. Corals and coral islands. Coral reefs and islands; Corals. STRUCTURE OF CORAL REEFS. 119 bours ; and in other parts it is very intricate, though throughout navigable by large vessels. The island of Upolu, of the Sa- moan group, is bordered by a reef nearly a mile wide on part of its northern shore ; but the waters within are too shallow for a canoe at low tide ; and therefore, notwithstanding its ex- tent, tlie reef is rather a fringing than a barrier reef. Within the green belt that mcircles Bolabola (p. 109) there is a large and deep channel navigable by ships. Beneath these channels lies,
. Corals and coral islands. Coral reefs and islands; Corals. STRUCTURE OF CORAL REEFS. 119 bours ; and in other parts it is very intricate, though throughout navigable by large vessels. The island of Upolu, of the Sa- moan group, is bordered by a reef nearly a mile wide on part of its northern shore ; but the waters within are too shallow for a canoe at low tide ; and therefore, notwithstanding its ex- tent, tlie reef is rather a fringing than a barrier reef. Within the green belt that mcircles Bolabola (p. 109) there is a large and deep channel navigable by ships. Beneath these channels lies, in general, the coral rock of the reef-region—the inferior part of the great reef formation whose. CORAL REEFS OFF THE NORTH SHORE OF TAHITI. upper portions constitute the so-called barrier and fringing reefs. The rock w^ould necessarily resemble that of the inner reefs already described ; but there should be a larger propor- tion of the white compact limestone made from the fine coral sands carried off from the higher reefs by the currents. Yet the bottoms of these channels are not always made up of calcareous or coral sands and fragments; for the volcanic or basaltic lands they adjoin are a source of ordinary mud ; and the river courses of the land and the tidal currents of the sea will often determine the nature of the bottom, or may cause in it alternate Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Dana, James Dwight, 1813-1895. London : Sampson Low, Marston, Low and Searle
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Keywords: ., bookauthordanajame, bookcentury1800, bookdecade1870, bookyear1875
