264 DATE OF GLEN ROY TERRACE-LINES. CHAP. xni. 



feet beneath the sea, suhsequently to the first great glaciation 

 of Scotland (p. 244). Yet that amount of subsidence might 

 have occurred, and even a more considerable one,, without 

 causing the sea to rise to the level of the lowest shelf, or to 

 a height of 850 feet above the present sea-level. 



This is a question on wliich I am not prepared at present 

 to oflFer a decided opinion. 



Whether the horizontality of the shelves or terrace-lines is 

 really as perfect as has been generally assumed, is a point 

 which will require to be tested b}' a more accurate trigono- 

 metrical survey than has jet been made. The preservation 

 of precisely the same level in the lowest line throughout the 

 Glens of Roy, Spean, and Laggan,for a distance of twenty miles 

 east and west and ten or twelve miles north and south, would 

 be very wonderful if ascertained with mathematical precision. 

 Mr. Jamieson, after making in 1862 several measurements 

 with a spirit-level, has been led to suspect a rise in the lowest 

 shelf of one foot in a mile in a direction from west to east, or 

 from the mouth of Glen Eoj'' to a point six miles east of it in 

 Glen Spean. To confirm such observations, and to determine 

 whether a similar rate of rise continues eastward as far as the 

 pass of Muckul, would be most important. 



On the whole, I conclude that the Glen Roy terrace-lines 

 and those of some neighboring valleys were foi*med on the 

 borders of glacier-lakes, in times long subsequent to the prin- 

 cipal glaciation of Scotland. They may perhaps have been 

 nearly as late, especially the lowest of the shelves, as that 

 portion of the post-pliocene period in which man coexisted in 

 Europe with the mammoth. 



