Notices of Memoirs — B. LI. Pmeger — Post-Glacial Deposits. 517 



The ground was first broken by rifts running from south-east to 

 north-west, and these were quickly filled by basic lavas. Flow 

 after flow emerged across the country, filling up the hollows carved 

 by denudation, and forming in time continuous plateaux. Although 

 a few explosive vents were established here and there, fluid basalt 

 was the great feature of these eruptions. A time of quiet followed, 

 when the lake-deposits and iron-ores of Glenarm, Ballypalady, etc., 

 were accumulated ; and sporadic outbreaks of rhyolite appeared, the 

 most prominent being that of Tardree Mountain. Then the basic 

 eruptions were renewed, and the columnar basalts of the Causeway 

 coast belong to this second epoch of activity. 



Mr. Starkie Gardner has referred these volcanic masses of 

 Northern Ireland to early Eocene times, from a study of the plant- 

 remains in the associated lake-deposits. Hence we find the marine 

 Cretaceous beds followed by a terrestrial and igneous Eocene ; and 

 possibly some of the latest vents were active in Oligocene times. 

 Thenceforward we know nothing of Irish geological history until the 

 Glacial Epoch, which has left such piles of Boulder-clay and gravel 

 across the country. The latest feature of interest is the blue marine 

 clay of Belfast and Magheramorne, full of exquisitely preserved 

 post-Pliocene fossils. This lies unconformably on the glacial drift, 

 and represents a comparatively recent submergence and re-elevation. 

 The raised beadh of Larne, with flint-chips in it prepared by man, 

 indicates the modern date of the movements of elevation. 



When we go south from the immediate neighbourhood of Belfast, 

 the Mourne Mountains rise conspicuously, their summits being far 

 more bold than those of the adjacent Caledonian granite ridge. 

 They are also formed of granite, which cuts across basic masses; 

 the latter are seen at Carlingford to be at any rate post-Carboniferous. 

 In turn, a few basic dykes of still later date traverse the granite. 

 By its relation to these two basaltic series, and its petrographic 

 identity with the Cainozoic granites of Mull and Skye, we need not 

 hesitate to regard the Mourne granite as of Eocene age. It forms, 

 then, as Mr. McHenry has pointed out, an interesting deep-seated 

 mass for comparison with the rhyolitic lavas of the inter-basaltic 

 epoch in county Antrim. 



From the above notes, which have no claim to originality, it will 

 perhaps be seen how attractive the Belfast area is to geologists, by 

 reason of its very contrast with the accepted types of Jurassic, 

 Cretaceous, and Cainozoic deposits, as known to us in the London 

 Basin. Those familiar, on the other hand, with the geology of the 

 Scottish Isles, will find many interesting points of similarity. 



IV. — The Post-Glacial Deposits of the Belfast District. 

 By R. Lloyd Praegee.^ 



THE silted-up head of Belfast Lough and other similar places in 

 the district display a remarkably fine series of deposits extending 

 from the close of the Glacial epoch to the present day, with a rich 



1 Abstract of a paper read before the British Association, Belfast, September, 1902, 

 in Section C (Geology). 



