MICHIGAN ACADEMY OF SCIENCE. 37 



to a uniform height and if the valleys and channels between them were 

 filled a nearly horzontal plain would be produced. The depressions 

 separating the drumlins are in many instances, smooth-surfaced, con- 

 cave troughs; and in one example there is a well defined trench of this 

 character, about 12 feet deep and from 20 to 30 feet wide, about the 

 N. E. end of a small drumlin and extending along its sides. The surfaces 

 of the drumlins to a depth of some 12 to 18 inches, are composed of 

 exceedingly fine, dust like loam}' sand, which contains loose stones and 

 boulders. 



The drumlins are for the most part smooth-surfaced, half cigar-shaped 

 hills of the normal type, but in a few instances instructive irregularities 

 are present. Among these are : A flattening of a portion of the normally 

 elliptical ground-plan, as if a marginal portion of a well-shaped drumlin 

 had been removed by erosion, leaving an abnormally steep slope; deep 

 transverse trenches at right angles to their longer axes; straight or 

 curved trenches extending from their summits down their sides; irregular 

 pits in their normalh' smooth surfaces; and in one instance a terrace-like 

 shelf with a convex longitudinal profile, parallel with the crest line of 

 the drumlin on the side of which it occurs. 



In the valleys between the drumlins there ae several eskers which as 

 a rule are in a general way parallel with their longer axes, but in a few 

 instances cross their trend nearly at right angles. In one example an 

 esker extends each way from a transverse trench in a drumlin ; and in a 

 few instances eskers occur on the tops of drumlins. 



From the evidence just summarized, the conclusion is drawn that the 

 drumlins of the Menominee area were produced by ice erosion from a 

 previously deposited till sheet. This explanation is essentially in har- 

 mony with the theory of the origin of drumlins advanced several years 

 since by Professor Shaler. 



Attention will also be invited to the importance of ice erosion in 

 shaping the t0])0gTaphy of glacial deposits in other regions. 



Ann Arbor, Mich. 



