396 THE FOSSILIFEROUS 
frosts and snows of the higher latitudes; and it is a curious 
fact, that in the Gamrie and Castleton deposits we find it of a 
considerably greater size than anywhere else in Scotland. My 
largest specimens from the Clyde beds hardly exceed an inch 
in length; whereas my largest Gamrie specimens are nearly 
two inches long, and their breadth very considerably exceeds 
the length given as British by Professor Forbes. 
Most of the boulder clays,—especially the higher lying 
deposits— I regard as more modern than these Banffshire 
beds. They mark a period when the land sat low in the 
water, and existed as but a group of wintry islands. ‘To the 
south of the Grampians, their organisms are but few; they 
have yielded at wide intervals horns of the rein-deer, and tusks 
of the northern elephant; but, save in an insulated patch in 
Wigtonshire, no shells. The boulder clay in Caithness is, on 
the other hand, rich in shells. They excited the attention of a 
mineral surveyor, who flourished about the beginning of the 
present century,—old John Busby,—more than fifty years 
ago; they also attracted the notice of the late Sir John Sin- 
clair; and in one of my Caithness journeys, I was told by my 
friend Mr. Dick, that one of the hills on which they occur has 
borne from a still more early period the name of “ Buckie’s 
Hill;” but to Mr. Dick himself, and to Mr. Cleghorn of Wick, 
has the working out of the deposit been mainly left. And so 
effectively has it been done, that Mr. Dick, as he informs me, 
has not for a considerable time past succeeded in finding in it a 
single new shell. The prevailing molluses of the deposit are 
Cyprina, Islandica, and Turritella communis, especially the 
former ; the prevailing Astarte, though the Arctica also occurs, 
is Astarte elliptica; the prevailing Tellina, Zellina Solidula. 
Tellina proxima is of smaller size than in the Gamrie beds; 
and Natica clausa Jess common. Still the deposit is very 
decidedly a boreal one in its shells, and in its mechanical phe- 
