218 GEOLOGY OF EASTERN WISCONSIN. 



of coarser material. This action took place in part simultaneously with 

 the formation of the deposit, and so these rearranged and stratified 

 beds, mingle irregularly with the unsorted material. Taken as a class, 

 this constitutes the original glacial deposit or ground moraine, and 

 in this report it is known by its most characteristic feature, Bowlder 

 Clay, or by the term Till. 1 That portion of the bowlder clay which 

 antedates the formation of the Kettle Range merges into that forma- 

 tion, and on the opposite side, a precisely similar deposit of bowlder 

 clay takes its origin from the great moraine and spreads over the re- 

 maining area of the district, although overlaid in part by subsequent 

 formations. So it appears that the Kettle moraine is simply a pecu- 

 liar and irregular aggregation of this wide-spread ground moraine. 

 In relative age then, a portion of the Bowlder Clay is older than the 

 Kettle Range, and a portion, more recent, there being no essential dis- 

 tinction in character between the two parts. 



If we descend to a more special and critical examination of the 

 material of this formation, the clay, the chief element, will be found 

 to be of the most heterogeneous character. The prevailing color i s 

 blue, but it is not unfrequently reddish, greenish, earthy brown, or 

 ashy. In texture, it varies from that which is highly plastic and ad- 

 hesive to varieties so arenaceous and friable as scarcely to cohere in 

 lumps. In general, however, it is intermediate between these ex- 

 tremes, being marly in character. The imbeded bowlders are of all 

 sizes from those that weigh many tons downwards, and are as various 

 in character. A large proportion of those at any given point are 

 usually from the subjacent rock, or from some formation in the im- 

 mediate vicinity, but there is usually present, a large proportion of 

 Archaean erratics. Along the lake shore there are many bowlders that 

 represent various formations newer than any known to exist in Wis- 

 consin, having doubtless been derived from the basin of the lake, or 

 from Michigan. 



These bowlders show every degree of erosion. Some have not only 

 been thoroughly rounded but have suffered much reduction in size, 

 as is shown by the projection of the harder and more unyielding por- 

 tions, giving the specimen often a unique and fanciful form. Some 

 specimens are polished and striated on one side, but rough and an- 

 gular on the others, due doubtless to their having been firmly im- 

 bedded in the under surface of the glacier, and so polished as they were 

 forced along over the rocky surface below. Other fragments are al- 

 most wholly unmodified, though often of soft and fragile material. 



1 See The Great Ice Age, by James Geikie, 1874. 



