OF THE FAROE ISLANDS. 259 



and polished, a radiation of fibres may be observed diverging 

 from the slender green thread which occupies the centre. 



It does not appear as if the form of the stalactites were ow- 

 ing to the pendulous position in which thej are found, as they 

 sometimes occur attached by the side,- and terminated both 

 above and below. With respect to size, they vary, from the 

 thickness of a hair to two inches in diameter ; but I have not 

 found any above four inches in length. 



The cavities are often entirely lined with crystallized quartz, 

 which always forms a distinct coat, and is sometimes interpo- 

 sed between the two coats of calcedony. To illustrate these 

 combinations, I selected a series of specimens, all of them por- 

 tions of hollow masses. In the first, the quartz is transparent and 

 crystallized, in the usual form. In the second, the crystals are 

 coated with calcedony, but so slightly, that the shape of the 

 quartz is preserved entire. In the third, the edges of the crystals 

 are rounded off. In the fourth, the apices are partly converted 

 into mamillons. And, in the fifth, the crystallization is entirely 

 replaced by a mamiliated surface ; the quartz being, visible 

 only in the section of the mass. Nearly the whole of these 

 changes may be traced in one specimen belonging to Sir 

 George Mackenzie. At one part, the crystallization is nearly 

 complete, while, at the other extremity, it is perfectly mamil- 

 iated. I never observed quartz crystals among stalactites, 

 or stalactites among crystals. The quartz and calcedony al- 

 ways occur in distinct coats, one or other occupying the whole 

 surface, and, except very rarely, with perfect uniformity. 



Quartz and calcedony is a combination well known to mi- 

 neralogists ; but before visiting Faroe, I was not aware, that 

 the latter substance occurred, also intimately connected with 

 zeolite. Some Danish mineralogists have considered this sub- 

 stance as the connecting link between calcedony and opal ; a 



Kk 2 conclusion 



