1866.] . MACFARLANE — ON CUPRIFEROUS BEDS. 9 



dark coloured portion consisted probably in greater part of 

 mica, and to judge from the comparatively low specific gravity of 

 the rock, little or no pyroxene or hornblende could be present. 

 The mineralogical composition of this trap is therefore probably 

 as follows : 



Delessite 40 



Mica 20 



Labradorite 40 



100 

 The ' Fluckan ' which underlies the trap last described is sepa- 

 rated from it by a small seam of clay. The fluckan itself is 

 a fine grained, dark-red shaly rock in which pieces of a greenish 

 blue colour are sometimes seen. Both substances are fusible 

 before the blow-pipe and contain occasionally small grains and 

 flakes of copper. It resembles the old Thonstein (claystone) of 

 the Germans, now more properly named Felsite tuff. 



The conglomerate upon which the foregoing rock rests, has 

 acquired some celebrity on account of its being mined for copper 

 on the property of the Albany and Boston Mining Company. The 

 boulders and pebbles consist of various species of porphyry. One 

 of them has a dark brown matrix with small white crystals of 

 feldspar j another has a matrix of the same colour but with larger 

 crystals of orthoclase, while a third variety consists principally of a 

 fine grained mass of orthoclase with which a small quantity of a 

 dark coloured mineral occurs in particles too small for determina- 

 tion. The matrix consists of a coarse grained sand of porphyritic 

 material, impregnated with calcareous matter. In many places the 

 interstices are not at all filled up, in others calcspar is the matrix, 

 and very often in the lower part of the bed the matrix is almost 

 pure metallic copper. Sometimes the metal completely fills the 

 whole space between the pebbles, sometimes it is accompanied by 

 calcspar, but much more frequently it is disseminated in fine par- 

 ticles through the coarse grained matrix. Sometimes a pebble is 

 found quite saturated with copper, but it seems to have been of a 

 more porous nature than the others and an amygdaloidal structure 

 may be detected in it. 



As above mentioned, a bed of sandstone underlies the conglo- 

 merate. It shews traces of stratification, is of a dark-red colour, 

 and evidently consists of the same material as the conglomerate 

 pebbles but in finer particles. 



