Mineralogy of Sky. 185 



compound of that substance and augit in minute admixture, and 

 not a greenstone ; a term which has been too indiscriminately 

 lavished on many of the obscurer members of the trap family. 



The last circumstance respecting trap which requires correction 

 is the account of a vein passing through the marble quarry in 

 Strath, and supposed to terminate in a mass of syenite. I did not 

 in the original paper lay much stress on the conclusions which 

 might be drawn from it, but I can now however say that no in- 

 stance has occurred to me in Sky of a trap vein being cut off by 

 the syenite. The half opened state of the quarry at the time I saw 

 it, and the rubbish with which it was encumbered, misled me into 

 the report which I gave ; a report which a moment's view of its 

 present exposed state was sufficient to rectify. The trap veins (for 

 there are two,) enter it on one side together, appearing at first like 

 one ; and being cut deeply through on that side of the excavation, 

 while they were not to be seen on the other, I readily concluded 

 them to be terminated. By a very singular coincidence they diverge 

 from each other immediately at the place of entrance, branching 

 away in an angle greater than a right one, and in this interval the 

 excavation was effected, without exposing the separated veins, 

 which I afterwards traced through the soil on the opposite side, 

 after the rubbish was in some measure removed. The remainder 

 of the error consisted in mistaking an irregular lump of a very 

 anomalous kind of sandstone which is entangled among the marble 

 and the trap veins now described, for the syenite which is in the 

 immediate vicinity similarly interfering with the limestone, and of 

 which, pieces detached by the workmen were lying upon this sand- 

 stone as if they had been recently separated from it. If care and 

 caution are required in examining- the most simple appearances 

 among the regular rocks, a tenfold portion is necessary when we 



