226 FRAGMENTS OF SCIENCE 



the other mountains in the neighborhood, all of which 

 would have been clasped by the sea had the sea been 

 there. Here then, and no doubt elsewhere, Mr. Darwin 

 has shown himself to be fallible; but here, as elsewhere, 

 he has shown himself equal to that discipline of surrender 

 to evidence which girds his intellect with such unassail- 

 able moral strength. 



But, granting the significance of Sir Thomas Dick- 

 Lauder's facts, and the reasonableness, on the whole, of 

 the views which he has founded on them, they will not 

 bear examination in detail. No such barriers of detritus 

 as he assumed could have existed without leaving traces 

 behind them ; but there is no trace left. There is detritus 

 enough in Glen Spean, but not where it is wanted. The 

 two highest parallel roads stop abruptly at different points 

 near the mouth of Glen Roy, but no remnant of the bar- 

 rier against which they abutted is to be seen. It might 

 be urged that the subsequent invasion of the valley by 

 glaciers has swept the detritus away; but there have been 

 no glaciers in these valleys since the disappearance of the 

 lakes. Professor Geikie has favored me with a drawing 

 of the Glen Spean '''road" near the entrance to Glen 

 Trieg. The road forms a shelf round a great mound of 

 detritus which, had a glacier followed the formation of the 

 shelf, must have been cleared away. Taking all the cir- 

 cumstances into account, you may, I think, with safety 

 dismiss the detrital barrier as incompetent to account for 

 the present condition of Glen Gluoy and Glen Roy. 



Hypotheses in science, though apparently transcending 

 experience, are in reality experience modified by scien- 

 tific thought and pushed into an ultra experiential region. 

 At the time that he wrote, Sir Thomas Dick-Lauder could 



