African lion), whose bones are found in the gravels and the caverns
of these isles.

And how long ago were those days of mammoths and reindeer, lions and
hyaenas? We must talk not of days, but of ages; we know nothing of
days or years. As the late lamented Professor Sedgwick has well
said:-

'We allow that the great European oscillation, which ended in the
production of the drift (the boulder clay, or till), was effected
during a time of vast, but unknown length. And if we limit our
inquiries, and ask what was the interval of time between the newest
bed of gravel near Cambridge, and the oldest bed of bogland or silt
in Cambridgeshire and Norfolk, we are utterly at a loss for a
definite answer. The interval of time may have been very great. But
we have no scale on which to measure it.'

Let us suppose, then, the era of 'gravels' past; the valleys which
open into the fen sawn out by rivers to about their present depth.
What was the special cause of the fen itself? why did not the great
lowland become a fertile 'carse' of firm alluvial soil, like that of
Stirling?

One reason is, that the carse of Stirling has been upheaved some
twenty feet, and thereby more or less drained, since the time of the
Romans. A fact patent and provable from Cramond (the old Roman port
of Alaterna) up to Blair Drummond above Stirling, where whales'
skeletons, and bone tools by them, have been found in loam and peat,
twenty feet above high-water mark. The alluvium of the fens, on the
other hand, has very probably suffered a slight depression.