210 FRAGMENTS OF SCIENCE. 



collect. The surface of the lake thus formed would 

 gradually rise, until it had reached the level of the 

 col which divides Glen Eoy from Glen Spey. Here 

 the rising of the lake would cease; its superabundant 

 water being poured over the col into the valley of the 

 Spey. This state of things would continue as long as 

 a sufficiently high barrier remained at the mouth of 

 Glen Eoy. The lake thus dammed in, with its surface 

 at the level of the highest parallel road, would act, as 

 in Glen Gluoy, upon the friable drift overspreading the 

 mountains, and would form the highest road or terrace 

 of Glen Eoy. 



And now let us suppose the barrier to be so far 

 removed from the mouth of Glen Eoy as to establish a 

 connection between it and the upper part of Glen 

 Spean, while the lower part of the latter glen still con- 

 tinued to be blocked up. Upper Glen Spean and Glen 

 Eoy would then be occupied by a continuous lake, the 

 level of which would obviously be determined by the 

 col at the head of Loch Laggan. The water in Glen 

 Eoy would sink from the level it had previously main- 

 tained, to the level of its new place of escape. This 

 new lake-surface would correspond exactly with the 

 lowest parallel road, and it would form that road by its 

 action upon the drift of the adjacent mountains. 



In presence of the observed facts, this solution com- 

 mends itself strongly to the scientific mind. The 

 question next occurs, What was the character of the 

 assumed barrier which stopped the glens? There are 

 at the present moment vast masses of detritus in cer- 

 tain portions of Glen Spean, and of such detritus Sir 

 Thomas Dick-Lauder imagined his barriers to have 

 been formed. By some unknown convulsion, this de- 

 tritus had been heaped up. But, once given, and once 

 granted that it was subsequently removed in the man- 



