loO Wisconsm Academy of /Sciences, Arts, and Letters. 



the term lalco-silicious schist, although, perhaps, no better 

 single term can be used. It consists of thin laminations of 

 lalcosc material, separated by somewhat thicker layers of 

 >|uartzite, presenting a structure quite peculiar. Ii is neither 

 a typical schist nor a true slate. It lacks the cleavage of the 

 former and the homogeneity of the latter. It cleaves readily 

 along the laminte of talcose material, which, however, are not 

 entirely parallel, nor always continuous across the band. If 

 ^n oblique direction is found, it follows the talcose layer as 

 far as possible, when it passes by an abrupt transverse fracture 

 ^across the intervening quartzite layer to the next tolcose lami- 



J^Jiz 



A, Quartzite; BB, Talco-silicious schist; C, unexposed. 



i3se, and so continues by alternate cleavage and fracture, result- 

 ing in a step-like face. In this sharp distinction between 

 cleavage and fracture, the rock shows its relationship to the 

 irue slates. Were it demonstrably a true slate, the sugges- 

 -tions of this paper, now advanced with deference, would be 

 stated as a deraonstratioQ. It is the "foliated" structure of 

 some authors, but the foliations are not parallel to the bedding 

 lines. 



In the formation on the east side of the lake, the lamina- 

 tions cross the band at an average angle of 27^", having thus a 

 dip of 42° to the north. (See figure.) On reaching the quart- 



