In writing my little paper on vein-quartz I was particularly anxious not to introduce controversial matter, but to be strictly orthodox throughout. After the paper was published I was much perturbed to find that I had unwittingly come into collision with two incidental remarks in General McMahon's most interesting paper on the Satlej granite, which was the subject of his address to Section C at Belfast. My oversight arose owing to the said remarks being incidental, and no stress having been laid upon their paramount importance.