116 



All are elongated in the direction of the group of which they 

 form a part ; and thus a series of Atolls, forming an Archipelago, 

 would be but the translation to the surface, so to speak, of the 

 submarine land which support the Atolls themselves. 



K Barrier reefs and Atolls indicate great ai-eas of subsidence. 

 Fringing reefs, bordering the shores of emerged lands, are 

 often stationary, or give evidence of a slow and gradual elevation 

 of the continent they fringe . In the islands of Mauritius, Bourbon, 

 Timor, and New Guinea ; in the Mariana Isles, the Sandwich 

 Archipelago, and other Fringing regions, there has been a 

 modem elevation of the land, as proved by beds of recent 

 shells in raised beaches, which the highest tides do not now 

 attain. The shores of the Eed Sea have* experienced similar 

 elevatory movements, followed by a movement of depression ; 

 and many of the Friendly Isles are but ancient Atolls, that have 

 been submitted to oscillations of the same kind. The Keys of 

 Florida, and the Great Eeef itself^ attest the slow growth of the 

 Coral formation in this part of the peninsula; and the gradual 

 rise of the same to form new land in this region has been 

 already fully explained. Fringing reefs, therefore, shew that 

 the shores which they skirt are stationary or rising; whilst 

 Atolls and Barrier reefs attest that subsidence has taken place. 



If we examine attentively the map coloured by Mr. Chakles 

 Darwin, shewing the geographical distribution of the different 

 kinds of Coral reefs, we become impressed with the vastness 

 of the areas occupied by reefs and islands of Coral formation, 

 none of which rise to a greater height above the level of the 

 ocean than that attained by matter thrown up by the winds and 

 waves of an open sea. In the Pacific Ocean there is a band of 

 groups of Atolls, which, measuring from the south end of the 

 Low Archipelago to the northern termination of the Marshall 

 islands, is 4500 statute miles long, and varying from 200 to 600 

 miles broad: to this may be added the Carohne and Pelew 

 Archipelagoes, stretching more than another 1000 miles to the 

 westward. The great Barrier reefs on the north-east coast of 

 AustraKa are 1250 statute miles in length, and from 10 to 90 

 miles in width. The Laccadive, Maldiva, and Chagos groups. 



