Feathersioiiliaugh^ s Geological Report. 



71 



nean origin, whilst the hydrates or ferruginous ores of the 

 superior beds are to be considered generally as oxydes de- 

 rived from them. Many of the ferruginous sand rocks were 

 doubtless once in the state of our recent bog ores, just as 

 many conglomerates and great rocks were once in the state 

 of loose gravel. The compact metals, with the exception of 

 the sulphurets of lead and zinc, have their principal seat in 

 the primary beds, either in veins which traverse mineral 

 masses, or disseminated in these last. These veins may have 

 either mineral or metallic matter, or both, in them. They are 

 vertical, inclined, and horizontal, often running in parallel 

 courses as if they had a contemporaneous origin, and intersect- 

 ing each other in such various ways as to leave no doubt that 

 many of the intersected ones have been formed prior to those 

 by which they are intersected. There is a very instructive 

 exhibition of this kind at Fudia, one of the Western islands.* 

 In diagram No. 8 is a representation of different kinds of 

 mineral veins intersecting the gneiss, and of the dislocations 

 which have taken place during the injection of some of these 

 veins. It will be observed that the striped laminiB of the gneiss, 

 produced by the plates of mica, which once were continuous, 

 have their continuity interrupted, as if they had been violently 

 separated, and one portion shifted higher up, or depressed 

 below the natural level. To the left is a vein of granite in- 

 tersecting the gneiss, and itself intersected and shifted by a 

 vein of quartz. At the top is another vein of granite inter- 

 secting the gneiss, and again intersected by a vein of trap. 

 It is to be inferred from these appearances, that the veins of 

 granite, and perhaps the trap vein, had penetrated the gneiss 

 before it had taken its indurated state, and that, posterior to 

 its induration, a dislocation or shifting took place, occasioning 

 the fissure filled by the vein of quartz. The dislocations of 

 strata occasioned by the exertion of such intense subterra- 



* McCulloch's Western Islands. 



