1GO GARVELOCH ISLES. GEOLOGY. 



all more or less rounded, as if from previous attrition. 

 Where the schistose beds approach to the limestone, a 

 gradual change of the character of the base takes place ; 

 clay slate containing distinct fragments of the same sub- 

 stance beginning to prevail, and alternating with distinct 

 beds, or rather portions of beds, of the same rock in 

 a simple state. The base then gradually becomes more 

 calcareous, and is found to consist of minute fragments 

 of slate and limestone ; while the fragments of granite and 

 quartz at length disappearing, those of limestone alone 

 remain. Thus there is at last perfected a series of beds 

 of considerable thickness, formed of a calcareous breccia 

 having a compound base of schist and limestone, and con- 

 taining imbedded fragments of the latter substance. 



The analogy of this breccia, and indeed of the whole 

 series, to those which occur in the secondary strata, is 

 very apparent. Substituting sandstone, shale, and se- 

 condary limestone, for the three simple rocks above 

 described, a sequence will be seen to exist among these 

 primary strata, similar to that which occurs among the 

 secondary. This is one, among many other examples, 

 showing the great analogy between the primary and the 

 secondary rocks : similar instances are pointed out in 

 different parts of this work. 



At length the breccia gradually disappears, and is suc- 

 ceeded by a continuous and compact limestone, of a gra- 

 nular texture and of great hardness. Its predominant 

 colour is an ochrey or reddish white, occasionally mottled 

 with grey and brown, and veined with dark red. These beds 

 continue to the end, so as to terminate the whole series 

 to the westward ; forming the high cliffs already described. 

 It is therefore impossible to conjecture what rocks follow 

 in the order of succession downwards ; as neither island 

 nor rock intervenes between these and the southern coast 

 of Mull, which has been already shown to consist of 

 secondary strata surmounted by trap. I shall here there- 

 fore terminate the account of these strata, referring, for 



