234 Royal Institution. 



searches, when scientifically conducted, have confirmed this classi- 

 fication of provinces of depth. When we have an apparent exception, 

 as in the case of the suhmarine ravine off the jMull of Galloway, 

 dredged hy Captain Beechey and recorded hy Mr. Thompson, in 

 which, though it is 150 fathoms deep, the fauna is that of the coral- 

 line zone, we must seek for an explanation of the anomaly by in- 

 quiring into the geological history of the area in question. In this 

 particular instance there is every reason to believe that the ravine 

 mentioned is of a very late date compared vyith the epoch of diffusion 

 of the British Fauna. 



When we trace the horizontal distribution of creatures in the British 

 seas, we find that though our area must be mainly or almost entirely 

 referred to one of the great European marine provinces, that to which 

 the lecturer has given the name of Celtic, yet there are subdivisions 

 within itself marked out by the presence or absence of peculiar species. 

 The marine fauna and flora of the Channel Isles present certain dif- 

 ferences, not numerous, but not the less important, from that of the 

 south-western shores of England, which in its turn differs from that 

 of the Irish Sea, and it again from that of the Hebrides. The Cor- 

 nish and Devon sea fauna and that of the Hebrides are marked by 

 redundancies of species ; that of the eastern coasts of England, on the 

 contrary, by deficiencies. Along the whole of our western coasts, 

 whether of Great Britain or Ireland, we find certain creatures pre- 

 vailing, not present on our eastern shores. In the depths off the 

 south coast of Ireland we find an assemblage of creatures which do 

 not strictly belong to that province, but are identical with similar iso- 

 lated assemblages on the west coast of Scotland. In the west of Ire- 

 land we find a district of shore distinguished from all other parts of 

 our coast by the presence of a peculiar sea-urchin, to find the con- 

 tinuation of whose range we must cross the Atlantic to Spain. In 

 such phsenomena the lecturer sees endences of conformations of laud, 

 of outhnes of coast, and connections of land with land under different 

 climatal conditions than at present prevail within our area, for an ex- 

 planation of which we must go back into the history of the geological 

 past. If we do so, we can discover reasons for these anomalies, but 

 not otherwise. 



The dredgmg researches about to be pubhshed go to show that 

 among our sublittoral animals the northern element prevails over 

 the southern, — a fact indicated by the number of peculiar northern 

 species ; at the same time the southern forms appear to be diffusing 

 themselves northwards more rapidly than the northern do south- 

 wards. This diffusion is mainly maintained along our western shores, 

 and appears to be in action, not only in the British seas, but also 

 along the shores of Norway. AVe must attribute it to the influence 

 of warm currents flowing northwards, originating probably in exten- 

 sions of the Gulf-stream. The body of colder water in the depths of 

 our seas preserves the original inhabitants of this area, remnants of 

 the fauna of the glacial epoch, overlain and surrounded by a fauna 

 of later migration, and adapted to a higher temperature. A curious 

 fact respecting the marine creatures of the Arctic seas of Europe, viz. 



