264 DATE OF GLEN EOT TERRACE LINES. CHAP. xm. 



feet beneath the sea, subsequently 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 which I am not prepared at present 

 to offer a decided opinion. 



Whether the horizontally of the shelves or terrace-lines is 

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

 which will require to be tested by a more accurate trigono 

 metrical survey than has yet been made. The preservation 

 of precisely the same level in the lowest line throughout the 

 Grlens 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 Grlen Roy to a point six miles 

 east of it in Grlen 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 Grlen Roy terrace-lines 

 and those of some neighbouring valleys, were formed on the 

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

 principal 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. 



