60 A DESCRIPTION OF THE [Ch. V. 



grey colour, and interlaced fibrous texture, yet disposed in 

 laminae, forming a slate. It is soft, yet tenacious, works 

 easily under the chisel, and hardens in the fire : it is quarried 

 and wrought for various economical purposes." * 



" Hornblende, in crystals disseminated through this mica- 

 slate, is by no means uncommon ; and sometimes this mineral 

 becomes so intimately mixed with the slate as to constitute a 

 compact tenacious compound; as, for example, in Aghole 

 mountain. Beds of common hornblende probably occur also 

 occasionally in the mica-slate, as detached blocks of that rock 

 are sometimes to be seen ; for instance, in the northern part of 

 Carrigacrow, and in the lower part of Balreagh glen, towards 

 Glencree river ."f " Brisselstown Hill consists of mica-slate, 

 fine granular greenstone, greenstone-slate, and greenstone 

 porphyry. Mica-slate appears on the eastern side of Brissels- 

 town, beneath which is seen the granite base; but the southern 

 side and summit are composed of the trap rocks just men- 

 tioned, principally the two first, which form a great bed in 

 the mica-slate. This slate in the western part is porphyritic, 

 containing numerous crystals of felspar, and it passes into 

 greenstone porphyry by an intimate mixture of hornblende. 

 This gradation from mica to hornblende is frequently observ- 

 able in these rocks." J " On the southern side of Comaderry 

 mountain are masses of trap rock : the higher part consists 

 mostly of common hornblende rock, which varies in colour 

 from green to black, and approaches even to the nature of 

 massive mica. About the middle of the declivity, it is inter- 

 mixed with felspar, mostly compact, and greyish white, the 

 two substances constituting a coarse-grained rock ; at times 

 the felspar greatly predominates, containing hornblende and 

 mica disseminated in its substance. Lower down the hill, the 

 rock consists of a compact felspar base, with prismatic crystals 

 of hornblende interlaced, and shooting through the felspar 

 in every direction." 



* Geol. Trans., vol. v, p. 146. f Idem, p. 154. J Idem, p. 161. 



Idem, p. 147, 



