FIG. 1. Stylolites in the Muschelkalk, showing striated sidesurfaces and clay caps. From Rüdersdorf, near Berlin. Original in Marburg Museum. (From Kayser's Lehrbuch der Geologie.)

FIG. 2.-Large, perfectly formed stylolites of the Salem limestone. Note the slicken sided side-surfaces and the clay caps of the columns. One-sixth natural size. From a quarry of the Consolidated Stone Company, Dark Hollow district, Lawrence County, Ind.

FIG. 3. Typical, jagged stylolite-seam in the Salem limestone. From a quarry of the Consolidated Stone Company, Dark Hollow district, Lawrence County, Ind.

FIG. 4.-Small stylolite-surface in the Salem limestone, show

ing the characteristic roughness which, in itself, has the physical appearance of solution. The white portions are broken-off stylolites; the black, residual clay.

Where the stone has been split along a stylolite-parting, an extremely irregular, pinnacled surface is presented (see Figs. 4, 5, and 6). The term "stylolite-surface" might well be applied to such. The term "stylolite" (from the Greek σTV205 meaning "column") applies to each individual, penetrating column. Thus it is seen that a stylolite-seam is made up of many stylolites whose direction of penetration, with few exceptions, is at right angles to it.

Stylolites are always characterized by two principal fea

tures:

1. An ever-present clay cap which comes to rest at the end (see Figs. 1, 2, 6, 11, and 26).

2. Parallel fluting, or striations, on the sides (see Figs. 1, 2, 5, 11, and 34).

The clay cap is usually thin, varying in thickness with the length of the stylolite and the composition of the stone. The caps of very small stylolites are mere films; those of long stylolites are sometimes as much as one-half inch or more in thickness. The stylolites of impure limestones and dolomites bear thicker caps than those of purer stone. The color of the cap varies usually from brown to black.

The fluting on the sides of stylolites often resembles the slickensides of fault planes. These striations are parallel with the direction of the penetration of the stylolites. The sides of the columns are usually slightly discolored with a thin film of clay. The sides often converge, but are commonly parallel, or nearly so.

Downward-penetrating stylolites are projections of the overlying stratum and show the same lithologic characteristics; while upward-penetrating stylolites bear the same relationships with the underlying stratum (see Fig. 26). The rock strata above and below a stylolite-seam appear undisturbed.

Stylolite-seams usually begin as a barely noticeable, smooth crevice or suture, grading from a slightly undulating seam into a finely toothed crevice-the teeth gradually increasing in size until typical stylolites appear (see Fig. 16). The stylolite-seam at both ends grades out into a fine suture which gradually disappears in the hard rock. The length of styloliteseams varies from a few feet to several rods. Thus, stylolite

partings are sometimes several square rods in area. Some partings are so small, however, as to have an area of only a few square feet. Single, isolated stylolites are never found. They occur only as a series of alternating columns making up a stylolite-parting.

Stylolite-seams run most commonly in a horizontal direction, or nearly so, and parallel with the lines of stratification. Occasionally they have been observed running obliquely and even perpendicularly (see Fig. 17). They are also known to

FIG. 6.

Stylolite-surface in the Mitchell limestone, showing the thin deposit of black residual clay. The white spaces result from broken-off stylolites, and show the irregular outline of the columns.

cross one another. The chief characteristics of the stylolites are the same regardless of the direction of the seam.

Stylolite-partings are often very numerous and close together (see Figs. 16 and 32). In a single, thin stratum, there have been observed as many as a dozen or more lying directly one above the other with only a few inches of stone separating them. They have also been observed to lie one upon another and even to penetrate one another. In some stylolite-bearing strata, however, the partings are very rare and far apart.