82 Prof. Forbes on (he Topography and Geology of the 



which I observed. But to make the best use of my oppor- 

 tunities, I have computed the height of the Cuchullin hills 

 on two suppositions : first, by an interpolation of the appa- 

 rent change in the height of the mercury at Sligachan ; and, 

 secondly, by direct comparison of my observation on the sum- 

 mit of the Scuir-na-Gillean with MrNecker's almost simul- 

 taneous observation at Portree. The first computation gives 

 3193 feet for the height above Sligachan Inn ; the second 

 3115 feet above Mr Necker''s house at Portree. But the 

 first is 30 or 40 feet above the sea-level, the latter 80 or 90 : 

 the result, therefore, is nearly coincident, and it is probable 

 that the true height of Scuir-na-Gillean is between 3200 and 

 3220 feet.* Bruch-na-Fray is probably about 40 feet lower. 

 The Cuchullin range is completely detached from the 

 Red hills and from Ben Blaven by the vale of Glen Sliga- 

 chan, and their boundary on the other sides is not less well 

 marked ; the ocean, at Scavig Bay, washing their base, 

 whilst on the west and north, they slope rapidly down to the 

 level of the plateaux of common trap, which form the larger 

 part of the island ; and the general direction of another arm 

 of the sea, Loch Brittle, also skirts their western slope. It 

 is possible to walk completely round the Cuchullin group, 

 and I have done so, as well as intersected it in several direc- 

 tions. As far as I can infer from the writings of geologists,, 

 this has not been done before ; but Mr Jameson Torrie 

 walked, I believe, from Sligachan, by Loch Scavig, to Brittle, 

 which is by far the most toilsome part. As to Dr MacOul- 

 loch, it is impossible to avoid alluding to the disagreeable 

 uncertainty with which, in attempting to localize his de- 

 scriptions, we find them shrouded in an impenetrable veil of 

 indefiniteness and mystery, which makes it impossible to dis- 



* A record of a measurement of Scuir-na-Gillean, professing to be baro- 

 metrically made in 1844, was pointed out to me on the window shutter of 

 the inn at Sligachan, indicating 3104 feet, which, it will he seen, is not 

 far from the truth. I have since learnt, however, from the author of this 

 observation, that he did not succeed in attaining the highest point within 

 (as he estimated) 200 feet of the vertical ascent, a circumstance which 

 ought, undoubtedly, to have been mentioned, as rendering the seeming 

 precision of the measurement illusory. 



