OBSERVATIONS 



ON 



THE GEOLOGY 



OF THE 



WESTERN ISLES OF SCOTLAND. 



INTRODUCTORY REMARKS ON THE GENERAL DIS- 

 POSITION OF THE WESTERN ISLANDS. 



FOR the purpose of rendering the physical description 

 of these islands more intelligible in a topographic view, 

 and more interesting to the geologist in a scientific one, 

 I have divided them into five distinct groups. These are 

 distinguished by the names of the Gneiss, the Trap, the 

 Sandstone, the Schistose, and the Clyde islands-*. The 

 four first are associations strictly natural, since a com- 

 munity of structure, with a considerable geographical con- 

 nexion, pervades each group. The last is founded chiefly 

 on geographical community of position in the islands it 

 includes ; although, even in this, certain common characters 

 will be found in a greater or less degree to predominate 

 through the whole. By treating of them in this manner 

 the relations which they bear to the continent of Scot- 

 land will be the more readily understood ; while from the 

 great length of line they occupy on the western coast, 

 and the analogy of their structure and disposition to 

 those of the continental strata, they will be found to illus- 

 trate in a very considerable degree its geological history. 



It is impossible to cast our eyes on the map without 

 being struck by the general north-easterly tendency, nqt 



* To these have been added two distinct articles, which could.not be 

 included in either division. 



VOL. I. ft 



