Mr. E. W. H. Holdsworth on the Distribution of Corals. 147 



Milne-Edwards. The specimens, however, are so young and imper- 

 fect that it is difficult to determine their specific characters. 



If we now turn to the eastern side of Great Britain, and inquire 

 whence come the waters of the German Ocean, we find them to be 

 mainly of Polar origin, brought from the far north by the great 

 surface-current which washes all the Norwegian and our own eastern 

 coasts. To this must be added the comparatively fresh water which 

 pours through the Sound, loaded with all the drainage of the Baltic. 

 How does this cold and impure water affect the production of corals ? 

 Its influence is not less marked than that of the warmer western 

 current. Through the entire length of the North Sea, from the 

 north-eastern point of Scotland to near the Isle of Wight, I have 

 been unable to ascertain that a single specimen of coral has ever 

 been taken. That line of coast is also very deficient in Actinice ; 

 and of the few that are found there, most are of the commonest spe- 

 cies. This cold water from the north, however, also skirts the western 

 coast of Scotland and Ireland ; but it is only as a narrow superficial 

 current ; and when corals are found in its neighbourhood, they are 

 only in the deep water of the great Atlantic stream, which, still re- 

 taining some of its excess of saline matter, sinks deeper and deeper 

 as it meets the fresher and lighter, although colder, water from the 

 north. Thus, as has been observed, all the northern corals are found 

 in deep water, even the same species which on the Devonshire coast 

 is abundant at low-water mark. The late Edward Forbes, in his 

 ' Natural History of the European Seas,' remarks that the charac- 

 teristic fauna of the "Arctic province" is only to be observed in the 

 littoral regions, and the animals from deep water are all of them 

 southern forms. . 



What has been pointed out as to the causes of the particular dis- 

 tribution of the British corals, namely, the effect of warm and cold 

 currents, equally applies to the formation of coral-reefs within the 

 Tropics. A comparison of Maury's Chart of the " Sea-drift" with 

 Darwin's Map of the Distribution of Coral-reefs would lead one 

 to suppose they had been prepared by the same hand. I will men- 

 tion two remarkable cases as illustrations. A well-known barrier- 

 reef extends some hundreds of miles along the north-east coast of 

 Australia; its southern limit is near Moreton Bay ; and a reference to 

 Maury's Chart shows this to be the precise point at which a cold cur- 

 rent from the South Pole meets the warm equatorial current from the 

 east. Again, it appears somewhat remarkable that along the whole 

 western coast of North and South America no vestige of coral has 

 been found. Mr. H. Cuming informs me that he has dredged in 

 vain for specimens of these characteristic tropical productions in the 

 Bay of Panama and at the Galapagos ; but the chart shows that 

 cold currents from the north and south sweep the whole western 

 coasts of America, meeting at the Equator, and then turning away 

 into the Pacific, where, under a vertical sun, the water soon becomes 

 warm enough for the growth of the various coral-reefs scattered 

 about in that ocean. Fresh water and sediment of any kind being 

 present act as fatal barriers to the growth of coral ; and to these 



