[63] It would seem, when viewed on a broad scale, as if particular districts throughout the world had been made as it were the special fields for the exercise of the creative force,--or that, _generic areas of radiation_ were part of the elementary design. Thus, Professor E. Forbes records his belief that most, if not indeed _all_, of the terrestrial animals and plants now inhabiting Britain are members of specific centres beyond bounds,--they having migrated to it over a continuous land, before, during, or after the glacial epoch. Hence, since the greater number of them are supposed to have come from the central Germanic plains, we may assume that those plains were one of the primary areas of diffusion for a large mass of created beings. There is good cause for suspecting that the Pyrenean region may have been another; and certainly all evidence would tend to prove that this vast Atlantic province was, also, well stocked with aboriginal forms. [64] Assuming the _Helix Lowei_ and _Bowdichiana_ to be gigantic phases of the _H. Portosanctana_ and _punctulata_, respectively; four only, namely _H. fluctuosa_ and _lapicida_, _Achatina Eulina_, and _Cyclostoma lucidum_ (the first three of which are extinct throughout the entire group), seem to have altogether disappeared. Nevertheless, the gradual dying-out, as it were, of species, both here and in Madeira proper, is singularly evident. Thus, in the latter, the Canical beds show the _H. tiarella_ to have been once most abundant (it literally teems in those calcareous formations). Yet so rare is it in a recent state, that, until the summer of 1855, when it was detected by myself and the Rev. R. T. Lowe in two remote spots along the perpendicular cliffs of the northern coast, it was supposed to have been lost for ages. And the same may be said of its counterpart, the _H. coronata_, in Porto Santo,--which, likewise, swarms in every fossil-bed of that island; but which was, also, until I met with it, on the 15th of December 1848, adhering to slabs of stone at a considerable depth beneath the ground, on the extreme eastern peak (opposite to the Ilheo de Cima), imagined to have long passed away. And so, reasoning from analogy, I think it far from improbable that the third representative of this little geographical assemblage,--the _H. coronula_ of the Bugio (which has hitherto only occurred in the mud deposits on the summit of that rock),--may be still alive, though perhaps in very small numbers, on some of the inaccessible ridges of those dangerous heights. [65] Origin of the Fauna and Flora of the British Isles (in Mem. of the Geol. Survey of Great Britain, vol. i. p. 336, A.D. 1846). [66] "My own belief," says Professor Forbes, "is, that the great belt of gulf-weed, ranging between the 15th and 45th degrees of north latitude, and constant in its place, marks the position of the coast-line of that ancient land."