Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/208

 the frustum of an enormous cone of great height and comparatively narrow base.

Both Cruach-a-Crue and Lurgethan present thick basaltic masses on their summits, resting at considerable elevations on strata of chalk; in the former mountain the lower beds are concealed by grassy slopes, in the latter red sandstone is exhibited in several points towards its central region: here probably a more full examination might detect and ascertain the thickness of the green sand and lias, which from the general structure of the district might be expected to intervene between the chalk and red sand; the spot certainly appears very favorable for such an enquiry.

At the foot of Lurgethan the coast presents two low cliffs divided by a valley which affords a passage towards the sea to a small rivulet; these cliffs are composed of red sandstone and a conglomerate containing rounded fragments of quartz, the rock being altogether similar to that which Dr. Berger has described as the old red sandstone in the neighbouring hill on which Cushendon church is built: since, between these cliffs and the sections visible in the precipices which occur near the summit of Lurgethan, a considerable space intervenes through which the substrata are concealed by grassy or cultivated slopes, it is not easy to determine the geological relations existing between the sandstone in the higher region and that on the level of the sea.

On the most southern of these cliffs near the strand at the mouth of the Glenarif river stand the remains of an old fortification known by the name of Red bay Castle; close to this spot several basaltic dykes traverse the conglomerate, one of these, remarkable for its great thickness, having resisted the action of the waves which have encroached considerably on the adjacent cliffs, presents some bold detached crags projecting from the beach. The conglomerate forming