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 instance has occurred to me in Sky of a trap vein being cut of 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 sandstone 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
