CHAP. XIII. PARALLEL ROADS OF GLEN ROY. 263 



is about 850 feet high ; for in that ease the remarkable per- 

 sistency and integrity of tlie roads and deltas, befoi-e described, 

 must have been impaired. 



We have seen (p. 244) that fifty miles to the south of 

 "Lochaber, the glacier formations of Lanarkshire with marine 

 shells of arctic character have been traced to the height of 

 524 feet. About fifty miles to the southeast in Perthshire 

 are those stratified clays and sands, near Killiecrankie, which 

 were once supposed to be of submarine origin, and which in 

 that case would imply the former submergence of what is now 

 diy land to the .extent of 1550 feet, or several hundred feet 

 beyond the highest of the parallel roads. Even granting 

 that these laminated drifts may have had a different origin, 

 as above suggested (p. 246), there are still many facts con- 

 nected with the distribution of erratics and the sti'iation of 

 rocks in Scotland which are not easily accounted for without 

 supposing the country to have sunk, since the era of conti- 

 nental ice, to a greater depth than 525 feet, the highest point 

 to which marine shells have j^et been traced. 



After what was said of the pressure and abrading power of 

 a general crust of ice, like that now covering Greenland, it 

 is almost superfluous to say that the parallel roads must 

 have been of later date than such a state of things, for every 

 trace of them must have been obliterated by the movement of 

 such a mass of ice. It is no less clear, that as no glacier-lakes 

 can now exist in Greenland, so there could have been none 

 in Scotland, when the mountains were covered with one great 

 crust of ice. It may, however, be contended that the parallel 

 roads were produced when the general crust of ice first gave 

 place to a period of separate glaciers, and that no period of 

 deep submergence ever intervened in Lochaber after the 

 time of the lakes. Even in that case, however, it is diflScult 

 not to suppose that the Glen Eoy country participated in the 

 downward movement which sank part of Lanarkshire 525 



18 



