stylolite

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A secondary structure found along contacting surfaces of adjacent calcareous rock layers, the contact zone appearing in cross section as a series of jagged interlocking up-and-down projections that resemble a suture or the tracing of a stylus.

from The Century Dictionary.

• noun A peculiar form of jointed or columnar structure occasionally seen in beds of limestone, unting the adjoining surfaces of two layers of the rock, and usually from half an inch to 3 or 4 inches in length.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun geology An irregular surface between strata consisting of toothlike projections; most common in limestone and dolomite.