280 GIGHA AND CARA. GEOLOGY. 



ranked, for want of other names, under the leading titles 

 of quartz rock, micaceous schist, hornblende schist, and 

 chlorite schist ; although the two latter often deviate 

 considerably from the definitions. 



There is nothing in the quartz rock or micaceous schist 

 to call for particular notice. They are both extremely 

 distinct in character, and the beds are of considerable 

 thickness. The unequal action of the sea on these rocks 

 where they occur on the shore, renders both of them 

 conspicuous at a distance. The chlorite schist occurs 

 under many distinct forms, but the most prevalent is 

 fissile and scaly in texture ; being often so regularly 

 laminar as to admit of being used for slates. The other 

 varieties will be better deferred till the whole series shall 

 be collectively considered. The hornblende schist pre- 

 sents also many varieties, the consideration of which must 

 be in the same manner deferred, but the prevalent beds 

 consist of felspar and hornblende ; scarcely schistose, and 

 often resembling the greenstones of the trap family. 



It is reported that copper has been found in Gigha ; but 

 on this subject I could procure nothing but hearsay and 

 vague testimony, while there is reason to believe that 

 pyrites, which occurs in many of the rocks, has been mis- 

 taken for it. 



Common chlorite is found imbedded in the quartz veins 

 which traverse the chlorite schist, as is usual wherever 

 these rocks are found. Large concretions of green com- 

 pact felspar are also to be seen in different parts both 

 of the hornblende and of the chlorite schists. 



Trap veins are to be observed traversing the island in 

 various directions, but no where possessed of any pecu- 

 liarities to render them objects of notice, after the nu- 

 merous examples which have fallen under review in de- 

 scribing the other islands. 



It was remarked at the beginning of this account that 

 there was a general resemblance between Gigha and the 

 accompanying island Cara, and they may indeed be con- 



