. Geological magazine. believe it, however, to be always a member of the pyroxenicgroup, Aiz. some variety of augite, hornblende, or enstatite. In conclusion, may I add that Mr. Teall appears to have slightlymisunderstood the drift of my remark quoted by Colonel or not there is evidence of mechanical action on the serpentineat Porthalla is hardly germane to the question. Of course I shouldsay that to assign the banded structure in this rock to pressure is atpresent just as much an hypothesis as it is in regard to the bandedgabbro. But, apart from this, the difficulty, which I h
. Geological magazine. believe it, however, to be always a member of the pyroxenicgroup, Aiz. some variety of augite, hornblende, or enstatite. In conclusion, may I add that Mr. Teall appears to have slightlymisunderstood the drift of my remark quoted by Colonel or not there is evidence of mechanical action on the serpentineat Porthalla is hardly germane to the question. Of course I shouldsay that to assign the banded structure in this rock to pressure is atpresent just as much an hypothesis as it is in regard to the bandedgabbro. But, apart from this, the difficulty, which I had felt and towhich Colonel McMahon referred, was this—that, when the gabbrois so remarkably banded, then the serpentine shows little or no signof mechanical disturbance. Porthalla is some miles from bothKarakclews and the Landewednack district, and, so far as I know,gabbro does not occur in association with serpentine either there ornear Mullion Cove. T. G. Bonney. Geol. Mag. 1887. Decade III. Vol. IV. Pl. VI.
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