47 



VII. THE CLYDE ISLANDS. 

 BUTE. 



34. A pretty full and generally accurate account of the geology of 

 Bute has been given by Dr. MacCulloch in his work on the Western 

 Isles, published in" 1819. For thirty years after, no observations, 

 so far as we can learn, were put on record respecting it, except some 

 notices of its remarkable coast terrace and raised shelly deposits by 

 Mr. Smith of Jordanhill. The greater variety of the strata in 

 Arran, and the bearing of the phenomena there exhibited upon 

 questions in theoretical geology actively discussed at the time, drew 

 attention entirely to that island, and Bute, in common with other 

 parts of the West of Scotland, was overlooked. Yet it has many 

 points of great interest ; strata occur here to be met with nowhere 

 else in Scotland ; and the effects of its trap dikes upon the adjoining 

 strata, are without parallel in the history of theoretical geology. 

 The phenomena to which we allude were not observed by Dr. 

 MacCulloch ; and were first made known to geologists in two papers, 

 published in The Transactions of the Glasgow Philosophical Society 

 for 1848, and The London Philosophical Magazine for August, 

 1849. We shall first briefly notice the general structure of the 

 island ; and then describe at greater length the remarkable changes 

 referred to, and those strata to be seen nowhere else, and therefore 

 more worthy of the student's attention. 



35. Three deep depressions or valleys traverse Bute perpendicularly 

 to its longer axis, dividing the island into four portions, and marking 

 the boundaries of as many distinct geological formations. They 

 terminate on either side in bays or indentations of the land, formed 

 here as in most other cases at the points of least resistance, the 

 junctions, namely, of dissimilar strata. Those on the east side are 

 the well known sheltered bays of Kames, Bothesay, and Kilchattan. 

 The low tracts in question show no rock in situ, but are filled with 

 shingle and alluvial deposits concealing the junctions, strata of 

 peat, and occasional shell beds. The deposit already referred to 

 (Art. 5), as described by Mr. Miller in The Witness of July, 1855, 

 lay in the Bothesay valley ; and a similar one with numerous shells 

 has since been found in the valley at Kames bay. These have not 

 yielded any additional species to those found by Mr. Smith, and 

 already given in our list. The elevation above the sea level has been 

 shown by Mr. Bobert Chambers in his interesting and beautifully 

 illustrated work on ancient sea margins, nowhere to exceed thirty 

 feet ; and as this is also very nearly the height of the terrace already 



