291 



varies from 170 to 312, or say it is 250 feet average. This makes a 

 difference of 1250 feet that the Slieve Gallion chalk was elevated above 

 that in the Magherafelt plateau. 



From the east side, this patch, about half a square mile, appears 

 decidedly to have been elevated ; yet the aspect from the north-west 

 side cannot be forgotten — that is, the very regular elevation of the 

 chalk in Derry from the sea at Magilligan along the western escarp- 

 ment by Keady, Donald's Hill, Benbradagh, and Craig na shoke, to 

 Slieve Gallion, ascending regularly all the way from sea level to the 

 highest chalk in the two counties. From the western country this band 

 does not appear in an unnatural position, but looks like the southern 

 continuation of the ascending zone. This seems still the more natural, 

 that the Sperrin Mountains of mica slate branch off westward at the 

 same high level, south of Dungiven. 



That the Slieve Gallion mountain, however, on which this patch of 

 chalk rests, has been itself elevated from a lower level, most probably 

 that of the Magherafelt plateau, as just stated, is shown by the follow- 

 ing arguments : — It is situated between the valley of Ballinascreen, 

 which is low ground, on the north, and the low ground about Cooks- 

 town, on the south. It forms the eastern and highest part of a ridge, 

 composed of granite, greenstone, and metamorphic rocks, which ridge 

 trends away south-west from this point, by Beleevnamore, Creggancon- 

 roe, and Termonmaguirk, to near Omagh. This ridge, so formed, of 

 crystalline and metamorphic rocks, being quite distinct from the mica 

 slate of the Sperrin Mountains, appears to have undergone a movement 

 in itself, and to have been protruded, thus accounting for the elevation 

 of Slieve Gallion, with its patch of chalk upon its back, independently 

 of its proximity to the Sperrin or any other mountains. In each of 

 those cases described the chalk is covered by the trap of the country. 

 Those differences of level proclaim, that the movements which produced 

 them took place subsequently to the deposition of the chalk and the 

 eruption of the trap. 



Porphyet. 



The porphyry of Cushendall occupies a comparatively small district. 

 It appears to have been connected in some way with the elevation of 

 Lurgethan Mountain ; and, if so, it is newer than the new red sand- 

 stone, with which it is in contact at Bellisk, and the chalk, and perhaps 

 newer than the trap itself that caps that mountain ; for it will be seen 

 in the Table that the chalk in the north end of the mountain stands at 

 about 940 feet high, while the same zone in Glenariff is under 100 

 feet at the east side of the river at Barnahilly bridge. 



The little district surrounds the village of Cushendall. It is bounded 

 on the east by the sea, and occupies the shore for half a mile, between 

 the mouth of Cushendall Eiver and the Coast Guard station at Bellisk. 

 On the north and west the boundary forms a curve, convex to the north- 

 west, beginning at the mouth of the Eiver Dall, passes 100 yards north 

 j of the schoolhouse, through the villages of Carnahagh and Tully, and 



