Stockdale: Stylolites 



59 



Since the solution theory requires an actual removal of 

 rock material to an amount at least equal to the length of 

 the stylolites — sometimes as much as a foot, which would 

 mean that the rock strata had been reduced in thickness that 

 amount — one might expect a sag of the overlying rock strata 

 towards the center of the stylolite-parting, where solution 

 reaches its maximum. The occurrence of such a sag is rare 

 since stylolite-seams are so numerous and so distributed that 

 the amount of displacement of one seam is compensated by 

 that of an adjacent, underlying one. Such a phenomenon, 

 however, was noticed by the writer, especially in one locality, 

 a quarry of W. McMillan and Son, Reed Station district. 

 Here, the occurrence of stylolite-seams is less common than 

 usual. At the time of the writer's observation, a quarry face 

 exposed an entire stylolite-seam, grading at both ends into a 

 hardly noticeable line, and reaching a maximum thickness of 

 eight inches in the middle. A sag in the seam and the well- 

 laminated bed above it, equivalent to about eight inches (the 

 maximum amount of penetration), was distinctly noticeable. 



Relation of Stylolites to the Color of the Rock. The 

 difference in color of the Salem limestone presents some pe- 

 culiarly interesting relationships in the study of stylolites. 

 The sutures are frequently found at the contact of beds of 

 the blue and buff varieties of stone, in which case the columns 

 pointing in one direction will stand out in color contrast with 

 the adjacent ones (see Fig. 26). An interesting case is rep- 

 resented in Fig. 27 in which the blue and buff contact pre- 

 sents quite an irregular outline. Here, the irregular blue 

 parts of the upward-pointing columns are not continued into 

 the adjacent downward-penetrating buff columns. This phe- 

 nomenon involves a consideration of the origin of the two 

 colors of the stone. If the rock were all originally blue, 

 according to the generally accepted theory, the question arises 

 as to whether or not the irregular color change of the above- 

 figured example took place before, or after, the development 

 of the stylolites. It would appear that the stylolitic develop- 

 ment was subsequent to the color change — that the blue parts 

 of the underlying stratum have been actually removed and 

 are now occupied by the dow^n ward-projecting buff columns 

 of the overlying layer. If this was the case, the phenomenon 

 furnishes additional evidence that the stylolitic structures 



