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XVII. »I may liere biiefly notice the remarkable absence of the reef 

 » building polypi over certaia vride aieas of the iatevtropical seas , for 

 siastaiice the West coasts of Amciica and of Afiica, niid the islands ia 

 »that iide of the Atlantic falso the coast of Western Australia, onwliich 

 »thera are coraparatively with the Eastern coast of Africa, uo coralline 

 »formations of any consijerable importance) , it would appear the effcc- 

 »tive Creef building) species do not cccui' there, of -which ciiciimstance I 

 »apprehend no explauaiioa can be gi^en, any nioic than why ichas been 

 »ordaiaed that certaia plants, as heaths, should be absent from the New 

 » World, altho' so common ia the old." 



Mr. Darwin will certainly tliink tliat we are monstrously 

 presumptious iu attempting, as we are about doing, to give 

 a //probable explanation," after he has apprehended that none 

 can be given; but n'importe, liere comes the result of our 

 attempt. 



Along and to some considerable extent in longitudinal di- 

 stance from the western coast of Iniertropical (1) America, Aus- 

 tralia and Africa, currents having a low temperate and consequent- 

 ly no sufficiënt food for the polypi &c., run from the extra- 

 tropical seas towards the Equator, thence proceeding and sprea- 

 ding out to the westward. The water driven onwards by the 

 trade winds and warmed by the solar heat is accumulated in 

 the western regions of the oceans, where, fraught with food 

 and material for the use of the coral builders and constructions 

 of their accumulations and thence running ofl', from the Eauator, 

 along the eastern coasts of those continents , these warm waters , 

 enable those coral builders to extend their works proportionably 

 far towards the extropical regions. It may be supposed, that 

 this does not account for the abundance and activity of these 

 werkers in the middle regions of the Pacific, but the supposi- 

 tion must be withdrawn , after the fact is known , that the ther- 

 mo-equatorial westerly winds, which annually extend alterna- 

 tely to the southward and northward as far as the coral for- 

 mations, bring along with them sufficiently warm water and 



(1) By this appellaliou meaniiig tlie rouge of the trade wiuds, or from 

 30» Nurth to 30" Suuth of the Efiuatar. 



