12 



THE GEOLOGIST. 



first, aB the result of vertical pressure applied to the columns after 

 their perfect formation, and before the mass had quite lost its 

 plasticity from heat; secondly, the effect of a re-heating and 

 compression on the columns by an incandescent mass of trap being 

 poured out on them, thus rendering them plastic to a certain depth 

 only, an idea not improbable when it is recollected that basalt fuses 

 at a less heat than that required to melt pig-iron. Near Portrush, on 

 the Coleraine road, an excavation into a low knoll of amorphous trap, 

 the base of which is formed of a thick bed of columnar basalt, affords 

 a striking example of perfectly formed vertical columns being bent 

 over at the top to the depth of a few feet, most likely the re- 

 sult of their having been re-heated and compressed by the super- 

 imposed amorphous trap. The foregoing remarks have of course no 

 reference to columnar masses which exhibit a radiating structure, as 

 this may be merely a rude zeohtic form of columnar arrangement, or 

 crystallization in the basalt. 



Leaving the Causeway, and proceeding along the base of the cliffs 

 south west towards the headland called " Weirs snoot," (two hundred 

 and eighty-five feet in elevation), we soon pass off the Causeway-bed, 

 as it rises to that direction, or, in other words, slopes to the east- 

 ward ; and, as we get near the Hotel, the pathway under the cliffs ex- 

 poses the lost ochre bed of the Chimney-headland ; it is here, 

 however, very thin, and is overlaid by the western extension of the 

 amorphous trap which was described as resting on the '* Organ"-bed, 

 or that which forms the Giant's Causeway. The base of this amor- 

 phous trap is rudely columnar to the height of from eight to ten feet 

 from the ochre-bed, the sides of the imperfectly formed pillars being 

 deeply waved or curved, giving them a pinched look. Many of these 

 columns if detached would resemble a long irregularly shaped wedge 

 or pyramid, the base or apex being up or do^vn as chance would 

 have it. 



The exceedingly close resemblance of tliis rudely columnar mass 

 to that of the Rowley Hill, near Dudley, in Staffordshii^e, is very 

 striking, though they are of different geological age. 



The rugged headland to the north of the Causeway Hotel, called 

 " the Great Stcucan," and the chff' called " Weirs snoot," are formed 

 of the amorphous basalts which undei'Ke the oclu-e-bed, and eon- 



