MAKINE SHELLS OF SCOTCH DRIFT. 
Ill 
clay is at Airdrie, in Lanarkshire, ten miles east of Glasgow, 
524 feet above the level of the sea. At that spot they were 
found imbedded in stratified clays with till above and below 
them. There appears no doubt that the overlying deposit 
was true glacial till, as some boulders of granite were ob¬ 
served in it, which must have come from distances of sixty 
miles at the least. 
The shells above figured are only a few out of a large 
assemblage of living species, which, taken as a whole, bear 
testimony to conditions far more arctic than those now pre¬ 
vailing in the Scottish seas. But a group of marine shells, 
indicating a still greater excess of cold, has been brought to 
light since 1860 by the Rev. Thomas Brown, from glacial 
drift or clay on the borders of the estuaries of the Forth 
and Tay. This clay occurs at Elie, in Fife, and at Errol, in 
Fig. 113. Fig. 114. 
Leda tru7icata. T’ellma calcarea, Chem. {Tellinaproxima^ 
Brown.) 
a. Exterior of left valve. 6. Interior a. Outside of left valve. 6. Interior i 
of same. of same. 
Perthshire; and has already afforded about 35 shells, all of 
living species, and now inhabitants of arctic regions, such as 
Leda truncata^ Tellina proxima (see Figs. 113, 114), Pecteu 
Groenlandicus^ Crenella Icevigata^ Crenella nigra^ and others, 
some of them first brought by Captain Sir E. Parry from 
the coast of Melville Island, latitude 76° IST. These were all 
identified in 1863 by Dr. Torell, who had just returned from 
a survey of the seas around Spitzbergen, where he had col¬ 
lected no less than 150 species of mollusca, living chiefly on 
a bottom of fine mud derived from the moraines of melting 
glaciers which there protrude into the sea. He informed 
me that the fossil fauna of this Scotch glacial deposit exhib¬ 
its not only the species but also the peculiar varieties of 
mollusca now characteristic of very high latitudes. Their 
large size implies that they formerly enjoyed a colder, or, 
what was to them a more genial climate, than that now pre¬ 
vailing in the latitude where the fossils occur. Marine shells 
have also been found in the glacial drift of Caithness and 
Aberdeenshire at heights of 250 feet, and in Banff of 350 
feet, and stratified drift continuous with the above ascends 
to heights of 500 feet. Already 75 species are enumerated 
