pullished respecting Antrim, Derry, ^c. 279 



in the bed of Glenarm River, mentioned by Dr. D. 

 preF. xii. 



Dr. W. H. Drummond's description of these strata and 

 their imbedded contents, pref. p. x. is as follows : " Over- 

 topping all (the Limestone strata) is the (jreat stratification 

 of Trap, with its subordinate divisions of Greenstone, Por- 

 phry-\late, Trap-Tvffa, and Amygdaloid. The solid Trap 

 and the Amygdaloid alternate, as may be distinctly seen at 

 the Knockaoh, the former showine; traces of incipient co- 

 lunmariiv, the latter less rent into (bv) fissures, often very 

 friable, and indented at its junction with the Trap; thickly 

 studded with Zeolite, and of a dark gray, brown, or reddish 

 colour. It would require fn-quent nnnute examinations to 

 ascertain the order in which the different numerous strata 

 of tiiis formation succeed each other. There is also a 

 stratum of an ochreous vcrniillion led sxihsiance which may 

 be ^een at the base of t!ie precipice of the Cave Hill, but 

 in much greater beautv and extent at Murlogh and the 

 Giant's Causeway. The Porphry- slate, which may be 

 easily distinguished by its slaty Iraclure, is ornamented with 

 small topaz-coloured crystals of C/»'?/jo//7e or Olivin. Small 

 brilliant crystals like Sapphires, and opake crystals oi' Skorl, 

 are found in some varieties of the IVap ; that of F'air-head, 

 which !S so coarse as to resemble Granite, contains Augite. 

 The vesicles of the amygdaloid are almond-shaped, tubu- 

 lar, quadrantriilar, and a series of them is often connected 

 together. Thcv are supposed to have been formed by air- 

 bubbles during the deposition of the strata, and to have 

 been afterwards filled or lined by percolation with the 

 matter by which they are now occupied. This is, Steatites, 

 calcareous Spar, Calcedony, Opal or Zeolite : the last is very 

 prevalent: it is sometinies cubical, often stelliform, and 

 in the beauty, delicacy, and the arrangement of its crystals, 

 vies with the Thistles' do>vn. As the character of Basaltic 

 or Whinstone Mountains, the flatz-trap formation of Wer- 

 ner, are too obvious to be mistaken, the description of one 

 may serve for the whole. On one side they generally pre- 

 sent a steej) precipice, and on the other fall aw^y with a 

 gradual slope*. They are flat at the summit, whence they 

 are denominated Tabular." 



A bed of prismatic Basalt at Portrush and the Skerrie 

 Islands, is full of Belemnites and of Pectenites, and above 

 z\\,oi Cormia Ammoniiy dispersed through the whole mass, 



* What stratififd Mountains, in denudated districts in particular, do not 

 present tlieic C)iaracter»? more or les» perfectly, as their upper stratum is 

 utrm.inenl or otherwise ? that i*', will cr will not erdure the weallier. 



vol. 



