316 



trap, and all, of about 800 feet, there being that difference of elevation 

 between the bed of chalk on the west brow of Knocklayd and at the 

 quarries at Ballycastle. Southwards from Cape Castle stream, this line 

 passes a little to the east of Armoy Church, and on towards Clogh mills. 

 The east side of the line of the valley seems here for some miles to indi- 

 cate its position, as chalk and trap occur on the west side at Balleny, 

 Limehill, Corkey, &c, &c. 



Of the Ages of Igneous Rocks. — Sir Eichard Griffith says in the 

 " Dublin Geological Journal," vol. i, p. 155 : " It has been long known 

 that granite, sienite, and traps are of different ages." On close exa- 

 mination of the great trap district of Antrim, he thinks that that district 

 has been the theatre of eight distinct epochs, and he gives the result of 

 his observations in an ascending order, as follows : — 



1. Granite. i 6. Cushendall porphyry, 



2. Sienite. 



3. Lower tabular trap. 



4. Sandy Brae porphyry. 



5. Upper tabular trap. 



7. Intruded mountain masses 

 of trap. 

 Trap dykes. 



The succession of some of these is very clear, and cannot be mistaken. 

 On such of them as are obscure he appears to me to have come in some 

 cases to very doubtful conclusions, and in some to positively erroneous 

 ones. 



To begin with the granite, the rock which Sir Eichard calls by that 

 name, occurs on the shore at Castlepark, half a mile north-east of 

 Cushendun. He says,* u It is of a brownish red colour, containing 

 large crystals of glassy felspar." Again, " Its general structure is por- 

 phyritic, and occasionally the crystals of brownish red felspar are large 

 and beautiful. At Ardsillach, a mile nortb-west of the same place, there 

 is a mass of it about 50 feet thick, intruded between, and parallel with, 

 the beds of mica slate, as a subordinate rock. If this reddish rock oc- 

 casionally assumes the character of a porphyry, it cannot be called a true 

 granite. In fact it very closely resembles the felspar trap of the veins on 

 the coast between Cushendun and Murlogh Bay, in colour, and every- 

 thing except the mica. I believe them to be all the same rock which has 

 been protruded through the mica slate on this coast, and which, when it 

 occurs in larger masses than usual, has mica developed as well as large 

 crystals of glassy felspar. If these views be correct, it is newer than 

 the chalk, for the red felspar trap veins penetrate that rock at Tor 

 Escort, near Murlogh Bay. The pebbles of red granite got in the new 

 red sandstone conglomerate at Eed Bay, and brought forward as proof 

 of its age, may have had another source. True granite of a very red 

 colour occurs for several square miles about Eathfriland, in the county 

 of Down. 



He places the Sandy Brae porphyry between the lower and upper 

 tabular traps, and the equivalent of the red ochre, on the coast at Ben- 



* "Dublin Geological Journal," vol. i., p. 156. 



