Department of Agriculture and Technical Instruction for Ireland. MEMOIRS OF THE GEOLOGICAL SURVEY OF IRELAND. THE INTERBASALTI C ROCKS (IRON ORES AND BAUXITES) OF NORTH-EAST :DNALER-I ’ BY G. .A Jc. ,ELOC F.G.S. ; .S B. NOSNIKLIW ; ALEXR. M‘HENRY, M.R.I.A.; J. R. ,EORLIK ;.1.cS.C.R.A .H J. SEYMOUR, B.A., F.G.S.; C. .E MOSS, D.Sc.; .W D. ,HGIAH .1.cS.ChI.A AND NILBUD : PRINTED FOR SIH S’YTSEJAM YRENOITATS ,EOIFFO BY BROWNE & NOLAN, LTD., UASSAN STREET. And to be purchased from ; E. STANFORD, 12,13 and 14L ONG ACRE, LONDON : W. 8t A. K. JObNSTON, LTD. , 2 ST. ANDREW SQU~\RE,E DINBURGH HODGES, FIGGIS & CO., LTD., GRAPTON ST., DUBLIN. From any Agent for the sale of Ordnance Survey Maps, or through any Bookseller from T. FISHER UN WIN, 1 ADKLPM TERRACE, LONDON, W.C., who is the sole tiholesale Agent to the Trade outside the County of London. __ PREFACE. NUMEROUS references to the interbasaltic beds of northern Ireland occur in the previously published Memoirs of the Geological Survey. At the time, however, that these were written, the aluminium in- dustry had not developed, and the analogy between many red , laterites and the material known as bauxite had not been generally realised. The growing demand for iron ores has also made it desirable to reconsider those of northern Ireland, and the Geologists of the Survey, in 1907 and 1908, examined in detail the horizon where such ores are already worked, or where they may be expected to ,occur. The results are represented on the maps accompanying the present Memoir, which may be taken as replacing the hand-coloured geological maps of the same areas, so far as the interbasaltic beds are concerned. The principles on which the revision of the interbasaltic series was undertaken will be best explained by the following extracts from a circular letter issued to the Geologists on 1st June, 1907 :- “ (i) The interbasaltic beds occur at various horizons, but mainly in a zone representing a presumably prolonged epoch of repose between two epochs of considerable volcanic activity. (ii) The attention of the Geologists will mainly be given to this . zone, marked by beds of-iron ore, bauxite, and deep de- composition of the underlying basalt. (iii) The recent and numerous observations on laterite in various countries show that many of the red beds hitherto classed as iron ores contain sufficient aluminium hydrate to render them, now or at some future date, of value as ores of aluminium. (iv) The source of these beds may in some cases be found in the underlying basalts, in other cases in material brought from some distance and accumulated in lakes. The formation of laterite in tropical climates as a surface-crust, and possibly in connexion with alternating dry and rainy seasons, should not be lost sight of, even in cases where the lacustrine view has been put forward. J(v) In Co. Antrim local eruptions of rhyolite occurred in the comparatively quiet interval. Pebbles from these centres of activity may be found in interbasaltic beds, and are already known from the Glenarm area. >iV The mode of decomposition of these rhyolites makes it probable that the light-coloured bauxites were derived from similar lavas poor in iron. (vii) Plant-beds are well-known in certain places. Remains, of land-molluscs or other animals would be of great assistance, if discoverable. The interbasaltic beds are the only guides we uossess in determining the geological age and duration of the eruptive period. (viii) Local records of rumours of “ coal ” having been raised in this or that spot are common in the north of Ireland. . . . . 