246 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



polyp, the thicknesses and areal dimensions attained in virtue 

 of the continued upward growth and seaward extension of the 

 reef, and the proportion of coral formations in the limestone 

 and dolomite rocks of the Alps and other regions. 



Reinhold Forster, who accompanied Captain Cook on his 

 voyage round the world in 1778, expressed the view that the 

 formation of coral reefs was limited to the seas of warm 

 climates, and wrote as follows regarding the mode of construc- 

 tion : " The reef is built up by the lithophyte worms from the 

 ocean-floor until it comes within a very small distance of the 

 surface of the ocean. The waves wash against this newly-built 

 wall all kinds of debris, mussel shells, fronds of sea-weed, 

 fragments of coral, sand, and other material, so that the sub- 

 marine coral wall gradually increases in height, and begins to 

 be seen above the surface." 



The circular form of atoll reefs is explained by Forster as 

 the result of a continued effort on the part of coral polyps to 

 erect a wall protecting them from dominating winds. James 

 Cook added a number of observations on reef-growth, supple- 

 mentary to those of Forster; and John Barrow in 1806 made 

 the first attempt to determine the thickness of coral rock on 

 an island. Flinders prepared in 1801 a map of the reefs off 

 the Australian coast, and in 1814 published an important 

 cartographical work, in which he agreed with Forster's views 

 on reef-growth. Peron in 1816 enumerated 245 islands of 

 reef-coral, and determined their geographical position between 

 34 north and south latitude. 



Valuable observations were made on the conditions favour- 

 able for the growth of reef structures by Chamisso and Esch- 

 holz, who accompanied Kotzebue's voyage of exploration 

 (1814-18) in the southern seas. Adalbert von Chamisso, 

 during a prolonged sojourn on an atoll of the Radack group, 

 took accurate measurements, upon the basis of which he after- 

 wards sub-divided coral reefs into three classes, coastal reefs, 

 inland groups, and atolls. Atolls were described as circular or 

 ring islands, rising like table mountains from the ocean depths 

 and only showing a narrow edge above the water. Chamisso 

 distinguished very emphatically the higher side of a reef 

 directed towards the prevailing wind from the lower protected 

 side, which is frequently interrupted, and through which a 

 channel leads into the central lagoon of the island. 



He doubted whether the calcareous rock-material of the reef 



