The formation of stylolite seams occurs title to the plastic nature of calcareous sediments and during the early period of their consolidation. Stylolitic development has no part in the process of removing petroleum products from calcareous source beds. The disconnected contraction cavities formed along stylolite seams may entrap petroleum in much the same manner as disconnected contraction cavities in dolomitic limestone as described specifically in connection with the Little Falls, N.Y. dolomite. When the contraction cavities are sufficiently large, numerous, and connected in the source beds, most of the petroleum may be expected to escape, under the right conditions. On the other hand, if such cavernous beds are structurally suitable they may hold the original oil or they may receive and retain migrating oil in large quantities especially if access channels exist.