stratum into the downward-pointing penetrations, and the presence of horizontal lamination in the adjacent, upwardprojecting columns.

Often dark laminae stand out very clearly in the stratification. Where penetrated by stylolites, they are missing (see Figs. 23 and 24). Under the pressure theory one should expect to find them displaced above or below the ends of the penetrating columns. Such is not the case. How could the various, above-described laminated conditions have been retained, had the sediments been "differentially compressed in a plastic state"? The rock materials have been actually re

FIG. 25.-Diagram of a small stylolite-seam partially eradicated by the penetration of upward-pointing columns of a large stylolite-seam. Mitchell limestone. One-third natural size.

moved, and the two beds have been "dovetailed" into each other.

Analogous to this observation of the removal of the laminae of the one bed into which the columns of the opposite have penetrated, are numerous examples of small styloliteseams which have been penetrated and removed by larger stylolites. Figure 25 is a case where a small, once-continuous stylolitic suture, following the lamination of the rock, occurs now only in the downward-projecting columns, being sharply cut off and absent in the rock of the upward-pointing parts. Under the pressure theory, should not one expect to find it displaced in the rock above the columns?

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 welllaminated 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 peculiarly 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 represented in Fig. 27 in which the blue and buff contact presents 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 phenomenon 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 abovefigured example took place before, or after, the development of the stylolites. It would appear that the stylolitic development was subsequent to the color change that the blue parts of the underlying stratum have been actually removed and are now occupied by the downward-projecting buff columns of the overlying layer. If this was the case, the phenomenon furnishes additional evidence that the stylolitic structures

FIG. 26.-A typical, large stylolite-seam in the Salem limestone of the Dark Hollow district, Lawrence County, Ind. Note the irregularity in length and width of the interpenetrating parts. The darker, upper stratum is blue stone; and the lower, buff. Note the small, minor stylolite-seam running across the column below X. The clay parting is plainly visible. The upper and lower strata are distinctly lithologically different. The longest column is about 9 inches.

were formed after the hardening of the rock, since the alteration of the buff stone from the blue is in itself (according to the theory) a feature which occurred since the consolidation of the rock. Observations of the above nature are not uncommon in the Salem limestone. It has been suggested, however, that the above-described color changes of alternating columns could have occurred since the development of the stylolites, altho evidence appears to be against it.

FIG. 27.-Semi-diagrammatic sketch of stylolites in the Salem limestone, showing blue (shaded) portions of the lower stratum penetrated by buff columns of the upper layer. One-third natural size.

RELATION OF STYLOLITES TO FOSSILS. Careful observations of Indiana stylolites show the presence of fossil caps to be an exception. This fact alone precludes Marsh's theory in which the fossil caps were an essential feature. The former assumption that each column has a shell at its end was no doubt a prejudiced one. Stylolitic phenomena are just as numerous in the non-fossiliferous, even lithographic, strata as in the highly fossiliferous ones. Only a few cases have been observed by the writer where the outline of the stylolite was determined by the presence of a fossil covering. Frequently, however, the stylolite ends are partially covered

by a shell. The presence of a shell covering might, no doubt, favor the formation of the columns, the shell often being more resistant to solution than the opposite rock mass. Shell coverings, when present, often show distinct signs of corrosiona distinct evidence in support of the solution theory. Wagner's investigations of the Muschelkalk stylolites revealed the frequent occurrence of fossil coverings which determined the shape of the columns. The fossils of the Muschelkalk, however, are much larger than those of the Indiana limestones. Wagner treats of the subject in much detail (Wagner, 1913, pp. 119-121).

Brachiopod

FIG. 28.

Example of a brachiopod shell partially penetrated by a column of a small stylolite-seam. Mitchell limestone. Two times natural size.

FIG. 29.-Mussel shells pierced by stylolites. (After Wagner.)

The smoothness and sharpness with which the edges of stylolites are cut is striking. Close inspection of the columns shows that the hundreds of fossils, oölitic grains, mineral crystals, etc., have been sharply smoothed off at the contact of the sides of the penetrations. The missing remains are not to be found. The lower, coarsely fossiliferous portion of the Harrodsburg limestone reveals many examples of this, and microscopic examination of the fine-grained Salem limestone gives an abundance of distinct evidence. Above or below the stylolite-seams are often found remains of brachiopods, gastropods, bryozoans, etc., which have been pierced, or