480 RUM. GEOLOGY. 



following them. As the disturbance of the magnetic 

 needle is in this island considerable, I cannot be assured 

 that the bearings of the strata are very precisely con- 

 tinuous with those of the sandstone of Sky. Yet they 

 appeared such in those places where they presented the 

 most continuous extent, and where they were at the 

 greatest distance from the trap rocks. I have accordingly, 

 in the subjoined map, laid them down as north-easterly 

 throughout the island; a rule which will be found to 

 hold good to the north of Loch Scresort, and to require 

 modification only in those places where they display a 

 less extent, and are immediately in contact with the 

 masses of trap that form the mountains. It is super- 

 fluous to state the probable cause of these exceptions, 

 the subject having so often already fallen under notice 

 in different places. Under similar exceptions the dip 

 of the strata is also to the westward ; the angles of eleva- 

 tion being generally considerable, but varying in different 

 places as they do in Sky. Whether the strata are pre- 

 cisely rectilinear or not with those of Sky, there can be 

 little doubt of their general identity of position ; nor any 

 reason to hesitate in considering both of them as portions 

 of one deposit separated by the intervening sea. Thus, 

 as I have already pointed out, the same rocks will be 

 found reaching with little, if any, disturbance of position, 

 from Rum through Sky and Scalpa to the Croulin islands 

 and to the mainland : a connexion which is indicated 

 in the general Map. 



I had not the good fortune to observe in Rum any 

 of those secondary strata which in Sky are superimposed 

 on 'the red sandstone; although I searched for them 

 among the uppermost beds in those parts of the island 

 where they might be expected. It is probable that they 

 do not exist, since the avidity with which calcareous rocks 

 are sought for by the farmers throughout the islands, 

 would necessarily have led to the discovery, either of 

 the gryphite limestone which in Sky follows the sandstone. 



