58 COLONSAY 



and it is not proposed here to enter into its discussion 

 further than to note some of its relations to the landscape 

 and flora of Colonsay. The difficulties encountered by any 

 other than a geologist in tracing certain rocks through the 

 island, owing to the superficial resemblance the different 

 varieties bear to one another and their lack of distinctive 

 features, are greatly increased by the many intermediate forms 

 which they assume. Irregularities in topography and in the 

 outcropping of the rocks also occur, which are sufficiently 

 great to perplex the novice in his pursuit of practical 

 geology in the field, and to prevent him, if left to his own 

 resources, from ever discovering the key to the stratigraphical 

 problem of the islands. A coloured geological map, kindly 

 lent by Messrs Wright and Bailey, prepared after the recent- 

 survey of the island by the Geological Department, enabled 

 the writer to follow up the principal rocks throughout the 

 island, with a view to ascertaining the influence (if any) 

 exerted by the underlying strata on the surface vegetation, 

 referred to more in detail elsewhere. 



Colonsay and Oransay are, as already stated, mainly 

 composed of sedimentary rock of Lower Torridonian age. 

 They consist of " alternating series of grits, flags, and mud- 

 stones, with a well-marked bed of sandy limestone near the 

 top." l The strike is approximately north-east and south-west, 

 and the prevalent dip towards the east. "The Colonsay 

 limestone, which, with the beds above and below it, 

 constitutes an easily recognisable horizon, occurs on the 

 eastern coast of the island, dipping out to sea at a low angle." 

 An almost continuous succession from higher to lower beds 

 is passed over as one proceeds westwards or southwards from 

 the limestone, " and on finally reaching the extreme outlying 

 parts of Oransay and Ardskenish there is still no indication 



F.G.S. (Q 

 p. 297). 



The Two Earth-Movements of Colonsay," by W. B. Wright, B. A. , 

 . (Quarterly Journal of the Geological Society, vol. Ixiv. No. 254 



