THK PARALLEL ROADS Of QLEN ROT. 163 



two highest parallel roads stop abruptly at different points 

 near the mouth of Glen Roy, but no remnant of the barrier 

 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 Profes- 

 sor Geikie has favored me with a drawing of 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 circumstances 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 scientific 

 thought and pushed into an ultra experiential region. At 

 the time that he wrote, Sir Thomas Dick-Lauder could not 

 possibly have discerned the cause subsequently assigned for 

 the blockage of these glens. A knowledge of the action of 

 ancient glaciers was the necessary antecedent to the new 

 explanation, and experience of this nature was not pos- 

 sessed by the distinguished writer just mentioned. The 

 extension of Swiss glaciers far beyond their present limits, 

 was first made known by a Swiss engineer named Venetz, 

 who established, by the marks they had left behind them, 

 their former existence in places which they had long forsaken. 

 The subject of glacier extension was subsequently followed 

 up with distinguished success by Gharpentier, Studer, and 

 others. With characteristic vigor Agassiz grappled with it, 

 extending his observations far beyond the domain of Switz- 

 erland. He came to this country in 1840, and found in 

 various places indubitable marks of ancient glacier action. 

 England, Scotland, Wales, and Ireland he proved to have 

 once given birth to glaciers. He visited Glen Roy, surveyed 

 the surrounding neighborhood, and pronounced, as a conse- 

 quence of his investigation, the barriers which stopped the 

 glens and produced the parallel roads to have been barriers 

 of ice. To Mr. Jumieson, above all others, we are indebted 

 for the thorough testing and confirmation of this theory. 



And let me here say that Agassiz is only too likely to be 

 misrated and misjudged by those who, though accurate 

 within a limited sphere, fail to grasp in their totality the 



