28 FOUNDERS OF OCEANOGRAPHY 



may have migrated into the south and west of Ireland. 



The fauna of our seas also, like the land flora, presents 

 distinct northern and southern relations. This is clearly 

 seen both amongst the invertebrata, such as the molluscs, 

 and also amongst fishes. In discussing these relations, one 

 of the most interesting points that Forbes demonstrated 

 was the presence of " boreal outliers " or assemblages of 

 northern species occupying the deeper areas of about 80 to 

 100 fathoms that occur here and there on the west coast of 

 Scotland. Such molluscs as Puncturella noachina, Tricho- 

 tropis horealis, Natica groenlandica, Astarte elliptica, Nucula 

 pygmcea, Emarginula crassa, Pecten danicuSy Necera cusjn- 

 data, and the brachiopods Terebratida caput- serpentis and 

 Crania norvegica,^ are characteristic forms in these boreal 

 outliers, and Forbes's view was that they were a part of the 

 original northern fauna which formerly occupied our seas 

 and which had retreated northwards when the climate became 

 more genial subsequent to the glacial epoch, leaving these 

 colonies isolated in the deeper holes (see map, PI. IV, Fig. 2). 



Some of the chief conclusions, to which the facts and 

 arguments stated in his detailed memoir lead, he summarizes 

 as follows : — 



" (1) The fauna and flora, terrestrial and marine, of the 

 British Islands and seas have originated, so far as that area 

 is concerned, since the Miocene epoch. 



" (2) The assemblages of animals and plants composing 

 that fauna and flora did not appear in the area they now 

 inhabit simultaneously but at several distinct points of time. 



" (3) Both the fauna and flora of the British Islands and 

 seas are composed partly of species which appeared in that 

 area before the glacial epoch, partly of such as inhabited it 

 during that epoch, and in great part of those which did not 

 appear there until afterwards. 



" (4) The greater part of the terrestrial animals and flower- 

 ing plants now inhabiting the British Islands arose outside 

 1 1 have given throughout the names as used by Forbes. 



