OP SCOTLAND.

377

The boreal shells of Banffshire (which occur at Gamrie ina finely stratified sand, two hundred and thirty feet over thesea, and at Castleton King-Edward in a similar deposit ofvery considerable elevation, and at least six miles inland), liedeep,—though exposed laterally in sections,—in the Pleisto­ cene deposit. At Castleton I found the shells within a fewfeet of the underlying Grauwacke rock, and an immense de-posit of beds of sand and clay, and over all a thick bed ofpartially consolidated ferruginous gravel lying above them.At Gamrie, though, from the great slope of the ground, thefact is less certain, they also seem to lie low; and further, bothfrom their littoral aspect, and the circumstance that we findno trace of a littoral terrace where they occur, I cannot avoidthe conclusion that they mark the line where a shore of thecountry existed for a time, when the country was in a stateof subsidence, and ere yet the higher lying boulder clay wasformed. The only peculiarity of the shells themselves, view-ed in the group, is their intensely boreal character. The solespecies of Astarte which I have yet found at either Gamrieor Castleton King-Edward,—and I have now visited thesedeposits five several times,—is the Greenland shell, AstarteArctica; Natica clausa ,—a shell of Spitzbergen and the North Cape, —is the prevailing Natica ; and the most abundant shell,of at least the Gamrie deposit, is a bivalve not yet found liv-ing in our seas, but common ten degrees further to the north,Tettina proximo. Even the great size to which the lattershell attained in this locality is not without its bearing onthe question. “ The few specimens which have been dredged[dead] in Britain, ” says the late Professor Edward Forbes , inhis admirable history of the British Mollusca , “are muchsmaller than the exotic ones, none which we have seen ex-ceeding three-quarters of an inch in length, and about halfan inch in breadth.” The mollusc is one of those which at-tain to their fullest development amid the frosts and snows