246 ISLA. GEOLOGY. 



and will be described more properly hereafter in situa- 

 tions where they are more conspicuous and important. 



The strata thus described as extending from the western 

 side of the island to the Mull of Oe on the east, can 

 be traced in contact and in obvious succession throughout 

 this whole space. It will not therefore be useless to 

 review the whole alternation before proceeding to the 

 description of the remaining rocks which occupy more 

 limited spaces. Omitting the minor repetitions, it is as 

 follows : clay slate, gneiss, clay slate, graywacke slate, 

 clay slate, quartz rock, coarse graywacke, quartz rock, 

 clay slate, micaceous schist, clay slate. 



It is now necessary to describe those rocks which are 

 more obscure in their structure and position. The causes 

 of that obscurity will be found to depend on the place 

 they occupy in the island, on the nature of their dispo- 

 sition, on the forms of the surface^ and on its encumbered 

 state. The most remarkable of them do not reach the sea 

 shore so as to display their sections, nor is it possible to 

 obtain a continuous view of any portion of them. By 

 the aid of analogy they may perhaps be referred to their 

 true geological positions. 



The principal, and the most extensive of these rocks 

 is the limestone, which chiefly occupies the middle divi- 

 sion of the island. Its general extent will be seen in the 

 map better than it could be understood in description, but 

 an accurate limitation of that space is impossible, on account 

 of the depth and fertility of the soil. There are three 

 kinds of this limestone, and such is the nature of their 

 several characters and connexions, that each requires a 

 separate consideration. 



The first and most extensive is the blue schistose va- 

 riety^ which forms perhaps nine tenths of the whole. Both 

 the geological and mineral characters of this rock are 

 familiar to all those who are acquainted with the Scottish 

 Highlands ; as it is of frequent occurrence, and is found, 

 other places, in Lismore, It occupies an irregular 



