This decision as to the relative age of the British South-western fauna has not been arrived at from any geological considerations. The conviction that it must be older than the other sections has been gained solely from a study of the geographical distribution of the species belonging to that fauna. Many of them exhibit what is known as "discontinuous distribution," which zoologists are agreed to regard as a sign of antiquity. Thus _Geomalacus maculosus_, the Kerry Slug, is in the British Islands confined to South-western Ireland (see Fig. 19, p. 300), and on the Continent it is unknown north of North-western Spain. The Millipede, _Polydesmus gallicus_, has a wider range in Ireland, and is also known from France and the Azores. Two Earthworms of the Spanish and Mediterranean region, viz., _Allolobophora veneta_ and _Georgii_, have been discovered in Ireland, but are apparently unknown in England or France; whilst the Weevil, _Otiorrhynchus auropunctatus_, does not occur north of the Auvergne Mountains in France except in Ireland. A very large number of instances might be mentioned of species found in South-western Europe, France, the South-west of England and Ireland. Enough, however, has been said to show the nature of the fauna, and there is, as Forbes has pointed out, a corresponding flora. A great number of the species belonging to the South-western British element seem to have originated in South-western Europe, or at any rate to have spread over our continent from that part. Their home lay therefore probably in a warm, damp climate, and it seems a reasonable inference to suppose that they spread north at a time when the temperature over the British Islands was much higher than what it is now. Any one familiar with our Bristle fern, or Killarney fern, as it is called in Ireland (_Trichomanes radicans_), will readily admit that it must have come to us at such an epoch. It at once suggests some shady waterfall in a tropical forest, and indeed the home of the genus is South America. It is one of those plants which have evidently migrated to us from South-western Europe, a mere remnant of a once luxuriant flora.