DEPOSITS OF SCOTLAND. 395 
The Boreal shells of Banffshire (which occur at Gamrie in 
a finely stratified sand, two hundred and thirty feet over the 
sea, and at Castleton King-Edward in a similar deposit of very 
considerable elevation, and at least six miles inland), lie deep, 
—though exposed laterally in sections—in the Pleistocene 
deposit. At Castleton I found the shells within a few feet of 
the underlying Grauwacke rock, and an immense deposit of 
beds of sand and clay, and over all a thick bed of partially 
consolidated ferruginous gravel lying above them. At Gamrie, 
though, from the great slope of the ground, the fact is less cer- 
tain, they also seem to lie low; and further, both from their 
littoral aspect, and the circumstance that we find no trace of a 
littoral terrace where they occur, I cannot avoid the conclusion 
that they mark the line where a shore of the country existed 
for a time, when the country was in a state of subsidence, and 
ere yet the higher lying boulder clay was formed. The only 
peculiarity of the shells themselves, viewed in the group, is 
their intensely boreal character. The sole species of Astarte 
which I have yet found at either Gamrie or Castleton King- 
Edward,— and I have now visited these deposits five several 
times,— is the Greenland shell, Astarte Arctica ; Natica clausa, 
—a shell of Spitzbergen and the North Cape,— is the pre- 
vailing Natica; and the most abundant shell, of at least the 
Gamrie deposit, is a bivalve not yet found living in our seas, 
but common ten degrees further to the north, Zelina proxima., 
Even the great size to which the latter shell attained in this 
locality is not without its bearing on the question. “The few 
specimens which have been dredged [dead] in Britain,” says 
the late Professor Forbes, in his admirable history of the Brit- 
ish Mollusca, “are much smaller than the exotic ones, none 
which we have seen exceeding three-quarters of an inch in 
length, and about half an inch in breadth.” The molluse is one 
of those which attain to their fullest development amid the 
