ULVA, c. MINERALS; 



It contains, as far as I could perceive, but one variety 

 of amorphous trap, disposed, as is the universal rule 

 along this coast, in irregular terraces. 



All these islands, as well as the numerous and nameless 

 rocks that skirt these shores, are covered with verdure, 

 and tenanted by sheep or black cattle : even the rock 

 which can maintain but one lamb is not unoccupied. 



Having, in the account of Sky, made some remarks 

 on the transitions of nadelstein into quartz, it will not 

 be superfluous here to notice a similar transition between 

 analcime and that substance. The analcime of Ulva 

 however resembles that of Sky and of Mull, and rarely 

 presents any decided transitions of this nature. Where 

 they do occur, they are easily discovered by the different 

 action which acids exert on the several varieties ; and 

 the variations of character not unfrequent in this mineral, 

 will be found, on a more complete analysis, to depend 

 on the various proportions of silica in its composition. 

 The most remarkable examples of these varieties occur 

 in the Kilpatrick hills in Dumbartonshire. Here, as I 

 shall have occasion hereafter to describe more particularly, 

 the analcime passes into prehnite. At the same time 

 it passes by an uninterrupted transition into quartz ; the 

 crystal of the one substance being sometimes perfect 

 at one side of a specimen, and the other presenting an ex- 

 ample of common quartz. In one case in my possession 

 the latter possesses the form of its primitive rhomb. From 

 this it is easy to account for the differences above men- 

 tioned which analcime presents when exposed to the 

 action of acids, and for the different proportions of 

 the several earths which it is found to yield on ana- 

 lysis. Hence also the differences of fracture which 

 it displays, and the impossibility, in many Ceases, of 

 procuring a definite fragment. It is an important cir- 

 cumstance to remark, that throughout this great range 

 of composition, the crystals continue to maintain the same 

 form ; a fact however which corresponds with others of 



