30 Origin of the British Flora. 
over six feet high. A few Rock Doves bred near the 
place, and he concluded that an acorn had been brought by 
one of these birds, but where from? Unless it had been 
picked up on the sea-shore, it must have been carried a 
long way indeed. It could hardly have been brought by 
man, as the place was very remote, as well as difficult of 
access. Rooks occasionally cross the Pentland Firth, 
The distance of the north of Hoy from the nearest point 
where Oaks grow is fully as great as is the distance across 
the Strait of Dover; it is probably more than twice as 
great as was the gap between England and France at the 
period when the Oak was re-introduced after the Glacial 
Epoch. Not only have the cliffs of Dover and of Calais 
steadily receded through the inroads of the sea, but when 
the ‘submerged forests’ flourished both the English and 
the French Coasts seem to have been bordered by a wide 
belt of flat land covered with Oaks, the stumps of which are 
now found rooted in the ancient soil as much as forty feet 
below the present sea-level. 
The transportation of large edible seeds for such long 
distances uninjured is probably of exceptional occurrence, 
and is more probably due to rare accidents than to special 
adaptation. Some years ago I found, for instance, in an 
old chalk-pit the remains of a wood-pigeon which had met 
with some accident. Its crop was full of broad-beans, all 
of which were growing well, though under ordinary circum- 
stances they would have been digested and destroyed. 
As fully half at least of the birds that are hatched must 
die by various accidents before the following season, it is 
evident that this dispersal of the contents of their crops 
must be of daily occurrence, A pigeon would easily cross 
the Strait of Dover in half-an-hour, and in the days when 
raptorial birds and wild cats were plentiful, many must 
have been struck down with their last meal undigested. 
