314 Dr Ch. Martins on the Marks of Glacial Action 



the stronger repelled the weaker. This we actually witness 

 in the existing glaciers, and in particular upon that of the 

 Aar, and the Mer de Glace of Chamouni. The plain of Swit- 

 zerland presents the same anomalies ; and it is often very 

 difficult to assign reasons for the direction of the striae, be- 

 cause it was so overwhelmed with glaciers, which mutually 

 crowded, repelled, and disturbed each other. Thus, then, 

 without attempting to disparage the difficulty resulting from 

 the direction of the striae discovered to the south of Edin- 

 burgh, I believe they will not prove an insuperable objection 

 against the alleged influence of the glaciers. And more ; I 

 am convinced that the Scottish geologists, in attentively ob- 

 serving the direction of all the visible striae between the 

 Friths of the Clyde and of the Forth, and in comparing them 

 with the origin of the transported boulders, will be able ex- 

 actly to trace upon a map the limits of the glaciers which 

 had invaded the plain, and so will be able to give a complete 

 account of the direction of the striae which run from west 

 to east. 



Wehave just seen that the rocks of Scotland are covered with 

 striae identical with those which mark existing glaciers : and 

 we now remark that these striated rocks are covered over by 

 a clay which contains striated pebbles. If you dig beneath 

 one of the glaciers of Switzerland, that of Grindelwald or of 

 E-osenlaui for example, you will find exactly the same thing. 

 Before you discover a polished rock you will be obliged to 

 remove a thick bed of mud and of pebbles, which is the 

 boulder-clay of Scotland in miniature. The striae which 

 cover these pebbles prove that, from the moment they were 

 striated, they — ^the pebbles — have not been water-rolled. 

 The clay or till, which is the analogue of the mud of the 

 glacier, and of the lehm and loess of Swiss geologists, 4s the 

 result of the complete trituration of rocks by the glaciers. 



The environs of Edinburgh, then, present three of the 

 characteristic signs which a glacier leaves behind it, — the 

 polished rocks, the striated pebbles, and the glacier mud. 

 We shall also find transported blocks, though no veritable 

 moraines. In explanation of this apparent anomaly let us 

 recal to recollection the manner in which the moraines are 



