Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/145

 formation (principally chalk and basalt) occur towards the summits of the hills, capping the primitive rock.

The valley of Glendun is formed exclusively of mica slate as far as Done, a village more than five miles inland, here the secondary deposits commence, at the elevation of 590 feet above the sea.

From the mouth of the Glendun river the mica slate extends along the coast, in a northerly direction, as far Murlock Bay, near Fairhead, a distance of about seven English miles: it is here associated with a few other primitive rocks, hereafter to be described. The local name of Cushleak is given to this part of the coast.

Vestiges of mica slate occur on the road from Cushendon to Ballycastle. I have seen it in situ at Ballyvarleys in the bed of a rivulet, skirting the base of Knocklead on the north-east, and have traced it in several other points on the slope of that mountain, particularly at Kileseg, and the low Market hill near Ballycastle. Passing into the county of Londonderry, that great and central mass of mica slate, which from the parallel of the Mayowla river reaches Lough Foyle, extending to the east and west between the Roe and the Moyle, claims our principal attention; it may be computed to cover a surface of at least 476 square English miles of mountainous ground, over which several distinct summits are scattered, including the following, of which I have determined the elevation:—Sawell 2257; Feen Glen 2097; Mullaghash 1677; Moneynieny 1477; Sphell Covagh 1867; and Dunlogan mountain 1467 feet.

The river Roe, from the neighbourhood of Newtown Limavaddy to its source, may be assigned as the general line of demarcation between this primitive group and the red sandstone which forms the base of the secondary mountains of the third system, (see Introduction): the mica slate is however occasionally seen on both