244 transactions—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
the Germanic flora spread across the intervening plain, and as the 
temperature grew milder pushed the Alpine plants to the few summits 
where they are now found to exist. 
^ Since the time of Forbes, however, as you are well aware, the 
opinions of geologists have undergone a considerable change as to 
the exact physiographical conditions which prevailed in our country 
during the glacial period. The scratchings and groovings found upon 
the surface rocks of our country are no longer regarded as indicating 
the presence of icebergs in a sea beneath which Great Britain lay 
buried, with only a few of the higher mountain summits rising here 
and there as islands in this Arctic ocean. It is now generally believed 
Aat the groovings and scratchings, along with the accompanying 
boulder clay, are the results of land ice rather than of icebergs, and 
that during the period when they were formed the land was swathed 
in a great ice sheet, similar to that which covers Greenland at the 
present day, it being denied by some that we have any reliable 
evidence of a great submergence during the glacial period, while 
others maintain that such evidence which does exist clearly points in 
the other direction, namely in favour of a submergence of the land. 
We cannot here enter into a detailed examination of the geological 
evidence for and against the occurrence of a great submergence. 
The question is one beset with many difficulties, as the evidence is of 
such a scanty and fragmentary nature that it is often difficult to say 
which way It tells. The principal evidence in favour of such a sub¬ 
mergence is, of course, that derived from the presence of high-level 
shell beds, such as those alleged to have been found at Chapelhall, 
near Airdrie, at an elevation of 510 feet; the well-known Clava 
section, at an elevation of 500 feet; and other similar high-level 
shell beds in England, Wales, and Ireland. With regard to the 
evidence in support of a great submergence supposed to be derived 
from the occurrence of these maritime plants at high altitudes, it will 
be remembered that Dr. Buchanan White in his presidential address 
to the East of Scotland Naturalists’ Union, in 1884, not only referred 
to the geological evidence as all against a great submergence of the 
land, but also cast considerable doubt upon the value of these mari¬ 
time plants as evidence of such a submergence, his own view being 
that these plants grow upon the mountains for the same reason as 
they grow upon the seashores, simply because they have more 
room to grow there. He considered that these maritime plants, 
with the Alpines, once covered all the lower ground, from which they 
have been exterminated in the struggle for existence. 
If, then, it cannot be shown that this great submergence ever 
took place, it remains for us to fix some other period during the ice 
age at which the migration of these Alpine plants may have occurred. 
