208 



in diameter, and the separate blocks have been recemented by material of 

 the same sort that composes the substance of the rock. The cause is 

 not obvious, but the phenomena is certainly not referable to uplift and 

 disturbance. It seems more probable that if we were able to trace out 

 the history we should find some modification of the force that produces 

 joints, whatever it may be, as the cause of the phenomena we are 

 considering." 



The high angle stylolite planes of the interior conformation of the 

 cones is another feature which should be considered in connection with 

 the brecciated structure. The columnar part of the stylolite seam is pe- 

 culiar in having its axis lie parallel with the separation plane, and seems 

 to show that the columnar structure is the result of a downward move- 

 ment of the overlying layer. At the StaufHer quarry, two miles west of 

 South Wabash, and at Rockyway Oreek the angle of the separation planes 

 does not exceed 25 degrees, and it is probable that they may be modified 

 bedding planes, something like those described by Mr. T. C. Hopkins iu 

 his report, of 189G, on the. Bedford oolitic limestone of Indiana. 



The exposures at Staufller's and Rockyway also show that the picket 

 rock gradually changes into even bedded quarry stone, and that the picket 

 rock is a modified form of the othei*. At the same time the dip changes 

 from an angle of 25 degrees to neai'ly horizontal. 



The high angle stylolite planes are too nearly vertical to have been 

 the result of sedimentation. They evidently grow out of a number of 

 conditions. Briefiy, the picket rock cones and ridges rest on a core or 

 axis of cement rock or shale, the latter being the result of erosion. It 

 is probable the layers of stone, overlying the core, were of continuous 

 thickness when deposited, and that the brecciated character and stylolite 

 planes are the result of pressure and unequal resistance to a downward 

 shear. 



A somewhat similar system of brecciated and irregularly bedded stone 

 extends from the interior of Ohio, across Indiana and into Illinois. 

 Through Indiana and in the vicinity of Chicago high angle sty'.ollte planes 

 are a marked feature of the exposures. In Ohio the distorted bedding is 

 referred to the Waterline formation. In Indiana similar ii'regularities are 

 supposed to be confined to the Niagara group beds. Dr. A. J. Phinney 

 has been the only Indiana geologist to dissent from this opinion by assign- 

 ing the Delphi and much of the Logansport exposures to the Dower 

 Helderberg. Prof. Orton, in his report on the Ohio and Indiana gas field. 



