Ml. 67.] THE PARALLEL ROADS OF GLEN ROY. 299 



wafer. This I quite admit in my paper, and refer the upper 2 

 to 3 feet of the road to this origin ; but that they were entirely 

 formed in this way is scarcely possible, because 



1. The talus was too temporary. 



2. There is no wear. 



3. No cliff talus. 



4. ISTo difference in the slopes. 



5. And the waved line of the roads is incompatible with 



shore-origin in the first place. 



How could a shore-line be 10 to 12 feet above the water-level 

 in one case, and 8 to 10 feet below it in another ? If a sub- 

 aerial talus caused the difference, the roads would suffer inter- 

 ruption in their level, which they don't. T must make this clear 

 in my paper. ... I am sincerely yours, 



JOSEPH PRESTWICH. 



J. Prestwich to the Same. OXFORD, 12th May 1879. 



MY DEAR EVANS, With regard to what you say in your last 

 note as to why the terraces may now be uneven 



1. If the rise in the land had not been uniform. Yes ; but all 



the terraces would then have had the same curve, whereas 

 each terrace has its own curve. 



2. If some parts of the shore had slipped. There are no traces 



of this. 



3. The difficulty of conceiving a slip on so large a scale. I see 



no limit except the absence of similar favourable condi- 

 tions. So long as they obtain, so far would the terraces 

 extend. The more I think of it, the more inevitable does 

 the slip appear. 



The whole mass of detritus being saturated, and being at 

 an angle greater than the angle of repose of the detritus in a 

 saturated condition, would at once slip when set in motion. 

 But the outflow of water gradually lessening, the fall would be 

 gradually checked. 



Then again the detritus gradually left dry would, as it drained 

 by degrees, acquire a higher angle of repose owing to the circum- 

 stance of the water draining from it in innumerable rills. With 

 the loss of water the angle of repose would become greater. . . . 



