, since
the whole of the Bristol Channel to beyond Lundy Island is under
twenty-five fathoms deep. In the east of England we have a similar
forest-bed at Cromer in Norfolk; and in the north of Holland an old land
surface has been found fifty-six feet below high-water mark.

_Buried River Channels._--Still more remarkable are the buried river
channels which have been traced on many parts of our coasts. In order to
facilitate the study of the glacial deposits of Scotland, Dr. James Croll
obtained the details of about 250 bores put down in all parts of the mining
districts of Scotland for the purpose of discovering minerals.[80] These
revealed the interesting fact that there are ancient valleys and river
channels at depths of from 100 to 260 feet below the present sea-level.
These old rivers sometimes run in quite different directions from the
present lines of drainage, connecting what are now distinct valleys; and
they are so completely filled up and hidden by boulder clay, drift, and
sands, that there is no indication of their presence on the surface, which
often consists of mounds or low hills more than 100 feet high. One of these
old valleys connects the Clyde near Dumbarton with the Forth at
Grangemouth, and appears to have contained two streams flowing in opposite
directions from a watershed about midway at Kilsith. At {337} Grangemouth
the old channel is 260 feet below the sea-level. The watershed at Kilsith
is now 160 feet above the sea, the old valley bottom being 120 feet deep or
forty feet above the sea. In some places the old valley was a ravine with
precipitous rocky walls, which have been found in mining excavations. Sir
A. Geikie, who has himself discovered many similar buried valleys, is of
opinion that "they unquestionably belong to the period of the boulder
clay."

We have here a clear proof that, when these rivers were formed, the land
must have stood in relation to the sea _at least_ 260 feet higher than it
does now, and probably much more; and this is sufficient to join England to
the continent. Supporting this evidence, we have freshwater or littoral
shells found at great depths off our coasts. Mr. Godwin Austen records the
dredging up of a freshwater shell (_Unio pictorum_) off the mouth of the
English Channel between the fifty fathom and 100 fathom lines, while in the
same locality gravel banks with littoral shells now lie under sixty or
seventy fathoms water.[81] More recently Mr. Gwyn Jeffreys has