Igiu'ous Rocks. 99 



"The rhyolites of the County Antrim are as a rule poor in 

 ferromagnesian constituents, but the occurrence of these 

 minerals divides the rocks into two groups, the biotite 

 rhyolites, such as those at Templepatrick, Kirkinriola, and 

 Hallycloughan, and the augite rhyolites, represented on 

 Carneariiey and Sandy Braes. All the types, whatever their 

 structure, are fairly rich in porphyritic constituents, with the 

 exception of the fluidal rhyolite of Cloughwater." 



The only section from which evidence may be directly 

 observed is the quarry at Templepatrick. In this the 

 rhyolite is intrusive between a mass of basalt and Chalk; 

 but it is insufficient to give us data for determining the 

 exact age and nature of the flow. In many of the beds, 

 between the upper and lower basalts, rounded and travelled 

 pebbles of rhyolite are found, notably at Glenarm and Bally- 

 pallidy. These intermediate beds — containing iron ore, 

 l)auxite, and plant remains — at Ballypallidy represent a con- 

 siderable interval of time, during which the rhyolite came to 

 be exposed at the surface, either by a direct extrusion of 

 volcanic material in this interval, or by laying bare by denuda- 

 tion of some intrusive masses of Lower Basalt age. 



The exposures of rhyolite occurring close on a line with 

 north-west and south-east trend, might lead one to imagine 

 that ihey were all connected with one fissure system, and that 

 they are at least bosses or small laccolites at points of 

 weakness: but the variety of the material found within easy 

 range of Tardree would seem to indicate that this hill is the 

 denuded core or plug in a vent, the materials from which 

 found their way as a lava-flow over the surrounding district. 



Thk Quartz Felsite of Cushendall. 



This rock is found chiefly in the area south of Cushendall. 

 Many exposures are seen in small quarries from which road 

 metal is taken. Here the rock is found to be of reddish 

 brown to a purplish colour, and in sections on the shore 

 near Limerick Point it is of pale buff colour, with bands of 

 red jasper irregularly disposed through the joints. The rock 

 has a flne grained ground mass, containing minute felspar 

 crystals, but with abundant porphyritic crystals of orthoclase 

 and less frequent (juartz and brown mica. The large crystals 



