98 Guide to Belfast. 



The district generally is covered with drift and bog, so 

 that the relations of this rock to the basalts, or the exact 

 extent of it, are somewhat undetermined from direct field 

 observations. The main exposure of the rock is to be found 

 in the quarry on the south side of Tardree Mountain ; here 

 the rock shows a well-marked columnar structure, which 

 readily allows of quarrying operations. It is used locally 

 for building purposes, the smaller blocks being for paving. 

 The rock is here of greyish colour, is compact in character, 

 free from fluidal or banded structure, but contains many 

 porphyritic crystals of glassy sanidine, plagioclase, quartz, 

 occasional mica, and much trydimite. The quarry to the 

 north-east of Tardree Mountain is less compact in the char- 

 acter of the rock; bands of brown and green traverse the 

 rock sometimes along evident cracks parallel to the banding. 



The rocks exposed on the hillsides to the south-west 

 at Carnearny are fluidal rhyolite and spherulitic obsidian 

 traversed by perlitic cracks. 



Sandy Braes is not located on the smaller scale maps, but 

 may be easily found by leaving the main road from Doagh 

 to Kells.just opposite the Tardree inn, and taking a by-road 

 to the east. Close to this is a large surface excavation in 

 pink and bluish rhyolite, well banded and with well-marked 

 planes of flow. The rock breaks up readily, and decom- 

 poses along the numerous small and irregular joints, so that 

 the quarry is used for the supply of gravel. Going further 

 east the roadside heaps yield many weathered specimens of 

 fluidal obsidians, weathering to a dull grey colour. Surface 

 excavations through the fields and along the drainage lines 

 will give the only opportunity of seeing the rock in situ. 

 Near the top surface the obsidian weathers to a fine gravel, 

 but further down many large blocks of brilliant and compact 

 obsidian are readily found. The openings are too small 

 and sporadic to be located for permanent reference, but 

 from their abundance many different varieties of acidic 

 material may be collected. 



Other exposures of rhyolite occur at Eslertown, Kirkin- 

 riola, Cloughwater, to the north-west of Tardree, while to the 

 south-east there was a fine section visible in a quarry at 

 Templepatrick. Of their composition Professor Cole says : 



