262 ACCOUNT OF THE MINERALOGY 



Like all other trap countries, the Faroe islands are intersec- 

 ted by innumerable dykes. Those we examined were princi- 

 pally of fine-grained greenstone, and more or less formed of 

 prismatic distinct concretions. They frequently occur in the 

 hollows, between hills, and in gulleys which intersect the 

 precipices, being, from their proneness to decompose, them- 

 selves the cause of these indentations. They do not appear to 

 have any peculiar direction, although they be generally very 

 nearly perpendicular. Many we perceived cutting the hills 

 from top to bottom. Some we could trace from one island 

 to another ; and even where covered with soil, we often ob- 

 served their track, by the superiority of the verdure on the 

 surface ; the dyke, from its looseness of texture, having 

 acted as a drain, and rendered the bottom more nourishing to 

 the vegetable root. This circumstance proves how permeable 

 these dykes are to moisture, and helps to account for the sin- 

 gular fissures that often present themselves on the shore. 

 They are considered by Landt as marks of some violent con- 

 vulsion in nature ; and to a common observer, they have very 

 much that appearance*. The effects of the weather, however,, 

 without any such assistance* are quite sufficient to accomplish 

 this end ; nor will its operations be tardy ; the constant ac- 

 tion of the surface-water on the summit, and the continued 

 lashing of the waves at the base, are agents of sufficient power ; 

 and we have thus dykes washed from their sockets, for an ex- 

 tent of several hundred feet, leaving a frightful chasm in rocks 

 of enormous height. 



Two of the most singular dvkes we met with, are between 

 Thiornivig and Westmanhavn, on the north-west coast of Stro- 

 moe. The first intersects a mural precipice, a little be- 

 yond Stakken. This is a double dyke : immediately under 

 the edge of the clifE, it divides, and shortly after joins again j 



it 



