Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/67

 most rare, and on no occasion have I seen barytes, a substance not uncommon in the trap amygdaloids of other places. At Talisker, 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 compound 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 amygdaloids 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 general 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 varieties. I saw no example however of that variety containing rounded nodules and foreign substances which occurs in Canna, the conglomerate in Sky always appearing to form a loose mass of angular 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