P. MACNAIR ON THE ALPINE PLANTS OF PERTHSHIRE. 245 
It is generally supposed by those who deny that these plants reached 
our country during a great submergence of the land, that the most 
likely period at which this could have taken place would have been 
towards the close of the glacial period, when the last traces of the 
local glaciers had disappeared, or at least when they had retired to 
the higher reaches of the mountains. From evidence into which we 
cannot now enter, it is supposed that towards the close of the ice age 
the British Isles underwent a slow upheaval to a height probably 
corresponding with the 8o-fathom line, the consequence being that 
the present bed of the North Sea was elevated into land through 
which flowed the Rhine, with the Thames, Ouse, Tay, and other 
British rivers now entering the North Sea as its tributaries. At this 
time the English Channel, St. George’s Channel, and the Irish Sea 
were also land, forming a group of low-lying grounds uniting Britain 
and Ireland to the Continent, so that the immigration of the Scan¬ 
dinavian flora took place step by step across the plains from these 
boreal centres of dispersion until they covered the whole of the 
British Isles. Professor James Geikie, in “ Prehistoric Europe,” has 
gone the length of contending that an elevation of the present sea 
bottom to the 500-fathom line must have taken place, and his prin¬ 
cipal argument in favour of such an extensive upheaval is that derived 
from the presence of representatives of the Scandinavian flora in the 
Faroe Islands, which he maintains could not have reached these 
islands without a land connection with their centres of dispersal. 
Mr. A. J. Jukes Browne, however, in his “ Building of the British 
Isles,” after citing Mr. A. R. Wallace’s views upon island floras, says : 
—“ The Scandinavian character of the Faroe flora can be explained 
by other means than the great elevation which would have been 
required to unite it to Scotland, and we may therefore dismiss Pro¬ 
fessor Geikie’s views of the geography of this period as quite unwar¬ 
ranted by the facts which are known to us.” 
It might here be noted that within the last two years the great 
submergence theory has again been brought before us in a prominent 
manner, and that principally owing to the researches of Mr. John 
Smith, of Kilwinning, who has shown that in Ayrshire we have 
evidence of a submergence to a height of over a thousand feet, a high- 
level shell bed being described as occurring at Dippal, in Ayrshire, at 
an elevation of 1061 feet, and quite evidently in situ, and with other 
beds covering an area of ten square miles. This author has also 
resuscitated the evidence supposed to be derived from the presence 
of maritime plants at high levels as favourable to the view of a great 
submergence, though, as we have already stated. Dr. Buchanan 
White has shown us that this evidence is exceedingly unreliable. 
Without entering into details, it seems to us that so far as we are 
