. Elements of geology : a text-book for colleges and for the general reader. Geology. 148 ORGANIC Fig. 118. coral platform is indicated to the eye of the observer by a white sheet of breakers which surrounds the island like a snowy girdle, and ex- tends some distance from the shore-line (Fig. 117). The section Fig. 118 will give a clear idea of the contour of land and sea bottom. In this and the fol- lowing sections the dotted parts represent coral formation. If the island is large, and considerable rivers flow into the sea, breaks in the reef plat- form will occur oj)posite the mou
. Elements of geology : a text-book for colleges and for the general reader. Geology. 148 ORGANIC Fig. 118. coral platform is indicated to the eye of the observer by a white sheet of breakers which surrounds the island like a snowy girdle, and ex- tends some distance from the shore-line (Fig. 117). The section Fig. 118 will give a clear idea of the contour of land and sea bottom. In this and the fol- lowing sections the dotted parts represent coral formation. If the island is large, and considerable rivers flow into the sea, breaks in the reef plat- form will occur oj)posite the mouths of the rivers, the corals in these places being destroyed by the fresh, muddy waters. In the case of fringing reefs no islands are formed by the action of waves, but only a shore-addition to the original island, as shown at a a in the section. Barrier Reefs.—In many cases besides the fringing reef there is another reef surrounding the island like a submarine rampart at the dis- tance of from ten to fifty miles. As the reef rises nearly to the surface of the sea, its position is indicated by a snowy girdle of breakers sur- ___^ rounding the island at a distance, and this snowy girdle is gemmed with wave- formed green islets. Within this girdle, and between the rampart and the island, there is a ship-channel twenty or thirty fathoms deep (Fig. 119). Through breaks in the coral rampart ships enter this channel and find secure harbor in a stormy sea. The section Fig. 120 will give a clear idea of the conformation Fig. 120. of bottom. On the landward side of the coral rampart the slope of the bottom is gentle, but on the seaward side it is very steep, so that it is almost unfathomable at a short distance from the reef. Circular Reefs, or Atolls.—These are the most wonderful of the reefs of the Pacific. In a circular reef there is no volcanic island or other visible land to fig. Please note that these images are extracted from scanned page images that may have been digi
Size: 3625px × 690px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1892
