E. T. Hardman — Fossiliferous Beds of Lough Neagh. 215 



Although drift deposits are well exposed in the vicinity and along 

 the shores of the lake, no similar clays are to be seen amongst them. 

 And on the whole, without further investigation and more con- 

 vincing proofs, I am unwilling to admit that the deposit I described 

 can belong to the Glacial period, seeing that it resembles in every 

 respect the lacustrine clays, while totally differing from the drift 

 beds. 



5. Age and Mode of Formation of Lough Neagh. — Even if we 

 should be obliged to reject the lacustrine origin of the Crumlin 

 deposit, I confess I cannot follow the argument by which as a 

 sequitur Mr. Swanston endeavours to quash the theory formerly 

 proposed by me with respect to the age of the lake. This particular 

 deposit cannot affect that theory one way or the other. If there is 

 anything geologically certain, it is that Lough Neagh occupies a 

 depression primarily caused by large faults which occurred after 

 the latest sheets of basalt we are acquainted with had been poured 

 forth. 1 This is sufficiently clear from the fact that the upper 

 basalt is brought down against the lower, as at Templepatrick and 

 Shane's Hill. It is also capable of proof that the Lough Neagh clays 

 (the lacustrine origin of which has never been doubted) are later 

 than the basalt, and older than the drift, which covers them in 

 many places. Also that they are the delta of one or more rivers 

 flowing from the southwards after a considerable area of country 

 had been denuded of the basalt which formerly extended at least as 

 far as Slieve Croob and the Mourne Mountains. Mr. Swanston, 

 however, prefers to consider the lake as of intra-Miocene age ; and 

 as a consequence of the supposed Glacial age of the Crumlin deposit 

 — but why, I am unable to conjecture — places the Lough Neagh 

 pottery clays as contemporaneous with the lacustrine iron-ore 

 deposits of Antrim, etc. He forgets that first the Lough Neagh 

 deposits are proved to be 300 feet thick. 2nd. That the depression 

 of Lough Neagh is more than 1,700 feet, and that it would certainly 

 have been filled up by the next flow of basalt. 3rd. That the 

 faults around it, some of 500 feet, which must have altered the face 

 of the country considerably, are post-basaltic. And last, but not 

 least, that the Lough Neagh deposits are totally different in every 

 respect from the ferruginous deposits of Antrim. 



The iron-ore beds of Antrim were formed in a series of shallow 

 depressions by the denudation of the basalt itself. By a well-known 

 series of chemical changes the basalt yielded soluble carbonate of 

 iron, which, being carried into these shallow " broads," was oxidised 

 and deposited as hydrated oxide of iron, subsequently dehydrated. 

 According to the freedom or otherwise of the lake from silt or mud, 

 rich iron-ore, lithomarge or aluminous ore was produced. All these 

 deposits are rich in iron, and are not of great thickness. 



With these the Lough Neagh clays have nothing in common. 

 They consist simply of clay, more or less sandy, usually very light 



1 For full details on this and the following statements see " On the Age and Mode 

 of Formation of Lough Neagh," Brit. Assoc. Kep. 1874, and Journ. Eoy. Geol. 

 Soc. of Ireland, vol. iv. pt. iii. new series. 



