1865.] MACFARLANE — GEOLOGICAL SKETCH OF ROSSIE. 271 



was again found out-cropping, and from this point to beyond John 

 Robb's house it was traced uninterruptedly. About half way be- 

 tween the latter place and the spot where the rock was first found, 

 the strike changes to N. 22 East, which direction it maintained 

 to the southward as far as it was followed. This fahlband was 

 therefore actually traced for a distance of about a mile, but it 

 doubtless extended much further. I have in the paper already 

 referred to (Canadian Naturalist, vol. vii, p. 7) given a minute de- 

 scription of these rocks and the ore-deposits which occur in con- 

 nection with them in Norway, but it may be advantageous here to 

 recapitulate their general characters. A fahlband (the first sylla- 

 ble being most probably derived from the German word fahl or f aid, 

 rotten) is a zone of rock occurring in the Primitive Gneiss formation 

 varying from a few to several hundred feet in thickness, having a 

 length on the strike of several miles, and possessing the same dip 

 and strike as the rocks adjoining it, but distinguished from them 

 by the decomposed appearance and reddish-brown color which it 

 assumes on exposure to the atmosphere. This peculiar brown 

 weathering is caused by the oxidation of the magnetic and iron 

 pyrites with which the rock is impregnated, the ferric oxide result- 

 ing from their decomposition being the coloring substance. The 

 quantity of these sulphurets of iron necessary to produce this effect 

 is often exceedingly small; and indeed it is sometimes scarcely pos- 

 sible to distinguish them even in the freshly broken and undecom- 

 posed rock, so finely disseminated are they through it. By the 

 help of the magnifying glass they can, however, always be detected 

 in any part of the rock which exhibits the reddish-brown surface 

 above mentioned. The impregnation is altogether independent of 

 the nature of the rock ; gneiss, mica-schist, and hornblende-schist 

 being alike found constituting fahlbands. Their course is often 

 marked by depressions in the rocks, caused probably by their 

 greater proneness to decomposition. Almost all the mines of any 

 importance in the south of Norway, with the exception of those of 

 iron, occur on bands having the characters above described. Sil- 

 ver, cobalt, nickel, and copper have all been found in very remune- 

 rative quantities within this peculiar rock, either in veins crossing 

 the band (silver) or disseminated through it more or less plentiful- 

 ly in fine grains (cobalt), or in irregular masses sometimes rudely 

 parallel with the strike (copper, nickel). 



The band of red-weathering rock above described as occurring 

 to the south-west of Eossiehas all the characters of afahlband. The 



