1S83-S4.] lid'Diburgh Naturalists Field Club. lyi 



to reach Colousay and Oronsay at a later time, suppnsiii.n' tliat they 

 had not arrived in tliose islands diuin,^- the time of a land connection 

 with the mainland, wonld he more tliffionlt to prove to the satisfac- 

 tion of most persons than that a Slnw-worm or a green Lizard could 

 not get over the intervening stretch of ocean. The swimming feats 

 of some animals are remarkable, and perhaps none more so than tlie 

 Eed-Deer, which, though now extinct on many of the islands round 

 our shores, still has left a record of its presence at one time on 

 almost all of them, in its remains. The evidence obtained during a 

 series of excavations in ancient deposits on the islands of Colonsay 

 and Oronsay leads us to believe that, in all probability, n\imbers of 

 the mammalia at one time found there, but now extinct on those 

 islands, originally reached them during a period of land attachment 

 with the mainland. But it would lengthen out our subject too much 

 to enter upon our reasons for that conviction. 



We must now ask you to join with us in briefly reconsidering the 

 probable physical changes that Western Europe has undergone since 

 the close of the last glacial period. In imagination, suppose your- 

 selves standing upon an eminence that enables you to survey at one 

 glance the tract of land — now partly sea — that intervenes between the 

 west of Scotland and the western shores of the Continent, and stretch 

 back in thought into the immense period of time that has elapsed 

 since the last ice age. You will see (after the ice melted from the 

 littoral zone, and retired up the mountain sides, where it remained 

 in immense glaciers) what is now the bed of the German Ocean be- 

 coming dry land, and the ground taken possession of by the arctic- 

 alpine flora, which ever pressed westwards, followed rapidly, as the 

 climate ameliorated, by alpine, sub-alpine, and littoral plants, all in 

 quick succession pressing to the new home they were in search of in 

 the country of the setting sun. As with the plants, so with the 

 animals — all are rushing west to take possession, as soon as the con- 

 ditions exist that enable them to live. The climate gradually be- 

 comes warmer and warmer, each recurring season, until it is like that 

 which now exists in the south of Europe. This continental period 

 has lasted a long time, when there are sudden and violent changes 

 that alter the position of land and sea, causing Britain and Ireland 

 to become insular, some of their outlying elevations becoming islands. 

 This submersion has the effect of drowning out almost the whole of 

 the lowland flora, and kills many of the alpine and arctic-alpine 

 jilants, from a withdrawal of the suitable conditions for life. The 

 fauna has to flee from the plains before the rising waters, and take 

 refuge on the bare mountain sides, Avhere many animals die from want 

 of food. Another long period elapses, and the plant and animal life 

 have got settled down into their new circumstances, the fittest sur- 

 viving ; when an upheaval takes place, and Britain and most of the 

 adjoining islands once more become continental, though the land 



