THE 



LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



AUGUST 1849. 



XI. Oti the Lignites and Altered Dolomites of the Island of 

 Bute. By James Bryce, Jun,^ M.A., F.G.S.* 



I. Introduction. 



I. npHE only account which we possess of the geology of 

 A Bute is that given by Dr. MacCulloch in his " De- 

 scription of the Western Islands of Scotland." During the 

 thirty years that have elapsed since the publication of that 

 work, no observations that I am aware of have been put on 

 record, either supplementary to this account or in correction 

 of it. Indeed the island seems to have been entirely over- 

 looked ; the superior grandeur and interest of the sister isle 

 of Arran having wholly absorbed the attention of geologists. 

 Yet Bute has many points of great interest in itself; and phae- 

 nomena which in Arran are but obscurely shown are here 

 fully exhibited. During a residence in the island for a part 

 of last summer, I had frequent opportunities of testing the 

 accuracy of Dr. MacCulloch's account; and it is but justice 

 to the memory of that distinguished geologist to say, that I 

 have found the description of the phaenomena to agree very 

 closely with my own observations; and his work to be, here 

 as well as in other places, a safe and pleasant guide. 



II. Corrections and Supplementary Remarks. 



2. The island of Bute is naturally divided into four por- 

 tions, by three deep depressions or valleys, which traverse it 

 perpendicularly to its greatest length. These low tracts ter- 

 minate on either side of the island in deep bays, 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 



* Communicated by the Author. 

 Phil. Mag. S. 3. Vol. 35. No. 234. Aug. 1849. G 



