ICXD Guide to Belfast. 



stand out as clear bright blebs against the dull ground mass 

 in a hand specimen. 



The age of the rock is not definitely determined, but from 

 the fact that numerous well-rounded and worn fragments of it 

 are found in the Old Red Sandstone to the north, it is evident 

 that it is earlier than the conglomerates of Cushendun. 



CUSHENDUN. 



Another exposure of acid rock is found to the north-east 

 of Cushendun, and in sections exposed along the road 

 above Tornamoney Point. The base in this case is fine- 

 grained granitic, with numerous large crystals of felspars, 

 which in hand specimens often show the crystal forms in 

 perfection. In micro-sections the orthoclase crystals are 

 found to be beautifully zoned, and the rock contains well- 

 defined crystals of plagioclase. Biotite also occurs, some- 

 times altered to a green chlorite. 



The eurite of Cushendun has been found very frequently 

 in the boulder clays to the south of the district, and from its 

 widespread distribution as an erratic, it is evident that the 

 exposures of this rock must have been of considerable extent. 

 /;/ situ the rock occurs among the crystalline schists, and 

 may be considered the plutonic representative of the quartz 

 porphyry of Cushendall. 



The Lamprophyres of the Dlstrict. 



Dyke rocks belonging to this group of igneous intrusions 

 are especially numerous in County Down. The Ards. 

 peninsula on the east of County Down contains several 

 hundred dykes belonging to the Lamprophyre group, and 

 similar dykes occur, but less frequently, in the inland area. 

 The dykes occur for the most part along the bedding planes 

 of the steeply tilted Silurian sediments, and only in relatively 

 few instances are seen to cut across these rocks. This mode 

 of occurrence renders their recognition in the field a matter 

 of some difficulty, as the dykes very closely resemble the 

 harder grit bands associated with the Silurian shales. This 

 is especially the case in the south of the peninsula, but in 

 the more northern examples the dykes weaiher less readily 

 than the sediments, and thus stand out boldly above the 



