338 Professor Edward Forbes on the 



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 crea- 

 tures which do not strictly belong to that province, but are 

 identical with similar isolated assemblages on the west coast 

 of Scotland. In the west of Ireland 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 continuation of 

 whose range we must cross the Atlantic to Spain. In such 

 phenomena the Lecturer sees evidences of conformations of 

 land, of outlines of coast and connections of land under dif- 

 ferent climatal conditions than at present prevail within our 

 area, for an explanation 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 dredging researches about to be published go to shew 

 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 difi^using themselves northwards more 

 rapidly than the northern do southwards. 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. "We must attribute it to the influence of 

 warm currents flowing northwards, originating probably in 

 extensions 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, over- 

 lain 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., that 

 the littoral and laminarian forms are peculiarly arctic, whilst 

 the deeper species are boreal or Celtic, may be explained 

 also by the influence of warm currents flowing northwards 

 and diffusing the germs of species of more southern regions 

 in the coralline and deep- sea- coral zones ; for in the arctic 



