238 The Irish Natiii'alist, [Sept., 



Now. here comes the possible difference of view between the geologist 

 and the zoologist. The latter, argning from his most natural study, 

 distribution at the present day or in very recent deposits, concludes that 

 a species arose near its position of maximum abundance. For some 

 reason or other, moreover, the fact that the British Isles are islands now- 

 a-days, has made everyone ready to speak of the migration of forms into 

 those islands. The origin of European species within the area of the 

 British Isles, and their migration outwards when local conditions became 

 less favourable for their multiplication, are possibilities that seem too 

 often disregarded. Yet the geologist must see in the western border- 

 lands of modern Europe a diminished continent from which land- 

 animals must have again and again moved eastward. The south-eastern 

 sea, at one time a series of gulfs, at another a swelling ocean, has been 

 a phenomenon of such frequent recurrence and of such amazing geologi- 

 cal antiquity, that even at the present day one may be chary as to landed 

 investments in the East. Species of Carboniferous labyrinthodonts 

 may have originated in Kilkenny ; mammals may have arisen at Bristol 

 independently of their South African relations ; the land-fauna of 

 Jurassic and of Cretaceous times must have been thrown far west- 

 ward by the spread of the eastern ocean, and must have gone on 

 flourishing in the hills of Donegal and Connemara. The mammals of 

 Eocene times are best known from French deposits; but they must have 

 found a broader ground for exercise in the dry land that stretched 

 continously where our western isles at present stand. In middle Miocene 

 times, during the Helvetian age. there must have been a veritable 

 hviddling together of the land-fauna towards Great Britain ; the crowding 

 would lead to fiercer competition, the keener processes of selection 

 would lead to the origin of species. Hence geologists may fairly be 

 unwilling to look on our isles as barren lands waiting to be peopled in 

 Pliocene or later times. Far rather has the breaking up of a broad land- 

 area along the present continental edge sent our land-fauna to the new 

 steppes that opened eastward, leaving us a mere diminished remnant to 

 struggle with the glacial epoch. 



The rich terrestrial population here suggested would leave, however, 

 scarcely any traces in our own Cainozoic strata. It is only in fortunate 

 pockets, as it were, in the river-swept lands of Europe that any number 

 of mammalian remains have been preserved. To this day, the little 

 digging on the farm of Pikermi, and the local deposit of Mont Leberon, 

 are our chief storehouses for the land-fauna of the lower Pliocene in 

 Europe. The richness of these deposits, however, points to an abundance 

 of individuals across the continent. In our own area, the enormous 

 denudation that accompanied the glacial epoch, whether we regard 

 swollen rivers, or marine currents, or even moving ice-sheets, as the 

 agent, would effectually sweep away the larger part of our previous 

 land-deposits, some of which may have dated back to Eocene times. 

 How much is now buried under " drift " is quite uncertain ; but it is 

 improbable that any recognisable deposit can remain. It required half 

 the plateau-eruptions of Antrim to preserve the only Cainozoic land- 



