I n a paper communicated to the Geological Society, and published in the 30th volume of the ‘Quarterly Journal,’ I briefly described the microscopical structure and composition of the various masses of igneous rocks which occur in the Carboniferous strata of the Midland Counties, with the exception of those found in the Warwickshire Coal-field. I now propose to complete the series with a short account of the only hornblendic rocks to be found among them. Although they form but a small group they are of considerable interest, as some of them present remarkable varieties of structure, and others a mineral constitution which distinguishes them from any British rocks hitherto examined. The geology of the Warwickshire Coal-field has been described in the Memoir of the Survey published in explanation of sheet lxiii. S.W. ; and a reference to that map will show that the rocks now to be described are restricted to the district between Atherstone and the village of Marston Jabet, about two miles south of Nuneaton, and also that the several bands and larger masses occur only in the lower unproductive beds of the Coal-measures and in the underlying Millstone Grit. Although the sheets usually run very regularly between the beds of shale they are clearly intrusive, as they sometimes pass from lower to higher beds, and have invariably altered the shales in contact with their upper and under surfaces. The junction of the eruptive and sedimentary rocks may be seen in several clear sections. In a quarry in Purley