1/2 Transactions of the [Sess. 



attachment is only a narrow neck that stretches across near where the 

 present Straits of Dover exist. Across this narrow isthmus came 

 another migration of plants and animals to invade Britain, and they 

 gradually spread westwards and northwards to habilitate and occupy 

 the vast tracts of loAvland country that had recently risen from the 

 sea, and which were only partially supplied with vegetable and animal 

 life from the remains of the previous migration that had taken refuge 

 on the hills at the time of the great submersion of the land just re- 

 ferred to. Some time elapses,- — the country that was submerged has 

 recovered from the effects of the sea, — and the hills and valleys are 

 clad with trees, and from a waste there has risen a paradise, when 

 once more there are violent convulsions of the earth — some upheavals, 

 but many subsidences — and the connecting isthmus with the Con- 

 tinent disappears beneath the waves. Britain and Ireland, with the 

 adjoining elevations, once more become islands, and when at last 

 Mother Earth settles down into quietude, the present levels and 

 contour have been attained by the British Isles. Some have sup- 

 posed this convulsion of nature to be the same as the Deluge, but we 

 confess we cannot throw any light upon the subject, so leave it to 

 our theologians, who will find it a difficult point to settle. In dis- 

 cussing the subject before us, we have tried to describe what are the 

 probable changes that have taken place in the relations of sea and 

 land in Western Europe since the last ice age, but we would advise 

 every one to avoid accepting them as definite conclusions until they 

 have verified the evidence for themselves. We need not try to con- 

 tinue this stretch of thought further, as it would be hopeless. For 

 though it may be profitable and instructive to look back upon the 

 past, — whether it be as regards the physical history and changes of a 

 country, or the introduction of its flora and fauna, — we cannot grope 

 into the darkness of the future as we have been doing into the dim- 

 ness of the bygone ages, so must leave it alone. 



XIII.— ANIMAL AND VEGETABLE SYMBIOSIS OR 



GONSOBTISM. 



By Mr JOHN RATTRAY, M.A., B.Sc, F.B.S., 

 Scottish Marine Station, Granton. 



(Read March 27, 1884.) 



Although the highest animals are readily distinguishable from the 

 highest plants, the two kingdoms approximate so closely in their 

 most lowly organised members, that no sharp line of demarcation 

 can be definitely laid down between the two groujos of organisms. 



