A Portion of the district referred to in this paper was described by me in a communication to the Geological Society, on May 22nd, 1878, and this was afterwards published in the Quart. Journ. Geol. Soc. vol. xxxiv. In that paper, however, many of the facts which had led me to the conclusions stated therein had to be omitted, and the important evidence derived from the microscopical examination of the rocks was hardly touched upon. It was then intended that this evidence should be given in an appendix to the paper, but, unfortunately, circumstances at the time prevented it.