^54 



SCIEXCE-GOSSIP. 



we proceed westwards, until at Kenbane Head it 

 has an altitude of only 400 feet. This promontory 

 contains some very fine caves excavated in the 

 chalk, and these are occasionally accessible in good 

 weather. The Isle of Rathlin, five and a half miles 

 from the shore, affords us an illustration of columnar 

 structure, while the islet of Carrig-a-Rede, separated 

 from the mainland by a fissure eighty-five feet 

 deep and sixty feet wide, presents an equally 

 good example of the amorphous type. From Carrig, 

 the whole of the shore line from Fair Head to the 

 Causeway is visible. Plaiskin Head, the highest 

 portion of which 

 is " Hamilton's 

 Seat" (366 feet), 

 is a little to the 

 west, and this 

 promontory 

 gives us the best 

 opportunity for 

 studying the 

 various sheets of 

 igneous rocks 

 which have been 

 spread in suc- 

 cession upon the 

 underlying 

 chalk beds. No- 

 thing is visible 

 in the cliff but 

 what is of igne- 

 ous origin, and 

 the varieties and 

 thickness are as 

 under : 



Photo 6vl 



Tilt Lady s Fan. 



Amorphous Basalt and Ochre Beds 

 Columnar 



Amorphous ,, second series 

 Columnar ,, ,, ,, 



Ochre and Laterite 

 Greenstone (also igneous), of varied 

 structure 



Total 



Feet 



60 

 60 



36; 



The appearance of the various beds with their 

 galleries and columns reminds one of some over- 

 whelmed and disinterred city of the East. 



It is advisable to proceed from Plaiskin to the 

 Causeway by road, as the cliffs gradually lose their 

 imposing appearance and give place to a com- 

 paratively low shore. An easy walk soon enables 

 us to view the ground on which so many specula- 

 tions and traditions have been reared. There are 

 "The Chimney Tops," detached " stacks " rising 

 forty feet above the neighbouring pillars. Another 

 series rising from a common ledge to a height of 

 120 feet, bears the name of " The Organ," while 

 on the Causewav itself we have the Giant's 



"Chair," "Well," "Pulpit," "Skittle-alley," and 

 so on ad infinitum. We pass through the Giant's 

 ' ' Gateway ' ' and immediately find ourselves upon 

 the Causeway. This is divided into three portions, 

 denominated Grand, Middle, and Little Causeways. 

 A superficial view of the more limited area is apt to 

 disappoint ordinary visitors who find it to possess 

 a less imposing appearance than their fancy had 

 pictured, but this disappointment cannot be 

 shared by any who look at it in the light of 

 geological knowledge. In all it is about 400 yards 

 long and at its highest point is forty feet above 



sea level, gradu- 

 ally sloping to- 

 wards the water. 

 It has been esti- 

 mated that the 

 exposed pillars 

 number over 

 40,000, and the 

 majority of 

 these are practi- 

 cally perfect in 

 shape. They 

 vary in form, 

 but most of 

 them have six 

 sides, many have 

 seven and eight, 

 three have nine, 

 while only one 

 has been found 

 with three sides. 

 They are all 

 quite closely 

 packed together, the space between them being 

 usually so small as not even to admit of the 

 insertion of a knife's blade. The average diameter 

 is about eleven inches, but the thickness of the suc- 

 cessive slabs forming the columns varies con- 

 siderably. 



The Causeway is simply a continuation of the 

 first series of pillars mentioned as occurring at 

 Plaiskin Head, the upper extremities having 

 become exposed by the removal — by water action 

 — of the top sheet of amorphous basalt and the ochre 

 beds. The rock is practically homogeneous and 

 consists of a fine mixture of augite, labradorite, 

 and a small percentage of magnetite. Zeolites are 

 fairly numerous in the larger cavities as are 

 varieties of chalcedony in the smaller bubble 

 holes and veins. 



The sheets were evidently poured out upon dry- 

 land, but the volcanic centre has not yet been 

 identified. There is every reason to believe that it 

 occupied a position now covered by the sea north- 

 west of Antrim. From a careful comparison of 

 the "leaf beds" enclosed between the successive 

 sheets, geologists conclude that the igneous rocks 



IR. Welch, Belfast. 

 Giant's Causeway. 



