Contents

29 January 1988
Vol 239, Issue 4839

About The Cover

Prismatic rock columns of the Giant's Causeway, Northern Ireland, defined by a network of fractures formed during solidification and cooling of a basaltic lava flow. Nearly hexagonal columns in the flow interior have evolved from irregular tetragonal ones at the flow boundaries (not visible) by systematic changes in the orientation and spacing of column-bounding fractures as they grow inward. See page 471. [Atilla Aydin, Purdue University, West Lafayette, IN 47907]