111 These should beiinvestigated, as they may lead to the discovery of new beds of lignite ; hence also of new laterite or bauxite layers. ..I (ix) I The amount of exploration among the iron-ores and bauxites since the original geological maps and memoirs were prepared is already known to have thrown new light on the area occupied by these deposits ; hence a revision of boundaries and the tracing of new ones may be necessary. (4 But, on the whole, the present examination will be mainly concerned with the vertical series of deposits present at any point. The history and succession of the beds in the locality may then be traceable, as well as their horizon in the great basaltic series.” While no general revision of the volcanic region seemed necessary, the relations of the Upper to the Lower Basaltic Series naturally affect the question as to where the iron ore zone is likely to occur. Mr. J. R. Kilroe believes that the Upper Basalt may have a westerly extension, as was also suggested by Mr. Egan for the district of Benevenagh. Mr. Kilroe’s views on this matter are stated in an appendix. From the point of view of the geological history of Ireland, the main interbasaltic zone, with its plant-beds and contemporaneous eruptions of rhyolitc, offers features of peculiar interest. The Survey has obtained from Dr. C. E. Moss, of the University of Cambridge, a review of the evidence afforded by the flora, so far as known. The cautious attitude adopted in this chapter will be appreciated even by those who are more hopeful than Dr. Moss of the results of studies among Cainozoic plant-remains. Thanks are due to the Council of the Belfast Natural History and Philo- sophical Society, and to Mr. William Swanston, F.G.S., for the loan of valuable specimens. In Chapter VII, sixty-four analyses of materials from the inter- basaltic zone have been brought together from widely-scattered sources. Other analyses probably exist, as is shown by the publica- tion of some of these in the first instance in France and Germany. These analyses, though they vary in importance, will serve for comparison with those of similar materials worked in Europe, Asia, and America. This comparison has been facilitated by information as to the Indian ores, kindly given by Sir T. H. Holland, F.R.S., late Director of the Geological Survey of India, when on a visit to Ireland in 1.906. Mr. James Strachan, of Ballyclare, Analyst and Microscopist to the North of Ireland Paper Mill Company, has made detailed studies of the Antrim volcanic series, and has been so good as to furnish many useful suggestions, especially as to the part played by bacteria in the precipitation of iron ores from solution in natural waters. Plates IL-VI. are from photographs by Prof. H. J. Seymour. GRENVILLE A. J. COLE, Director. DUBLIY, February, 1912. V TABLE OF CONTENTS. -- tEGAP PREFACE . . . . . . . . . . ii CHAPTER I. THE NATURE DNA SNIGIRO FO EHT -RETNI CITLASAB BEDS OF NORTHERN IRELAND I Progress of Observation on the Interbasaltic Zone 1-14 General Conch&ions’ inIr&ard t’o the-Inter: basaltic Zone . . . . . 14.-15 CHAPTER II, TRE NORTHERN DISTRICT. INTRODUCTION 16 The Giant’s Causeway and Bengore Head 17-19 Outcrop inland between Cloyfin and Bally- castle, including Ballintoy . . 19-24 . - . . . . . Knocklayd 24 . . . . . Killagan Bridge 24 Occurrence of Bole at various Horizons in the Basalt of the Northern District 25 Adit at the Junction of the Chalk and overlying Basalt at Downhill, Co. . Londonderry 26 Note on the Occurrences of &on bre ai . Keady Mountain and Bohilbreaga 26 CHAPTER III, THE EAST ANTRIM DISTRICT. INTRODUCTION 28 . . G lenarm Area 28-32 1 : : . . Shanes Hill Area 33 . . . . . . Scawt Hill 34 . . Larne and Island Magee 34-36 . Ballynure and Straid (Irish Hill) Area 36-38 The Iron Ore Zone near Lough Mourne, . . . north of Carrickfergus 39 Pisolitic Iron Ore below-the Lower Basalt 39 Changes in Geological Boundaries necessi- . . . tated by the revision 40 CHAPTER IV. THE MID -ANTRIM DISTRICT. GENERAL . . . . . DESCRIPTION 41 . . . . . Mining Areas 42 . . . . . Glenravel Mines 43-46 Crommelin Mines, including Tuftarney Hill . . . . . . 