Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/132



From its southern boundary it emits two water courses; the Mayowla which takes an eastern direction and flows into Lough Neagh; and the Moyle which passes to the west and joins the Strabane river.

On the north the Fanghan waters a beautiful valley, at length discharging itself into Lough Poyle.

Sawell is the highest point of this group: Dr. Berger has fixed its altitude at 2257 feet above the sea. The whole of this extensive and lofty tract is primitive to the very front towards Lough Foyle. Mica slate is the predominating rock, constituting exclusively almost nine-tenths of the district: it is accompanied by primitive limestone in the lower part of the country.

On the eastern bank of the Roe this system of mountains is succeeded by a range of secondary heights, covered by an enormous platform of basalt and forming a part of that system which will in the next place be described. These secondary masses repose upon and conceal the mica slate in the eastern part of Derry, but the mica slate again emerges from beneath this covering, after an interval of near 30 miles, in the N.E. of Antrim, and swells into mountains which break down abruptly towards the coast between Tor Point and Cushenden bay.

The exact correspondence in structure of the opposite points of Ireland and Scotland here again demands our observation; the Mull of Cantire which faces Tor Point resuming the chain of mica slate which was there broken off. The Cantire hills are connected with the Grampians, a chain strikingly similar to that which has been above described in all the circumstances of its composition; and it may be added, as compleating this analogy, that the mica slate of Ireland is succeeded on the south (where the Antrim coast exhibits it in section) by a conglomerate, perfectly resembling that which is so well known as skirting the Grampians on their southern border.