GEOLOGY OF BUTE. 337 



certain trifling local deflections, passed out into the channel 

 which divides Bute from Arran. He holds strongly the 

 view that the granite boulders one sees along the S. and 

 S. W. shores of Bute are not from Arran, but are ship ballast 

 tossed overboard and washed up. He maintains also that 

 the statement recently put forth, that Arran granites are 

 found on the Cantire coast, is certainly erroneous ; and that 

 a northern or north-eastern origin must be sought for them. 

 We have not studied the island so carefully as to pronounce 

 any positive opinion on this point; but certainly there is 

 no extensive elevated surface in Bute to which we could 

 look as a snowfield, or birth-place of glaciers. 



Features of the 



144. The facts above stated point to a considerable 

 and extensive depression of the laud, as the highest 

 beds with shells reach 510 feet, and are as far inland as 

 Airdrie; yet this amount of depression would preserve all the 

 dominant features of the land in the west of Scotland. There 

 must have been an inner sheltered estuary and an outer open 

 and stormy margin. This is shewn as well by the contrasted 

 state of the shells, much broken in the Arran beds, perfect 

 and well preserved even in the most delicate species in the 

 beds of the inner frith and of Clydesdale, as by the absence 

 of the laminated clay in Arran, and in other places, such 

 as Lochgilphead, which must have been exposed in the 

 state of the surface imagined by us. Clydesdale, in fact, 

 formed a gulf sheltered by the Lennox hills and coast 

 range of Renfrew, and was connected to the outer waters 

 by a strait below Erskine, and a long narrow channel in 

 the direction of the Dairy valley. Bute and the con- 

 nected isles would form, for a long period, a low archipel- 

 ago, sheltering the inner frith; Bute itself consisting of four 

 islets. Cantire was crossed by several channels, admitting 

 the ocean one of them debouching upon Lochgilphead, in 



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