of the North of Irelatid. 137 



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 secon- 

 dary 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 asso- 

 ciated 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 Bally- 

 castle. Ihave 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 ; Money nieny 1477 ; 

 Sphell Covagh 1867; and Dunlogan mountain 1467. 



The river Roe, from the neighbourhood of Newtown Limavaddy 

 tx) 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 In- 

 troduction) : the mica slate is however occasionally seen on both 



Vol. II.. s 



