The Parallel Beads of Glen Hoy. 401 



shelves ; and that they must escape, notice in many cases where 

 they do exist, from the fointness of their appearance, and be- 

 cause they were not looked for. When Mr Darwin's specu- 

 lations become known, we have no doubt that remains of 

 terraces will be found in a hundred places where then- ex- 

 istence has never been suspected. He accounts for the non- 

 appearance in Glen Spean of the two upper terraces of Glen 

 Roy, by observing, that when the water stood at the level of 

 these terraces, Glen Spean would communicate with Gleu 

 Spey, and being then a channel connecting opposite seas 

 would be traversed by strong cm-rents. He shews that a 

 slight variation of cu-cumstances makes any of the three 

 terraces in Glen Roy disappear for a considerable space ; that 

 an intermediate terrace between the second and third once 

 existed, of which only a smaU remnant is discoverable ; that 

 on the supposition of the waters receding slowly, an indefinite 

 succession of little terraces would be formed, which would 

 blend with the alluvial cover, and be undistinguishable from 

 It, except at some parts where conditions very favourable to 

 the generation of terraces existed ; that the existence of a 

 terrace in Glen Gloy twelve feet above the highest in Glen 

 Roy, may be explained either in this way, or by the different 

 height of the tides, as in the Strait of Magellan, where the 

 tide rises twenty feet at one part, and forty at another some 

 miles farther on. The sum of his argument is expressed in 

 the general remark, that the obliteration of the terraces may 

 be regarded as the natural and usual result— their preser- 

 vation as an exception, arising from peculiar and favourable 

 circumstances. 



Erratic blocks belonging to distinct localities are found 

 both imbedded in, and resting on, the terraces. He supposes 

 that masses of floating ice caught up these stones, and having 

 stranded on the terraces, dropt them there. He found some 

 at an elevation of 1000 feet above the upper terrace in Glen 

 Roy, shewing that the water had once stood at that height. 

 His remarks on the water-worn isthmuses connecting the val- 

 leys of the Roy, the Spey, and the Gloy, on the buttresses of 

 gravel at the tributary streamlets, and on the deep alluvium 

 in the bottom of these valleys, we have not room to speak of. 



