SHUNA. GEOLOGY. 



These alternate in frequent and thin strata, almost always 

 very decided and without gradation, and are most easily 

 examined on the southern and eastern shores. 



The characters of the micaceous schist vary. At times 

 it presents the most ordinary aspect, being a foliated mix- 

 ture of mica and quartz. In other cases it is finely 

 laminar and silky, consisting almost entirely of the former 

 mineral. 



The quartz rock is sometimes of a peculiar character ; 

 being of a buff colour, and, though extremely crystalline 

 and compact, marked by a concretionary structure ; while, 

 from its great toughness, and the peculiarity of its frac- 

 ture, it appears to contain felspar in intimate union with 

 the quartz. 



Among these predominant strata there occur several 

 varieties or modifications of chlorite schist, some being 

 of an unusual aspect ; besides which, occasional beds 

 of hornblende schist are also found alternating in an irre- 

 gular manner with the other substances. It would not 

 be easy at the present period of this investigation, to 

 convey an adequate idea of the nature and connexions of 

 this series ; and as it occurs towards the south, under a 

 much more interesting form, and through a much larger 

 tract of country, it is preferable to defer the subject to a 

 future period. 



At each end of the island, a bed of dark blue crystalline 

 limestone is seen among these strata ; and it is wrought 

 for economical purposes. The state of the intermediate 

 ground does not admit of the continuity of these two 

 rocks being traced ; but from the general bearing of the 

 strata it is possible that they are parts of the same bed. 

 That does not however necessarily follow, as, in this 

 schistose series, limestone is of frequent occurrence, and is 

 generally found to occupy a very limited range ; the beds, 

 after a short progress, being extenuated to nothing. 



It is perhaps almost superfluous to add to this cursory, 

 but sufficient, description, that trap veins occur in thf 



