Kinahan — On Granite and Metamorphic Mocks. 243 



Eocene Whinstones (Basalt and Doleryte), the western margin of 

 the great sheets of these rocks, which occupy the greater part of 

 the Co. Antrim. 



Associated with these, to the northward, in the vicinity of 

 Portrush are granite roots (granitone, or highly crystalline diorite) ; 

 and in other places, as near Croagh, to the south, are conglomerates 

 and other tuffs. In the Croagh neighbourhood there seem to have 

 been one of the volcanic vents, from which the sheets were poured 

 out. 



The granitone occurs in the Skerries, off Portrush, and in 

 Portrush Head, where it was extensively quarried for use in the 

 Harbour Works. 



In the Basalt region, the harder varieties of doleryte and the 

 clinkstone (the local name for the fine basalt that has a metallic ring), 

 are the materials generally used for ordinary building purposes. 

 They can be raised in large well-shaped blocks, and scapple 

 freely. Some, especially the clinkstones, polish well, and are very 

 similar to, if not identical with those used in some of the monuments 

 and statues of the ancient Egyptians and Romans. 



The abutments and piers of Coleraine Bridge are built of these 

 stones ; they have also been used in Honeyrnore for quoins and 

 string-courses, the facings being of the white limestone, as also 

 in numerous other towns, and the country-houses in the area, 

 sometimes only for quoins and dressings, but sometimes, also, for 

 facings and rubble work. In the basalt region the quoins and 

 dressings are sometimes of the white limestone, while the facings 

 are basalt. 



TYRONE. 



In the east of the county, coming in from the counties of 

 Antrim and Londonderry, is a small portion of the Ulster Tertiary 

 Basalts and Dolerytes, while the northern part of the county is 

 composed of metamorphic rocks, probably equivalents of the Ordo- 

 rician and Arenig or Cambrian, the latter being much more altered 

 than the former. Associated with these are metamorphosed igneous 

 rocks with veins, dykes, and other intrudes of granitic and other 

 newer exotic rocks. The Arenig (?) schists, especially their 

 associated metamorphosed exotic rocks, seem worthy of notice. 



