464 On the Post-Tertiary Beds [ Oct., 
Taking the older arctic shell-clays generally, Sars has described 
fifty-nine species of mollusca from the Norwegian beds, and of 
these fifty-nine species forty-eight have been collected in Scotland 
by Mr. Robertson and the writer. Sars has collected his speci- 
mens from Trondhjem to Avemark ; we have collected ours from 
Caithness to Paisley, and are yet only deficient in eleven species, 
all of which may possibly occur in connection with those already 
found, since they have at the present day the same habitat in the 
Northern seas. 
The great divisions under which the glacial fossils of Scotland 
may be classified render this comparison still more striking. The 
first class includes mollusca, unknown in the British seas, but living 
in high northern latitudes, such as Astarte borealis, Pecten Groen- 
landicus, Tellina calcarea, Velutina undata. The second class 
comprises northern forms of species yet existing in British seas. 
Trophon clathratus, e.g. attains a large size, while Lacuna divaricata 
occurs in a variety, which Torell states can be abundantly collected 
on the coast of Iceland. The third class includes species compa- 
ratively rare in British waters, but very abundant in the shell-clays. 
Panopcea Norvegica, e.g., now only found in deep water on the 
Dogger Bank, is far from rare as a glacial fossil. The fourth class 
includes those species which, while found both living and fossil in thei 
ordinary forms, have yet a high range, no shell being found fossil in 
the older glacial clays which does not also possess an arctic habitat. 
Associating together these facts, (1) the precise agreement 
between the characteristic shells at special localities ; (2) the actual 
occurrence in Scotch beds of a large proportion of the most arctic 
species of the Norwegian clays; (3) the exhaustive classification 
which may be made of the glacial fossils of Scotland, showing even 
the most delicate arctic variation of existing species; we have a 
close correspondence of conditions now only prevalent in very high 
latitudes, common to Scotland and Norway during the glacial 
epoch. 
4 The elevation of the older shell-clays of Norway extends from 
10 feet to 450 feet, or 500 feet above the sea-level. Balani have 
been found attached to the rock in Avemark at a height of 450 feet. 
The highest shell-bed found in Scotland is 526 feet, near Airdrie, 
and the beds extend to this height, as in Norway, from points not far 
above sea-level. The correspondence upon several points of detail 
connected with this elevation of the earth’s crust, is curious. Within 
a radius of a few miles near Glasgow, shell-beds of the same glacial 
character crop out at varying heights, from half-tide mark, in the 
estuary of Clyde, to 10 feet, 40 feet, 150 feet, 526 feet. In the 
Christiania fjord the same phenomena appear. A clay bed may 
be found, e. g.,50 feet above the sea, and within a few miles another, 
belonging to the same age in its fossil contents, at 240 feet. 
