DISTKIBUTION OS COEALS. 249 



growth, and that but little, if any, transference of species from one 

 side to the other was effected.* The principal reefs of the sub- 

 torrid zone, other than the South Pacific, are those of the Bermudas 

 and the Sandwich Islands, both of which are characterised by a 

 comparative paucity of specific forms. Most of the species occiirring 

 among the former (Isophyllia, Diploria, Oculina, Siderastrea, Pori- 

 tes) are West Indian types ; in the Sandwich Islands the predomi- 

 nating forms are Porites and Pocillopora, there being a marked 

 deficiency in the representatives of the Astraea and Fungia tribes, 

 and a complete absence of Madrepora. The point most distant 

 from the Equator about which reef -structures have been noted ap- 

 pears to be Quelpaert's Island, situated south of Corea on the 

 thirty-fourth parallel of north latitude. 



In comparing the past with the present distribution of coral 

 reefs, we are at once confronted with the not very surprising, al- 

 though all-important, fact that the areas of such distribution in no 

 way correspond with those distinctive of the modern seas. The 

 extension of reefs northward to points far beyond any now occu- 

 pied by such structures is practically proof positive of the existence 

 of thermal conditions very different from those which obtain at the 

 present day, and of a much more equable climate, with a more 

 elevated temperature, than is now found in the higher latitudes of 

 the earth's surface. Palaeozoic reef-building corals have been found 

 in Eurasia (Scandinavia, Russia) far above the sixtieth parallel 

 of latitude, and a number of genera even in Spitzbergen, Nova 

 Zembla, and Barentz Islands; Lithostrotion was obtained by the 

 officers of the British North-Pole Expedition, under command of Sir 

 George Nares, at a point beyond the eighty-first parallel of latitude. 

 The reef-building corals of the Silurian and Devonian periods — 

 Pavosites, Heliolites, Halysites, Syringopora, Cyathophyllum, Acer- 

 vularia, &c. — have left traces of their profuse development in seas 

 as far north as Canada and Scandinavia, but it would perhaps be 

 straining a point to infer from their occurrence there that climatic 

 conditions in any way identical with those existing in the modern 

 coral zones prevailed during those periods in high northern lati- 

 tudes. Our knowledge respecting the habits and affinities of these 

 ancient organisms is still much too limited to permit of a positive 



* All the species descrilsed by Duncan trom the Oligocene deposita of the 

 island of St. Bartholomew are extinct. 

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