in the Basalt of Co. Antrim. - 343 



downwards from the surface of the flow. Every stage can be traced, 

 from tough dark ovoid masses to those that have left a crumbling 

 greenish residue, or have vanished altogether in a sort of sunset 

 glory of brilliant stripes and bars. If anyone, after a careful visit 

 to the Causeway area, remains unconvinced of this, an inspection of 

 the shore at Brown's Bay, Islandmagee, a locality probably well 

 known to Messrs. Tate and Holden, will assure him of the correctness 

 of the views of those authors, so far as the general origin of the red 

 zone is concerned. 



The whole matter of basaltic decomposition has, of course, received 

 new elucidation in the last few years from the studies on the 

 production of laterite in tropical climates, which have been published 

 in the Geological Magazine and elsewhere. Basalt, like almost any 

 rock containing salts of iron, will, under tropical conditions, rot 

 downwards from an ordinary terrestrial surface, giving rise to red 

 aluminous iron- ores. Seasonal rainfall doubtless helps this action ; 

 but it naturally goes on subaerially, and not, as Messrs. Tate 

 and Holden suggested, under cover of permeating waters. There is 

 now no difficulty in realising the formation in Eocene times of ten 

 or forty feet or more of red material, rich in iron and alumina and 

 relatively poor in silica, during the resting-stage in the volcanic 

 activity of our islands. The comparatively thin layers of pisolitic 

 iron-ore on the surface of the red zone may be conceived as formed 

 from time to time in pools that gathered during the rainy seasons. 

 The evidence for the existence of a warm climate in the Eocene 

 period over the area of the British Isles is considerably strengthened 

 by the presence of the red zone in J^orthern Ireland. 



In 1895 ^ I suggested that the pale bauxites of the county of 

 Antrim were derived from rhyolitic material. They appear typically 

 above the pisolitic iron-ore, thus effectually disposing of the idea 

 that the concretionary structure in the latter is due to metamorphism 

 by the Upper Basalt. John Kelly- acutely noted "clear quartz 

 crystals . . . with double pyramids complete" in the red zone at the 

 Bull's Eye Waterfall, some miles south of Glenarm. Mr. A. McHenry 

 has now (1908) observed these crystals and other quartz fragments, 

 which are clearly detrital, over a wide area between Glenarm and 

 Straid Hill ; they sometimes occur in a reddened bed, sometimes in 

 typical pale bauxite. The recent work of the Geological Survey tends 

 strongly to connect the pale bauxites with the decay of local rhyolite 

 of the Tardi'ee type ; and in many places we have to conceive the 

 formation of a sandy deposit, blown from crumbling rhyolitic surfaces, 

 and spread out as a comparatively^ thin layer over the lateritic Lower 

 Basalt. The parallel between this deposit and the sands accumulated 

 by wind on the surface of the basalts in the bush-land of the Central 

 Zambesi is one that appeals to the geologist, as affording a picture of 

 our own area in early Cainozoic times. 



The present paper, urging that the red zone was essentially formed 



' "The Ehyolites of the County of Antrim; with a note on Bauxite," Trans. 

 R. Dublin Soc, yoI. ti, p. 108. 



2 Op. cit., Proc. E. I. Acad., vol. x (1869), p. 303. 



