KERRERA. GEOLOGY. 113 



boisterous sea that so often breaks against them ; forming 

 with it a dreary scene of wildness which is rendered 

 more impressive by the ruins of the ancient castle of 

 Gylen perched on a rocky cliff amid the contention of 

 the winds and waters. 



Although the soil of Kerrera is generally fertile, it 

 is, from the irregularity and the steepness of the hills, 

 principally devoted to pasturage, offering in most places 

 an aspect of permanent verdure. 



THE very disordered positions of the rocks of Kerrera, 

 produce obscurities not easily elucidated in the island 

 itself, but which are rendered clear by an examination 

 of the neighbouring mainland ; a tract in itself sufficiently 

 interesting and intricate to claim much of the attention 

 of a geologist. 



In examining the island it is convenient to commence 

 from the clay slate, on account of the very discontinuous 

 and unconnected state in which the sandstone appears, 

 and the impossibility of tracing its detached portions 

 by any other clue than that of their proximity to this 

 rock. The confusion which will be apparent, will, I trust, 

 prove to be that of nature, not that of the observations ; 

 being only one, out of many instances, of those irregula- 

 rities in the positions of strata, so common where trap rocks 

 form a principal part of the structure of a country.* 



However difficult it may be to trace a continuous 

 extent of argillaceous schist throughout Kerrera, it is not 

 difficult to perceive that it is the lowest rock. It may 

 be observed in many places along the shore, but not 

 along the whole of it ; the secondary strata occupying 

 some parts, and the superincumbent trap descending so 

 deep in others, as to conceal from view that which lies 



* Plate XVI. fig. 3. 

 VOL. II. I 



