ORIGIN OF LOCAL FLORAS. 
37 
uplifted into lofty peaks and mountain cliains of unusual 
grandeur and magnitude. It is not unreasonable to tliink 
tkat even the tops of the mountains of Wales and Scotland, 
which, ever since their upheaval, have been disintegrating and 
wearing down, were at this remote era Avhitened with the 
snows of a perpetual winter, especially as the neighbouring* 
valleys abound in evidences of former glacial action. 
Those sub-arctic plants which formerly grew on the cold low 
lands in the neighbourhood of the glacial sea now became 
mountain plants ; and therefore, notwithstanding the change 
of climate, still maintained their footing in the old spots, in 
consequence of the diminished temperature resulting* from 
their elevation. It was over the great plain thus formed 
from the west of Ireland to Germany that the plants consti- 
tuting the great bulk of our flora appear to have migrated. 
Both plants and animals came across this great Germanic 
plain, and their descendants still continue to constitute the 
great body of the fauna and flora of om* lowlands. The south- 
east of England was also at this time united to France, and 
received from that counti*}^ its French plants, which, for a 
series of ages, were thus enabled to extend themselves from 
France into England, as now from one department of France 
into another. 
The complete separation of Great Britain from Ireland and 
the Continent, is- one of the last changes in the physical geo- 
graphy of the United Kingdom, and comparatively speaking 
a recent event; although it undoubtedly took place many 
thousands of years before the appearance of man in Em*ope. 
Certainly, the ideas of Forbes on the origin of our Arctic 
flora deserve to be regarded now, not as an hypothesis, but as 
a probability, because they repose on geological data which 
are becoming every day better established. This glacial sea 
has everywhere left its traces over the Continent and the 
British Isles. The plains of Prussia, Poland, and Pussia, are 
strewed with loose detritus and colossal crystalline blocks 
which have had their parent bed in the mountains of Scandi- 
navia. England and Ireland show similar phenomena. These 
drift materials known to geologists as diluvial gravel, grey 
heads, and boulders, formerly adduced as afibrding physical 
proof of the Noachian deluge, are now known to have been 
conveyed to their present sites by ancient glacial action. This 
process is now going on in nature. Glaciers are always more 
or less loaded with heaps of gravel and blocks of stone. They 
are never formed except at the edge of ice-covered lands. 
When they come down from the mountains into the warmer 
regions of the valleys, the ice necessarily melts, and the gravel 
and blocks are left lying on the earth^s surface. In the same 
