1883-84-] Edinburgh Naturalists Field Club. 167 



from competition with other forms of plant life that choked off, in 

 most instances, the stragglers that dropped out of the ranks at inland 

 situations at lower levels than the arctic-alpine zone. The plants of 

 the alpine, sub-alpine, lowland, and littoral zones all came in succes- 

 sion to take possession of their new home. 



It is not for us to consider at present whether this, the " first 

 post-glacial period of elevation," was for a long or a short time ; hut 

 there is good evidence that, from some cause or other, it was succeeded 

 by a period of great depression, when Britain and Ireland, with their 

 adjoining islands, became insular. This may be gleaned from an 

 examination of the distribution of the reptilian fauna, and on th,at 

 account we refer to the subject here. The arctic-alpine flora, or that 

 portion of it which had taken possession of the Irish hills, would, 

 throu2;h the submersion of the land, be brought much nearer the sea 

 level, and would have to compete for existence under the disadvan- 

 tages of an unsuitable climate with the remains of the alpine, snb- 

 alpine, and lowland vegetation that had found, as stray plants, a home 

 upon the higher ground. These might possibly be poor starved plants 

 that had struggled hard for existence, but luider their changed con- 

 ditions they would gain strength every day, soon grow vigorous, and 

 become strong competitors with the arctic-alpines, many of which 

 would be killed out. This period of depression, Avhich we may call 

 the " first post-glacial land depression," was succeeded by another up- 

 heaval, but not to the same elevations as those attained by the land 

 during the first post-glacial period of elevation. There appears, how- 

 ever, to have been once more a land attachment between Britain and 

 the European continent, and a further influx of flora and fauna ; but 

 probably some of the islands off the west of Scotland were insular at 

 this time, as the upheaval had not been sufficient to give them a land 

 attachment to the mainland. This " second post-glacial period of 

 elevation " was succeeded by a depression of the land to about present 

 levels, by which Britain became insular, and was separated from 

 Ireland and those other islands which had become part of the main- 

 land during the period of elevation. 



Our " raised beaches " and " shell deposits " give us a good index 

 as to the depressions to which our country has been subjected ; and 

 the beds of peat and the remains of sunken submarine forests that 

 extend seawards roimd our coasts, and also from the shores of the 

 European continent, are clear indications that at one time the land 

 was more elevated than at present, and that as the trees composing 

 those forests grew on dry land, there has been a depression of the 

 land by which the forests have been si;bmerged beneath the ocean. 

 The shallowness of the sea that intervenes between Britain and the 

 Continent,-"- and again between Britain and Ireland and the adjoining 



^ See " Depths of the German Ocean," — ' Climate and Time,' by Dr James 

 Croll, p. 479. 



VOL. I. M 



