1862.] MR. HOLDSWORTH ON THE DISTRIBUTION OF CORALS. 201 
western promontory of England can boast of five out of the eight 
undoubted British species. They consist of two Caryophyllia, one 
Sphenotrochus, Balanophyllia, and Hoplangia. Of these species, 
Guernsey produces two. Caryophyllia smithii, the commonest species 
in the West of England, where it is found close to low-tide mark, 
ranges along the eastern and northern coasts of Ireland and the 
West of Scotland as far as Shetland, gradually increasing its depth 
of water as it proceeds north. It has also been met with on the 
western coast of Ireland; but very little has been done as yet in 
exploring the Atlantic sea-board of that island. Among the Hebrides 
and Orkneys, the fine branching coral Oculina prolifera has on rare 
occasions been met with, but only in deep water. Two species of Ca- 
ryophyllia and the large scarlet Ulocyathus arcticus have been ob- 
tained in 80 or 90 fathoms near Shetland ; the last-mentioned coral 
has also been taken by Sars at a depth of nearly 200 fathoms near the 
North Cape. Three other little corals have been dredged in the 
Moray Frith, and placed by Mr. Gosse in the genus Paracyathus of 
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 Actinie ; 
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 
