered at the glacier margin, be- 

 cause of the vigorous drainage there. 

 They are thus to be found only at those 

 favored localities where for some reason 

 border drainage is less active, or where 

 the ice ended in a body of water. 



Drumlins. A peculiar type of small 

 hill likewise found behind the marginal 

 moraine in certain favored districts has 

 the form of an inverted boat or canoe, 

 the long axis of which is parallel to 

 the direction of ice movement, as is 

 that of the esker (Fig. 342). Unlike 

 FIG. 342. Small sketch maps the esker, this type of hill is composed 



Jze^pToportior^l^trLtt f tul > and fr m bein S f UIld in Inland 



tion of drumiins and eskers in it is called a drumlin, the Irish word 



meaning a little hill (Fig. 343) . Drum- 

 lins are usually found in groups more 

 or less radial and not far behind the 

 outermost moraine, to which their radiating axes are perpendicular. 

 The manner of their formation is involved in some uncertainty, 

 but it is clear that they have been formed beneath the margin of 

 the glacier, and have been given their shape by the last glacier 

 which occupied the district. 



Scale 



480 640 rods 



contour interval zo feet 



southern Wisconsin. The es- 

 kers are in solid black (after 

 Alden). 



