2,50 RASAY. GEOLOGY. 



At the northern part and on its eastern side, a culti- 

 vated alluvial soil occupies the interval between the red 

 sandstone and the white sandstone already mentioned 

 which forms the great mass of the island. The inter- 

 mediate substances, if there are any, are thus concealed 

 from observation, and I may indeed add that the surface 

 of the island in general is obscured by similar causes. 

 At its southern extremity two circumstances unite to 

 produce the same uncertainty, the vegetable soil in the 

 interior, and, on the shore, the occurrence of a mass of 

 porphyry, occupying a considerable space and imme- 

 diately following the red sandstone at the point where the 

 connexion must take place. It is however here if any 

 where that it must be sought. 



The strata which are here found near the porphyry 

 consist of a dark bluish micaceous shale, alternating with 

 a coarse limestone of the same colour containing much 

 argillaceous earth, but, as far as I could observe, free 

 from shells. Occasional fragments and indications of the 

 same substances are found in the interior of the island, 

 even as high as the foot of Dun Can hill, but in a manner 

 so dispersed and in portions so minute, as to render it 

 impossible to give them places in the map. To these 

 rocks succeed white sandstone, here also interrupted and 

 obscured by masses of porphyry ; but these being ab- 

 stracted as interfering substances, the regular sequence 

 will appear to be red sandstone, shale and limestone, white 

 sandstone. If this conclusion should appear to be founded 

 on insufficient data, it will be justified no less by general 

 analogy than by a comparison with the series of rocks 

 which occurs in the neighbouring islands, the description 

 of which will appear hereafter. 



The sequence of the upper members of this series is 

 to be seen in many parts of the eastern shore, where the 

 same shale is found in the lowest position, immediately 

 followed by the enormous accumulation of white sandstone 

 which constitutes the high cliffs already described and 



