OF THE FAROE ISLANDS. 257 



opposite in geology, a description of them belongs more pro- 

 perly to this part of my subject. 



From the proofs we met with in Faroe, of the igneous ori- 

 gin of trap rocks, I think it almost unnecessary to enter into 

 any discussion respecting the formation of Calcedony, as no 

 doubt can very reasonably be entertained of its co-existing with 

 the matrix in which it is inclosed. The laws by which it 

 has been regulated, in assuming the various appearances it now 

 presents, are, however, beyond our reach ; nothing I met with • 

 tended in any degree to elucidate the subject. 



Calcedony occurs in the rock in the most irregular masses, 

 generally rounded, and sometimes shooting into forms like 

 bunches of grapes. It is either solid, or in hollow cavi- 

 ties, and varies in size from the head of a pin to a foot or up- 

 wards in diameter. When solid, the masses are marked with 

 parallel lines, straight or concentric, sometimes with both/; the 

 latter forming a border or coating round the straight lines. 

 The solid pieces are frequently penetrated by minute stalac- 

 tites of the same substance, branching through the mass, in a 

 form perfectly vegetable ; and as these always contain a por- 

 tion of green earth, it occasions an appearance extremely 

 similar to moss; which no doubt has given rise to the 

 assertion of Landt, that moss and straw actually occur 

 in them. I have sometimes found, on breaking the solid 

 masses, which contained these slender fibres, the latter would 

 separate from their bed, and leave an impression of their form, — 

 a tolerable proof that they must have been in a solid state pre- 

 vious to their being enveloped in the larger mass. I have ob- 

 tained very few stalactites, whose centres are not occupied by 

 this green substance; it seldom exceeds in thickness the 

 twentieth part of an inch, and varies in colour, from a very 



Vol. VII. K k dark 



