SCALPA. GEOLOGY. 



occupying the same positions ; while in the interval they 

 are found with a perfect identity of structure and position, 

 in Longa and in the rock Scuir Dearg.* If again they 

 are prolonged in the opposite direction they meet v/ith 

 the island of Soa and with the shore at Loch Scavig, 

 where the same sandstone also occurs. Still further, the 

 island of Rum presents the same strata ; occupying how- 

 ever a breadth transverse to the line of bearing, which 

 includes part of the limestone tract of Sky and that of the 

 neighbouring islands. t The whole may therefore be con- 

 sidered as the interrupted portions of one set of beds ; the 

 interruption being partly the result of that depression which 

 admits of the superiority of the sea, and partly arising 

 from the superincumbent syenite ; while to both of these 

 causes is possibly added a disturbance connected with 

 the deposition of the syenite and trap, of which there are 

 not wanting other evidences. In the next place it must 

 be remarked that there is a perfect identity in the mineral 

 characters of this line of sandstone and that of the Kyles 

 district of Sky,f although they are separated by the calca- 

 reous tract ; and that the sandstone is of a peculiar cha- 

 racter, as has already appeared from the examination of 

 Sky. Lastly it must be recollected that if the island of 

 Rum be admitted into this tract, its breadth will be found 

 to reach nearly from the first portion of the sandstone, 

 or that which is next to the gneiss of Sky, to the second 

 or that which constitutes Soa, Scalpa, the Croulin isles, 

 and the mainland about Loch Toskig. The blank caused 

 by the sea between Rum and Sky, prevents the connexion 

 from being drawn closer. || 



It is now proper to examine how these facts bear 

 upon the question which concerns the relative positions 

 of the limestone of Scalpa, and consequently that of the 



* See the Map of Sky. t See the general Map. 



* The eastern portion cut off by a line from Lucy to Loch in Dual. 

 II Plate XV. 



