It seems to be one of the chief objects of the British Association for the Advancement of Science in changing the place of meeting every year, to bring more prominently before the members of its respective sections such points of interest in their own department of Science as are afforded by the various localities. In accordance with this principle, I beg to lay before you some observations concerning the geology of a district not more distant than about two hours' railway journey from Dublin, which will, I trust, be of peculiar interest on the present occasion. The district I refer to is the hill country north of Dundalk, of which Slieve Gullion forms the most prominent feature. This mountain is a somewhat isolated mass, attaining an elevation of about 1900 feet, and is situated to the north-west of the hilly and picturesque country lying between the bays of Dundalk and Carlingford, or due west of the more remarkable group of the Mourne Mountains.