46-52 . . . , Evishacrow Mines 52 . . . . . Parkmore Mines 53-55 . . Carncormack and Slievebane Area 55 . . . . . Ardclinis Mines 56 . . . o . . Bay Mines 57-59 . o D . . Gienariff Mines 59 . . . . . Cargan Mines 60 . . . . Dungonnell Mines 61 . . . . Mountcashel Mines 64 Rathkenny Mines . . . . . 66-69 < . . . . . Correen Mines 69-7 1 v CHAPTER IV.-con. Clonetrace Mines . . . . . 7 l-74 Cleggan Tract . . . . . 74 Cullinane Mine . . . . . 76~78 Carnlough Mines . . . . . 78-80 Evidence of Fossil Vegetation in the Mining Areas . . . . . 80 Outlying Tracts . . . . . 80 Berk Hill Outlier . . . . 80 Black Hill Outlier . . . . 82 Cullaleen Hill . . . . . 84 Tully Hill Outlier . . . . . 85 Carmagrim Out,lier 86-88 Original Surface of Lowkr Bakalt ii Mid: Antrim . . . , . 88 CHAPTER V. THE SOUTHERN DISTRICT . . . 89 Lyles Hill . . . . . . 89 Knowehead . . . . . 91 Ballypalady (Ballymartin) . . 91 Tardree Area . . . . . 93-98 Eslerstown . . _ . . . . 98 Ballycloughan, Kirkinriola, and Clough- water . . . . 99 The Lough keagh' Clays and Associated Lignites . . . . . 99-101 The C&gh Conglomerate . . . 101-103 CHAPTER VI. THE PLANT-REMAINS OF THE INTERBASALTIU ROCKS OF Co. ANTRIM . . . 103-111 CHAPTER VII. ANALYSES OF MATERIALS FROM THY INTER- BASALTIC BEDS OF IRELAND . . 112 APPENDIX I. ON THE QUESTION OF THE WESTERLY EXTENSION OF THE: UPPER BASALTS IN IRELAND . . . . . 120 APPENDIX II. NOTE ON THE PROBLEM OF THE Louc~ NEAGH CLAYS . . . . 121 INDloX . . . . . . . . . 127 vi LIST OF ILLUSTRATIONS. PLATE fibI.-Cliff east of the Giant’s Causeway. l+ontispiece #, II.-Spheroidal Basalt decomposing into Bole and Lithomarge. Pathway to the Giant’s Cause- way from Bushrnills . . . . . p. 18 ,, III.-Lithomarge of the Interbasaltic Zone at the Giant’s Causeway, showing residual Cores of Basalt, and concentric banding, with fluidal structure marked by amygdaloidal layers, in the lower part . . . . . . . p’ 19 ,# IV.-Spheroidal Basalt, decomposing into Lithomarge, Brown’s Bay, Island Magee . . . . p. 34 I# V.-Details of Spheroidal Basalt, decomposing into Lithomarge. Brown’s Bay, ‘Island Magee . p. 35 ., VI.-The Ore Zone (just above the mineral railway), Parkmore . . . . . . . p. 53 --- FIGURES IN TEXT. Fig. I.-Index Map of Area described . . . . p. 16 ,, 2.-Section at Libbert Bauxite Mine in 1879 . . p. 31 ,, 3.-Diagrammatic Section across the faults south-cast of Scawt Hill . . . . . . . p. 34 99 4.-Section from Larne Lough to Brown’s Bay, gniwohs the position of the Iron Ore . . . . p. 35 ,, &-Sections at Irish Hill . . . . . . p. 37 99 6.-Section through Irish Hill,’ Straid . . . . p. 38 ,, ‘I.-Section west of the Office, Glenravel Mines . . p. 45 ,, S.-Section in Stream above Newtown Crommelin . . p. 47 ,, 9.-Section in Solomon’s Drift Mine . . . . p. 48 ,!, lO.-Section in six-feet le-~~1,S olomon’s Drift Mine . . p.- 49 ,, 11.-Section in Solomon’s Drift Mine . . . . P. 50 ,, 12.-Segregation of White Material in Bauxitic Clay . . p. 51 ,, 13.-Diagram of the Dungonnell Mining District . . p. 63 Y, 14,--Section at Evishnablay Mine, in 1886 . . . p. 64 ,, l&-Section at the Buck Burn . . . . . p. 65 t, 16.-Section in Rathkenny No. 1 Adit . . . . p. 67 *, 17.-Geological Map of the Cullinane RIining Area . . p. 77 71 I&-Geological Map of the Berk Hill Outlier . . . p. 81 9, 19.-Geological Map of the Black Hill and Cull&en Area p. 84 ,, 20.-Geological Map of the Tully Hill and Carmagrim Outliers p. 87 ,, 21.-Section at Lyles Hill, near Templepatrick . . p. 90 9, 22.-Section in Railway, Ballypalady . . . . p. ‘92 ,, 23.