132 Wisconsin Academy of Sciences^ Arts, and Letters. 



But the fact of upheaval bears its own evidences of pressure. 

 Over all this area, the rocks have been tilted northwards till 

 they dip at angles varying from 15" to 90°. Similar outcrops 

 elsewhere in the state present like phenomena. The common 

 cause of tilting throughout the globe is lateral pressure, and no 

 other cause seems competent in the present case. The same 

 is true of metamorphisra, though in a somewhat less degree. 

 The two are usually synchronous events having a common 

 cause. The lateral force usually acts from the direction of the 

 neighboring ocean. This would require, in the present case, 

 a force acting from the south. Let such be assumed to be the 

 case. While the beds were horizontal, the force would tend 

 to produce compression, heat and metamorphism, and as the 

 strata oifer the greatest resistance in this position, these results 

 must be supposed to be greatest at this stage. The result of 

 compression would be cleavage in such portions of its rock as 

 were capable of taking it in a direction transverse to that of the 

 force, according to the law of slate formation. The more re- 

 sisting quartzite would prevent the complete compression of 

 the more yielding schistose material. This is substantiated by 

 the observations of Mr, Sorby. But as the strata yielded, the 

 force would take a new direction relative to the layers and ex- 

 pose the schistose material to farther compression, producing 

 new foliations in a new direction, and those previously exist- 

 ing would be modifed. And so for every change in the strata 

 till the force ceased to act. This is precisely the phenomena 

 presented by the case in hand. Some of the features of what 

 is known as " drag " in slate are unmistakable. 



A line drawn perpendicular to the laminae should, if this 

 reasoning be true, represent the direction of the upheaving 

 force. A line so drawn would be transverse to the shore of 

 the Eozoic island to the northward, and precisely in the di- 

 rection demanded by theoretical considerations. 



The fact that the foregoing explanation is so fully in har- 

 mony with the usual phenomena of upheaval and metamorph- 

 ism is at least an element in its favor. 



