Mineralogy of Sky, $9 



most rare, and on no occasion have I seen barytes, a substance not 

 uncommon in the trap amygdalolds of other places. At TaUsker, mica 

 is to be observed in some varieties, a substance among the least 

 common ; and in the vicinity of Scavig, epidote is an ingredient, 

 the rock resembling precisely the specimens found in Caer Caradoc. 

 I have never met with olivin in these traps. 



Various complexions of greenstone are found among the strata in 

 different parts of the island ; but they are far less common than the 

 basaltic varieties. In one instance I observed specimens in which the 

 crystallization of the hornblende was very perfect. The porphyries 

 of this kind occur also in different places, but like the greenstones 

 they are much inferior in quantity to the uniformly basaltic kinds. 

 The felspar Is sometimes glassy, sometimes opake, and the com- 

 pound at times forms beautiful specimens. I did not observe among 

 the stratified trap any example of clinkstone ; and wacke is I believe 

 totally unknown in this island, although some of the more earthy 

 amygdalolds have been improperly designated by this term. 



The substance known by the name of trap tuff, and which I have 

 for reasons elsewhere assigned called trap conglomerate, is the last 

 which I shall enumerate of the varieties which come under the ge- 

 neral denomination of trap, and indeed no more can be enumerated, 

 since the terms applied to the several members of this family are 

 exhausted. This also occurs every where, and (as is I believe very 

 common) every where irregularly intermixed with the other va- 

 rieties. I saw no example however of that variety coatalning 

 rounded nodules and foreign substances which occurs in Canna, the 

 conglomerate in Sky always appearing to form a loose mass of angu- 

 lar fragments of gravel and sand easily mouldering to dust and soil. 



It is now necessary to describe some substances which although 

 not appertaining to this family are often found united with it, and 



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