-Ideal Sections in the Tardree Area . . , . p. 97 EHT INTERBASALTIC ROCKS (IRON ORES AND BAUXITES) OF NORTH-EAST IRELAND. CHAPTER I. THE NATURE AND ORIGINS OF THE INTERBASALTIC BEDS OF NORTHERN IRELAND. . BY GRENVILLE -4. J. COLE. PROGRESS OF OBSERVATION ON THE INTERBASALTIC ZONE. The occurrence of a zone of apparently stratified rock in the midst of the basaltic series of northern Ireland was fully apparent to the early visitors to the Giant’s Causeway. The bright red colouring of the band half-way up the cliffs, in contrast with the brown and black joint-faces of the basaltic lavas, at once attracts interest and attention. In recent years the excavation of a path along the red zone has made it more accessible, and the separation of the basalts into an upper series of massive columnar lavas and a lower series of thinner flows is impressed upon everyone who walks eastward from the Causeway. Though seams of red or ochreous clay occur at various levels in the Lower Basaltic series, it became gradually realised that these materials were mainly developed during a particular epoch, when the volcanic activity that gave rise to the basalts of northern Ireland died down for a time, and a broad surface of lavas became exposed to weathering. The beds of. the red zone were known at an early date to include the argillaceous rock called “ lithomarga “* or lithomarge, and the zone itself was traced over a wide area, from west of the Giant’s Causeway to Glenarm and Island Magee. f In 1843, attention was called by Mr. Crommelin, of Newtown Crommelin, to the iron ore of his district, and in 1861 Dr. Ritchie mined as an aluminous flux the fragmental iron ore of Ballypalady . In 1873 or 1874, through Mr. Walter Jameson,: * G. V. Sampson, “Memoir of the Chart and Survey of Londonderry ” (1814), p. 103. t An interesting account of the deveIopment of the iron-mining industry in Antrim is given by J. F. Hodges, Proc. Belfast Nat. Hist. and Phil. Sot., 1876, pp. 1-8, and Appendix to Geol. Surv. Mem. to sheets 21, 28, and 29, p. 47. $ See G. H. Kinahan, “ Iron Ore Measures of Co. Antrim,” Trans. Manch. ; Geol. Sot., vol. xxii. (1893), p. 458 and “ Antrim Alumyte,” ibid., vol. xxiii. (1895), p. 165. See also Kinahan, “Additional Notes on AIuminium and its .p Ores,” ibid., 172. 2 certain pale grey or greyish brown deposits, found here and there above the iron ore, came into notice, as containing far more alumina and less silica than ordinary clays. These were compared aptly with the bauxites of Les Baux and other localities in the south of France, and were used, under the name of “ alum- clay ” or “ alumite,” for the production of alum. Still later, the development of the aluminium industry led to the use of some of these materials as aluminium, ores ; but so far it seems to be found more economical to prepare alumina from French bauxite in the works that were established at Larne for the exploitation of the Irish rock. Lignites and plant-beds were observed on the same horizon as these interesting deposits, and have given rise to many stories of the discovery of coal in northern Ireland. A succession of observations has shown, moreover, that eruptions of rhyolite, long ago described by Richardson, J. F. Berger and others,* occurred during the epoch of comparative rest. The horizon of these rhyolites was correctly recognised by Sir R. Griffith t so far back as 1836, when he stated that the porphyry of Sandy Braes was formed “ in the series of epochs between t,he lo.wer and upper tabular traps.” It would accord with views prevalent among petrologists if it could be urged that the basalts and rhyolites of northern Ireland, and hence also the gabbro of Carlingford and the granite of the Mournes, originated by differentiation in a common cauldron. We must, however, be content to state, as Whitman Cross $ has done for a similar seouence in Hawaii, that there is as yet no evidence in favour oi such a supposition. The mode of origin of the interbasaltic beds of northern Ireland has been a matter of much discussion and it has become necessary to revert in recent years to opinions held by observers at the opening of the nineteenth century. Faujas de Saint-Fond 6 was one of the first to note how basalt may pass by decomposition into red bole or grey clay. He found a clay, with all the structure of basalt, on “ .Mezinc ” (M6zenc) Mountain, south of Fay-le- froid in the Cevennes ; this clay