REMARKS ON GLEN ROT. 17 



only add that I subsequently paid a visit to the locality in order to 

 measure the height which the beds of water-rolled pebbles attain 

 above the bottom of the col. This I found to be 25 feet. The col 

 itself is 848 feet above the sea at its lowest point, and the highest 

 beds of pebbles I saw beside it reach up to 873 feet, which would 

 seem to show that a large deep river went out here. These pebble- 

 beds lie a little to the eastward of the watershed. The descent or 

 faU from this col to the Spey along Strathmashie is for the most part 

 very gentle, and the bottom of the Spey valley itself all along from 

 Cluny MacPherson's castle past Laggan is a swampy meadow which 

 may possibly be the bed of an old lake filled up with silt. 



IX. Height and horizontality of the ' Eoads.' 



Each of the Parallel Eoads consists of a sort of terrace or shelf, 

 generally from 40 to 70 feet broad, and sloping towards the middle 

 of the glen at angles varying from 5° to 30°. 



Now, in regard to the heights given upon the Ordnance map, it 

 must be borne in mind that the figures refer to points taken along 

 the middle of each terrace, that is to say halfway between the upper 

 and nether border of the ribbon-like mark which runs along the 

 hill-sides. Assuming the vertical measurement of each terrace to 

 vary from 4 to 16 feet, a series of stations taken along the middle 

 would range from 2 to 8 feet below the upper edge, and as the 

 surface of the water probably corresponded with the upper edge of 

 the terrace (or may perhaps have been higher, owing to the crum- 

 bling down of debris upon its original upper border) these stations 

 would therefore be from 2 to 8 feet beneath the ancient level of the 

 lake, and lower sometimes than the col or outlet to which the road 

 corresponds. The Ordnance figures are consequently somewhat 

 misleading as to the exact height of the water, and this discrepancy 

 in relation to the cols has probably been increased by the fact that 

 the cols themselves in most cases are now overgrown with peat or 

 turf which has raised their surface higher than it was when the 

 lakes existed. Por example, Mr. Milne-Home ^ found the peat on 

 the Glen Gluoy col to be 5| feet thick. It is evident the lake must 

 have rather exceeded the height of its col, otherwise the water would 

 not run out ; whereas the Ordnance heights, owing no doubt to the 

 circumstances I have mentioned, frequently indicate a Parallel Eoad 

 as running a few feet lower than its col. 



These ' roads,' although wonderfully clear when viewed from a 

 distance under favourable light, are nevertheless often very obscure 

 when we come to stand upon them. Sometimes indeed they seem 

 to vanish altogether in ghost-like fashion, so shadowy and vague 

 is the outline of what remains. The clearness of the lines at a dis- 

 tance seems to depend upon some subtle difference in the shade of 

 light or colour, due either to alteration of the angle at which the 

 surface is presented to the light or to some change in the character 



1 Trans. Eoy. Soc.Edin. vol. xxvii. (1876) p. 597. 

 Q. J. G. S. No. 189. c 



