HASAY. GENERAL DESCRIPTION. 239 



RASAY.* 



THE natural affinity of composition subsisting between 

 the northern division of this island and Rona, has, toge- 

 ther with their intimate geographical connexion, induced 

 me to describe it next in the order of succession, and 

 first therefore of the Trap islands. By adopting the 

 course which I have followed in this and other cases, 

 although the order of arrangement may at first sight often 

 appear capricious, it will be seen that considerable facility 

 is afforded towards understanding, not only the structure 

 of the -individuals, but the more important relations they 

 bear to each other ; as well as in reducing their scattered 

 and insulated materials into one whole. There are many 

 obscurities in the composition of one island which can 

 only be removed by the knowledge of another ; and by 

 thus proceeding from a base to a superstructure, the 

 reader will immediately comprehend many points which 

 I did not arrive at till after much circuitous labour and 

 many comparisons. Sky, the most prominent and import- 

 ant feature in this group, is, from its construction, from 

 the scattered nature of its details, and from the frequent 

 disappearance of the regular strata in consequence of the 

 presence of the irregular rocks, a fund of obscurity ; while, 

 being the centre to which so many parts tend, it is the 

 most in need of illustration. Rasay, though interesting 

 also in itself, becomes here a principal object, by its 

 collateral and secondary uses ; and its value in this 

 respect will be hereafter apparent when I shall attempt 

 to investigate the structure of the former island.f 



* Rasay Raasay, properly from Raa, a roe or deer. Danish. See 

 the Map of Sky. 



f So much in geological investigation depends on the truth of maps, 

 that there is great reason to lament the general incorrectness of the 

 maps and charts of this coast. In no instance is the defect more 



