10 



Indiana University Studies 



Where the stone has been split along a stylolite-partmg, 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 crv/.og 

 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, mth few ex- 

 ceptions, 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 paraflel 

 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 com- 

 monly parallel, or nearly so. 



Downward-penetrating stylolites are projections of the 

 overlying stratum and show the same lithologic character- 

 istics; while upward-penetrating stylolites bear the same re- 

 lationships with the underlying stratum (see Fig. 26). The 

 rock strata above and below a stylolite-seam appear undis- 

 turbed. 



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 stylolite- 

 seams varies from a few feet to several rods. Thus, stylolite- 



