National Geographic : 1957 Jan
Marbled Shallows * Lay a Mosaic About Wooded Heron Island Like an iceberg, most of the Great Barrier lies underwater. Only reefs and jungled heaps of coral sand betray the stupen dous mountain of coral beneath. Borings on Heron have disclosed antique coral 450 feet thick. The Barrier covers some 80,000 square miles (map, page 7). Twelve miles across at the nar rowest, the platform extends about 150 miles at its widest point before plunging thousands of feet to the abyss. Between mainland and outer reef, the lagoon is cluttered with hun dreds of islands and outcrop pings, and threaded by tortuous channels. This waterway, sel dom more than 150 feet deep, sits on top of the reef. Most of the islands are un inhabited save by occasional pearlers, fishermen, and light house keepers. Heron supports a marine laboratory and accom modations for holiday visitors. + Blankets thrown over heads shut out the glaring sun as sightseers study Heron's reef through a glass-bottom boat.