224 Frank Cramer — Recent Rock Flexure. 



Although the layers were still in position and presented 

 smooth joint faces, the rock, for a distance of about two feet 

 back from both faces of both 

 seams, was splintered by a 

 large number of small fract- 

 ures parallel to the plane of 

 bedding (fib, fig. 4). The 

 faces of these fractures, like 



those of the joints, were rusty Fig. 4. Section of anticlinal at Kaukauna, 



from the decomposition of Wls - 



pyrite. When this part of the rock was broken w T ith a ham- 

 mer, at the time the layers between the joints were removed, 

 the hammer rebounded as usual when the rock was struck 

 from one direction, but failed to rebound when the rock was 

 struck at right angles to that direction. When it broke it 

 shivered into small pieces. 



Evidently a steady and long-continued pressure was brought 

 to bear on the faces of the joints until the layers between them 

 were bowed up and the ends had undergone the preliminary 

 fracturing. And the pressure ceased or the rock was removed 

 just before the crisis came ; everything was ready for the pro- 

 duction of another " line of fracture and crushed rock/' If 

 this is the explanation of the condition of the rock along and 

 between the joints, the theory of pressure of superincumbent 

 mass is inapplicable, for the axis of the disturbances in this 

 case *is at right angles to what the theory calls for. But this 

 axis is parallel with the axes of the fractures and folds at the 

 Combined Locks. The two sets of phenomena are less than 

 two miles apart, and the case at Kaukauna seems to be simply 

 a stage through which the rock at the Combined Locks had 

 already passed. They are so intimately connected that a com- 

 mon cause for all of them must be sought. The movements 

 were without doubt all produced by slowly applied and long 

 continued lateral pressure. But if the movements were super- 

 ficial, as there seems to be some reason for believing, a super- 

 ficial cause must be sought. 



It would be difficult to assign a cause from the study of 

 these cases alone ; but it seems reasonable to class them with 

 similar ones observed in other parts of the country. Mr. G. 

 K. Gilbert has propounded a suggestive theory in explanation 

 of phenomena in many respects similar to those presented here.* 

 He believes that sufficient lateral pressure to account for them 

 has been developed in post-glacial times, from the expansion of 

 the superficial strata resulting from the rise in temperature 

 after the disappearance of the ice. This theory has still to be 



* See this Journal, vol. xxxii, p. 324 ; and Proceedings of A. A. A. S., 35th. 

 meeting, p. 227. 



