54 



have done, until greater certainty is attained with regard to the 

 species to which the leaves and lignites are to be referred. It is not 

 then improbable, that our Bute trap formation, with its ochres and 

 lignites, may also be of tertiary age, though overlying the older 

 secondary strata. 



The chemical composition of ochre is almost exactly the same 

 as that of basalt ; 100 parts consist of silex 56'40, alumina 3'46, 

 per-ox. iron 24'14, carb. lime 0'90, water 15 '10. It is in fact a 

 decomposed basalt, partially refused and reconsolidated by the suc- 

 ceeding flow of igenous matter. 



38. The Kilchattan limestone already referred to is the most 

 considerable mass on the island. It is a cornstone subordinate to 

 the old red sandstone ; the strata of the two rocks are conformable, 

 and the dip nearly south at a moderate angle. At the summit of the 

 ridge near the picturesque ruins of the ancient castle of Kelspoke 

 the sandstone over the limestone is seen dipping under the trap 

 which bounds the rugged terraced ridges descending towards Garroch- 

 head on the south coast. These ridges have the same inclination 

 southwards as the underlying sandstone strata, and present a sue. 

 cession of bold fronts towards the north. The sandstone appears to 

 have had its present inclination when the submarine lava streams, 

 of which these ridges consist, were poured out over it ; the scarped 

 fronts were no doubt formed by the action of currents when the 

 land was rising. The arrangement of the strata at Kilchattan is 

 shown in the annexed cut.* No fossils were found in the limestone. 



(a, 6) Sandstone; (c) limestone; (d) trap. 



39. The dikes of Bute are composed of greenstone, or basalt, and 

 are very numerous, especially on the east coast. They traverse the 

 strata in various directions, and in some cases can be traced for several 

 miles continuously, preserving nearly the same width and direction 

 throughout, t Two or more are sometimes seen to meet and coalesce 



* This and the other cuts illustrative of Bute are copied, by permission, from the 

 Journal of the Glasgow Philosophical Society for 1848. 



f A dike seventy feet wide emerges from the sea at the mineral well near Bogany point, 

 and ranging nearly west is seen in Huntly Place, where it has been largely quarried ; 

 interrupted by the bay it rises again, is conspicuous across the high grounds west of the 

 town, and crossing the island, enters the sea at Ettrick bay. Here another dike, two 



