102 . THE MICHIGAN ACADEMY OF SCIENCE. 



What little is known here of the earlier drift sheets is obtained from 

 borings and from certain constituents of the drift. 



At the margin of glaciers are ridges of earth and stones called mo- 

 raines made up from material brought by the ice to its edge or place 

 of melting. In the mountain glaciers these ridges are commonly but a 

 few yards in width. Those formed by the great ice fields of North 

 America and Europe are much larger, the width ranging from a mile 

 or less up to several miles, and the height from about 25 feet up 

 to nearly 500 feet. The surface is ordinarily very uneven, with knolls 

 and interlocking ridges among which basins are inclosed. But from 

 this sharp expression the surface of the moraine, often grades into 

 a nearly featureless smooth ridge. The Wisconsin drift carries a more 

 complex series of moraines than the older drift sheets, and the portion 

 of the Wisconsin drift in Michigan has perhaps greater complexity than 

 is to be found anywhere else in the United States. It is the moraines 

 with their included lakes that give the southern peninsula much of its 

 picturesque scenery. 



The moraines just described are commonly called terminal moraines, 

 while the portion of the drift sheet between the ridges is sometimes 

 termed the ground moraine, but more commonly the till plain. 



The till plains are often diversified by ridges called drumlins, which 

 lead toward the terminal moraines. Some of the ridges have a form 

 similar to an inverted canoe with a remarkably smooth and regular 

 surface. They are 10 to 100 feet or more in height, and from a frac- 

 tion of a mile to about two miles in length, while the width is a third 

 to a tenth that of the length. The name drumlin applied to these ridges 

 in Ireland has been commonly adopted in this country, though they are 

 frequently referred to as lenticular hills. They are composed very 

 largel}' of a thoroughly kneaded mass af till which lias the appearance 

 of being built uj) by slow accretions, as if contributed by a partially 

 checked current of dirty ice, the action being similar to that of water 

 in building a sand bar. Drumlins are not widely developed in Michigan, 

 though they abound between Grand Traverse and Little Traverse Bay. 



Kidges of another class, that lead toward moraines, are called "hog 

 backs'' by persons not versed in geology, but geologists term them esk- 

 ers or osars, applying terms by which they are known in Scotland and 

 Scandinavia. They are narrower and sharper and have a more irregu- 

 lar surface than drumlins, and are composed largely of sand and gravel. 

 They appear to be the product of streams of water that Avere flowing 

 through or under the ice toward its margin. Eskers are more widely 

 distributefl in Michigan than drumlins. but are most conspicuous in the 

 district south and southeast of Lansing. 



The plains between moraines occasionally carry sharp knolls or clus- 

 ters of knolls of gravelly constitution which have received the Scotch 

 term kanie. This name is also applied to sharp knolls of gravel which 

 occur in moraines that are not otherwise very gravelly. These knolls 

 apparently are due to stream accumulation, but the manner of building 

 up is not clearly understood. They are of fre<iuent occurrence in all 

 parts of the lower peninsula. 



The plains which border the Great Lakes carry low ridges of gravelly 

 material, representing the beaches of lakes, which stood at higher levels 

 than the present water bodies. They are as a rule only five to fifteen 



