Mr. Bryce on the Geology of the Island of Bute. 199 



These low tracts terminate on either side of the island in deep bays, 

 or indentations of the land, between which, there can be no doubt, as 

 well from the lowness of the ground, as from the marine character of the 

 materials of which these tracts are composed, the sea once flowed, thus 

 forming three straits or narrow channels, dividing Bute into four islands. 

 1 liavo no means, either from a personal survey or otherwise, of stating 

 with even tolerable precision, what amount of elevation was required to 

 convert these narrow straits into dry land ; it is probable that it was the 

 same as that which was realized when Loch Lomond was placed at its 

 present level above the Clyde ; not, however, by one sudden movement, 

 but by a succession of slow and gradual movements, such as there is 

 reason to think may be still going on in some parts of Scotland, and as 

 are well known to have been long in progress, to a great extent, in the 

 Scandinavian peninsula.* 



Another interesting feature in the structure of Bute, and one intimately 

 connected with the origin of the low tracts referred to above, is the 

 terrace which surrounds almost the whole island, at a considerable height 

 above high water mark, and along which the road is conducted throughout 

 almost the whole extent of the coast. The cliffs which in many parts rise 

 above the terrace are often worn into caves, and bear other obvious marks 

 of the action of the waves. This terrace is, no doubt, the former beach. 



No. 2. 



a, present sea level; b, terrace urith road; c, inland sea-worn cliff. 



It is well marked along the opposite coast from Gourock to Largs, in the 

 Cumbrays, in Arran, and upon most of the estuaries in the firth of Clyde. 

 Taking this along with other evidence, accumulated by Mr. Smith of 

 Jordan-hill in various papers, wo cannot hesitate to admit, that at a 

 comparatively recent period such a change of level has been effected in 

 Bute as to convert a detached group of islands, separated by narrow and 

 not very deep straits, into continuous land. 



3. The valleys which have been now described are the boundaries 



* Loch Lomond is about 22 feet above the Clyde. It is specially referred to because 

 wo haw, in tli. country between it and the Clyde, the evidence derived from shelly 

 deposits, — which is much more satisfactory. 