adhered’to the’ tongue and was easily sectile. Saint-Fond thus enables us to trace the con- nexion between lithomarge and basalt, the passage taking place in situ on the surface of the flow. He also refers to an _ observation by Sir William Hamilton in lW1 11 a's to the produc- tion of a white earth from basalt, through the influence of the * W. Richardson, “ On the Alterations . . . in the Structure of Rocks,” ; etc. Phil. Trans., 1808, p. 211 Berger and Conybeare, “ Geological Features of N.E. Counties of Ireland.” Trans. Geol. Sot. Lond., vol. iii. (1816), p. 109. t Address, Journ. Geol. Sot. Dublin, vol. i., p. 158. $ Journ. of Geol., vol. xii. (1904), p. 520. 3: “ Recherches sur les volcans eteints du Vivarais et du Velay ” (1778), pp. 196-7. 11P hil. Trans., 1771, 5th May. solfatara of Pozzuoli. The Rev. William Hamilton,* who courage- ously; supported Desmarest’s view of the volcanic origin-of the Antrim basalts, wrote that “ an extensive tribe of clays ” arise from their decomposition ; but he was attracted to”the idea that the ochre beds had resulted from the igneous alteration of a ferruginous earth. His opponent, the Rev. W. Richardson, claimed to be not a Neptunian nor a Vulcanist nor a Plutonist ; t but his views on basalt decidedly helped the Neptunian cause. He maintained, however, justly that the red strata had “ been once pure basalt,” stating- this in an unpublished memoir read before the Royal Society oft Edinburgh, and again in 1803.$ Richardson became much interested in the interbasaltic beds,8 and in his “ Letter on Zeolite and Ochre”/] denies that the ochres are tuffs, and makes the important statement that “ we find this ochreous substance in its’ natural situation, in every inter- mediate stage between sound blue basalt, and ochre- red as miniurn ; and we see that the passage from one extreme to the other is by shades perfectly insensible.” On p. 15 he says, “ we frequently find specimens composed of sound basalt and ochre mixed.” But he does not like to assign the change to any specified cause, or to assert that it is still in progress. i Sir R. GrifflthT[ made an import,ant step in the discussion in 1836. At the Bull’s Eye, Glenarm Park, he came upon “ ochreous strata,” which he referred to the alteration of quite anot,her type of igneous rock than the. basalts of the area. He observes that they “ occasionally contain small crystals of quartz in double six-pided pyramids, and bear a strong resemblance to the decomposed clay porphyry of Sandy Bream.” He held that “ the ochre-beds probably originated in the projection of volcanic as;hes from a submarine volcano, and the clay beds, sandstone, alld wood coal were deposited among them at the bottom of the sea during the interval of the great eruptions of perfectly fllsed lava.” Agreeing probably with Hamilton’s suggestion that igneous alteration should be invoked, Griffith (p. 159) regarded the lithomarge beds of the Giant’s Causeway area as fused or partially fused representatives of the Sandy Braes porphyry, which he rightly placed in the interbasaltic zone. Here, then, a certain confusion was set up by the introduction of new and singularly acute ideas. J. E. Portlock ** wisely disregarded, or remained unaware of, Griffith’s suggestion of, a rhyolitic origin for the red zone on the Causeway cliffs. He * “ Letters concerning the Northern Coast of the County of Antrim ” (1790), Letter V. -8 ; ; (9). t “ Account of the Peninsula of Portrush ” Pamphlet, n.d. Newry (?),1815 $ “ Inquiry into the consistency of Dr. Hutton’s Theory,” etc., Trans. R. Irish Acad., vol. ix. (1803), p. 458. . . . . 9 “ On the Alterations in the Structure of Rocks,” etc., Phil. Trans., 1808, ~13. 195 and 200. 11I G‘J. Dubourdieu, “ Statistical Survey of the County of Antrim ” (1812), Appendix I., p. 11. 11A ddress, Journ. G. S. Dublin, vol. i., p. 158. ** “ Report on the Geol. of Londonderry,” etc., Ordnance Sur;ey, 1843.