"A microrelief pattern of polygons 20 to 40 feet in diameter occurs in the perennially frozen ground of the glacierfree lowlands of the McMurdo Sound region, Antarctica. They are similar to ice-wedge polygons in the Arctic except that they are in ground devoid of vegetation and are outlined by textural changes in the soil between the inter-polygonal furrow and the enclosed polygonal areas. The term 'sand wedge' polygon is here proposed for this widespread phenomenon. . . . Suggested origin of the polygons and sand wedges is similar to the origin of foliated ice wedges and polygons in the Arctic. Periodic contraction cracks in the perennially frozen ground around McMurdo Sound, cracks produced by the great change in temperature from summer to winter, are gradually filled with clean sand which filters down from above in the spring and summer. Repeated cracking and filling with sand produces a wedge-shaped filling."