Stockdale: Stylolites 



53 



sistance, stylolitic interteething would not result. Continued 

 solution would give only a slightly undulating seam, with a 

 residual clay parting (see Fig. 20). Such seams are found. 

 They sometimes continue for several yards, with perhaps an 

 occasional, sharply protruding column (perhaps several inches 

 in length) , or a series of columns, where the rock offered suf- 

 ficient difterential resistance to solution to produce such (see 

 Fig. 21). 



Converging and pointed penetrations might result where 

 the difference in resistance to solution on the two sides of the 

 crevice is little and is less than that in the case of columns 

 with parallel sides. Altho most of the solution is confined to 

 the ends of the columns where the pressure is greatest, the 

 side-surfaces might be more or less attacked. Since the end 

 represents the first and oldest portion of the columns, the 

 portions nearer the end, because of their longer existence, 

 would be longer exposed to the attack of whatever solution 

 might take place on the sides, and would thus become gradu- 

 ally narrowed, giving converging or pointed columns. Dy- 

 namic, lateral pressure upon the rock would promote further 

 solution of the sides. Wagner emphasized this point in ex- 

 plaining pointed penetrations. 



The writer would explain curved, or bent, stylolites as a 

 result of the columns, during their growth, striking an espe- 

 cially resistant part at an angle (the resistance being suffi- 

 cient to overcome the effect of the overlying pressure upon 

 vertical solution) and consequently being deflected to one 

 side, following the line of least resistance. The occurrence 

 of such is an exception among Indiana stylolites. The writer 

 observed a few cases where the bending of the column had 

 been sufficient to fracture it. Wagner explained curved stylo- 

 lites as resulting from ''complicated pressure and solution 

 factors" and gave examples where the fractures on the con- 

 cave sides had been filled with gypsum (Wagner, 1913, p. 

 118). 



With the exception of the few cases of curved stylolites, 

 the direction of penetration is parallel with the direction of 

 pressure, and the plane of solution is usually at right angles 

 to it. In undisturbed strata, void of lateral, djaiamic pres- 

 sure, the pressure is static, resulting from the weight of the 

 overlying sediments ; the stylolites are vertical, and the stylo- 

 lite-seams, horizontal. Such is the usual case in the Indiana 



