244 SUBAQUEOUS DRIFT IN PERTHSHIRE. chap. xm. 



blage of shells implj^ing a coldei' climate than that of the 

 twenty-five foot terrace, or that of the present sea; just as, in 

 the valley of the Somme, the higher-level gravels are sup- 

 posed to belong to a colder period than the lower ones, and 

 still more decidedly than that of the present era (see p. 142). 

 At still greater elevations, older beds containing a still more 

 arctic group of shells have been observed at Airdrie, fourteen 

 miles southeast of Glasgow, 524 feet above the level of the 

 sea. They were imbedded in stratified clays, with the nn- 

 stratified boulder till both above and below them, and in the 

 overlying unstratified drift were some boulders of granite 

 which must have come from distances of sixty miles at the 

 least.* The j^resence of Tdlina calcarea, and several other 

 northern shells, imjilies a climate colder than that of the present 

 Scottish seas. In the north of Scotland, marine shells have 

 been found in deposits of the same age in Caithness and in 

 Aberdeenshire at heights of two hundred and fifty feet, and 

 on the shores of the Moray Frith, as at Gamrie in Banff, at 

 an elevation of three hundred and fifty feet; and the stratified 

 sands and beds of pebbles whicli belong to the same formation 

 ascend still higher, — to heights of five hundred feet at least.f 

 At much greater heights, stratified masses of drift occur in 

 which hitherto no organic remains, whether of marine or 

 fresh-water animals, have ever been found. It is still an un- 

 decided question whether the origin of all such deposits in 

 the Grampians can be explained without the intervention of 

 the sea. One of the most conspicuous examples has been 

 described b}' Mr. Jamieson as resting on the flank of a hill 

 called Meal Uaine, in Perthshire, on the east side of the valley 

 of the Tummel, just below Killiecrankie. It consists of per- 



* Smith of Jordanhill, Quarterly ceedings of the Geological Society, 



Geological Journal, vol. vi. p. 387, vol. ji. p. 545; and T. F. Jamieson, 



1850. Geological Quarterly Journal, vol. 



t Sec papers by Prestwich, Pro- xvi. 



