Frof. Dr. Ferdinand Roemer — A Visit to Ireland. 59 



Crinoidea. The beautiful cups of the Actinocrinus amphora and of 

 several species of the genera Platycrinus, Pentremites, etc., which 

 are scattered though many collections, derive their origin from this 

 place and neighbourhood. The quarries in the Carboniferous Lime- 

 stone, from which these fossils were formerly obtained, are not, 

 however, worked any longer at present, and the place is accordingly 

 closed up. With great difidculty only, could I obtain some small 

 examples of Pentremites Derbiensis, which appear on the weathered 

 surface of large blocks of limestone that are heaped up in wild con- 

 fusion under a steep limestone ridge. 



From Enniskillen we directed our way northwards in order to 

 view the remarkable and abrupt termination of the basaltic field of 

 Co. Antrim, where it reaches the sea. This basaltic plateau, which 

 spreads over more thau 800 square miles of the North of Ireland, 

 culminates in the Giant's Causeway, which, however, is not for the 

 geologist its most remarkable termination. The railway leading to 

 it runs through Londonderry, and then in a north-easterly direction 

 as far as Portrush, a small town best known as a watering place. 

 The Giant's Causeway is but a few miles distant from this. In the 

 immediate vicinity of Portrush several remarkable geological 

 phenomena are observable. A small rocky promontory is composed 

 of an igneous doleritic rock common in this district. At this 

 promonotory dai'k sedimeutaiy strata, slightly inclined, show them- 

 selves on the surface of the sea-shore, forming reefs extending 

 seawards. These are banks of dark grey rock composed of in- 

 durated clays, harder in some places than in others. It was with 

 astonishment that we perceived certain strata of this rock filled 

 with Ammonites and other characteristic fossils of the Lias ; for, from 

 the nature and position of the strata, one might have been inclined 

 to ascribe a far greater antiquity to them. The organic contents of 

 these strata indicate not only the presence of the Middle (?) and Lower 

 Lias, but layers of the Avicula contorta are visible, characterizing 

 the Ehsetic formation. This shell, first described and figured from 

 the North of Ireland by Portlock, has since been recognized as an 

 important characteristic fossil at many places in Central Europe. 



Eastwards from Portrush these Jurassic rocks disappear, and the 

 White Chalk, overflown by the basalt, makes its appearance, forming 

 grand scenery, which would not only rejoice the heart of the 

 geologist, but must also attract the admiration of the ordinary 

 spectator. Masses of snow-white chalk-rock a hundred feet high 

 face the sea in perpendicular precipices, crowned by the sharply 

 contrasted black basalt. Belemnitella mucronata and other dis- 

 tinguishing fossils make the geological position of the White Chalk 

 certain. The boundary between chalk and basalt does not by any 

 means run quite horizontal, but rises and falls in hills and hollows, 

 evidently because the surface of the chalk at the time of its being 

 overflowed by the basalt was very uneven. And so it becomes 

 clear how further eastwards towards the Giant's Causeway the chalk 

 disappears altogether, and the basalt descends to the level of the 

 sea. The Giant's Causeway is itself a small low promontory of 



