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gore Head. Now, the red ochre beds at Bengore Head have many 

 hundred feet in thickness of various kinds of traps over them — amor- 

 phous, columnar, brecciated. The Sandy Brae porphyry has no rock 

 over it at all, nor does it appear that it was ever wholly covered over 

 with the trap of the country since its protrusion ; on the contrary, on 

 examining the country round its margin, it appears much more likely 

 that it was protruded immediately after the basalt, and is probably of 

 the same or the next age to Sleamish mountain, six miles northward 

 from it, which is newer than all the traps except the dykes. 



Making the Cushendall porphyry more recent than the tabular trap 

 seems erroneous, because the new red sandstone on the shore, at the 

 coast-guard station, at Ballisk, near Cushendall, contains in the con- 

 glomerate of its base abundance of pebbles and stones of the adjacent 

 Cushendall porphyry — a proof that the porphyry is older. As the new 

 red sandstone of Red Bay is older than the lias, the chalk, the tabular 

 trap and all, it follows that the Cushendall porphyry must be older than 

 the tabular trap, which is itself newer than the chalk, and rests on it. 



The sienite of Antrim appears to be put into too old a class in the 

 antiquity of the igneous rocks. Three veins of reddish-brown sienite 

 are seen in the Goodland cliff, near Murlogh Bay, and ascend to the top 

 of that rock, and penetrate the overlaying chalk at West Tor. This, I 

 consider the same rock, as the so-called granite. It is probably contem- 

 poraneous with all the dykes of sienite which penetrate the mica slate 

 along the shore from Cushendun to Murlogh Bay. There does not appear 

 to be any good reason for putting this sienite, which is newer than the 

 chalk, into an older class than the Cushendall porphyry, which was cer- 

 tainly anterior to it. 



This Antrim sienite appears to me to be in colour, grain, and com- 

 position, identical with numerous dykes of red felspar trap, which occur 

 in the country between Loch Kathrine and Loch Lomond, in Scot- 

 land. 



Whin Dykes. 



The subject of whin dykes demands a few observations. Lyell, in 

 his "Principles of Geology," vol. i., p. 364, describes a fissure on the 

 flank of Etna, between the plains of St. Leo and a mile from the summit, 

 at the commencement of the great eruption of 1 669. The cleft was twelve 

 miles long, and six feet broad, and was open to the surface. The fissure 

 gave out a vivid light, from which he, with great probability, concludes 

 that it was filled to a certain height with incandescent lava. After the 

 formation of this, five other fissures were produced, and emitted sounds 

 heard at a distance of forty miles. 



Our whin dykes appear to be generally like the fissures above de- 

 scribed — they are mostly vertical, but they are sometimes found sloping, 

 and sometimes horizontal — having been injected between the level beds 

 of sedimentary rocks. Instances of this kind occur at the Scrabo sand- 



K. I. A. PEOC. VOL. X. 2 TJ 



