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EXPLANATORYMEMOIR TO ACCOMPANY SHEETS 49, 50, AND PART OF 61 OF THE MAPS GEOLOGICALSURVEY OF IRELAND, INCLUDING THE COUNTRY AROUND DOWNPATRICK, AND THE SHORES OF DUNDR’UM BAY AND STRANGFORD LOUGH, COUNTY OF DOWN, . BY W. A. TRAILL, B.A., F.R.G.S.I., AND F. W. EGAN, B.A. .hbhbhed by Order of the Lords Commissiorzers of Her Majesty’s I'reaswy. DUBLIN: PRINTED FOR HER MAJESTY’S STATIONERY OFFICE : PUBLISHED BY ALEXANDER THOM, 87 & 88, ABBEYcSTREET”; HODGES, FOSTER, & CO., 104, GRAFTON-STREET. LONDON: LONGMANS, GREEN, READER, AND DYER* 1871. LIBT OF ILLUSTRATIQNS. w ’ Page Felstone Dyte, at Kearney Point, Ards, . 2 Fossils, . 23 Felstone Dyke, at Kearnep Point, Ards, . , 41 Contorted Strata, on Shell Hill, . 47 Basalt Dykes, of different ages, . * 57 Section along coast, south of Killough, . 60 THE GEOLOGICALSURVEY OF THE UNITEDKINGDODZ 18 CONDUCTEDUNDERTEEPOWERSOFTEE STH & 9m VICT., CHAP. 63.-31~~ JULY, 1845. DIRECTOR-GENERALOPTHE GEOLOGICALSURVEYOPTHEUNITEDKINGDOM: SIR RODERICK IMPEY MURCHISON, BART., K.&B., D.C.L.,F.R.S.,&C., 8.X. Geological Survey Ofice am3 Mzlseum of Practical Geology, Jerlrtyn.dl’dtt, L~ddb. IRISH BitANGEl. Ofice, 14, Hume-atreet, Dublin. DIRECTOR: EDWARD HULL, M.A.,F.R.S., F.G.d. DISTRICT SURVEYOR: G. H. KINAHAN, M.R.I.A.,&c. GEOLOGISTS: W. H. BAILY, F.G.s.,L.S. (Acting Pal&bntologiat); 3. @KELLY, M.A.,H.R,I.~; R. G. SYMES, F.G.8.i J. L. WARREN, B.A. ASSISTANTOEOLOUISTS: 8. B, N. WILKINSON; J. NOLAN, F.R.G.S,I.; W. B. LEONARD; H. LEONARD, M.R.I.A.;R. J. CRUISE, M.R.I.A.; W, A. TRAILL, B.A.; F. W. EGAN, B.A.: E. T. HARDMAN,F.R.a.S.I. W. E. L’E. DUFFIN, B.A. FOSSIL COLLECTORS: ALEX. M’HENRY; EDWARD LEESON. The observations made in the course of the Geological Survey are entered, in the first instance, on the Maps of the Ordnance Townland Survey, which are on the scale of six inches to the mile. By means of marks, writing, and colours, the nature, extent, direction, and geological formation of all portions of rock visible at the surface are laid down on these maps, which are preserved as data maps and geological records in the of&e in Dublin. The results of the Survey are published by means of coloured copies of the one-inch map of the Ordnance Survey, accompanied by printed Explanatory Memoirs. Longitudinal sections, on the scale of six inches to the mile, and vertical sections of coal-pita, &c., on the scale of forty feet to the inch, are also published, and in pre- paration. Condensed memoirs on particular districts will also eventually appear. The heights mentioned in these explanations are all taken from the Ordnance Maps, AGENTSPORTHE SALE OFTHE MAPSAND PUBLICATIONS: Messre. LONGMANS,GREEN, & Co., London ; Messrs. HODGES,FOSTER, & Co., Grafton-street, Dublin; ALEXANDER THOM,Printer and Publisher, Abbey-street, Dublin. PREFACE. THIS District was surveyed by Mr. W. A. Traill, and Mr. F. W. Egan, under the direction of the late Professor Jukes, assisted by Mr. Du Noyer, then District Surveyor. Mr. Egan examined that portion of Sheet 49 lying to the west of the meridian of Ddwn- patrick, Mr. Trail1 that portion lying to the east of the same line, together with Sheets 50 and 61. Having last year gone carefully over the coast secti?ms along the shore of Dundrum Bay with Mr. Tra,ill’s map in my hand, and seen the careful manner in which the basaltic dykes and other geological phenomena, of that portion of the district had been mapped, I feel satisfied that the larger portion to the northward has been worked by himself and his colleague with similar accu- racy, and can only regret that the smallness of the scale makes it impossible to show the minute details connected with the remarkable series of trap dykes which penetrate the rocks along the eastern coast, and the shores of Strangford Lough It is right, however, that I should state, that as the survey of the Downpatrick Sheet had been completed and inspected by my predecessor, Mr. Jukes, previous to my arrival in Ireland, I did not consider it necessary personally to examine the rocks of the Downpatrick Sheet, described in this Memoir. EDWARD HULL, Director of the Geological Survey of Ireland. Geological Survey Ofice, Dublin, March, 1871. EXPLANATORPMEMOIR SHEETS 49 AND 50, WITH THAT PORTION OF SHEET 61 THAT LIES TO THE NORTH’OF DUNDRUM BAY, OF THE M.IPY OF TIIE GEOLOGICALSURVEY OF IRELAND, GENERAL DESCRIPTION. THE district contained in these sheets, is situated wholly in the county Down, about midway between its extreme northern and c southern margins, and along its eastern shore. It embraces that portion of the county which lies in the neighbourhood of Down- patrick, that town occupying a nearly central position ; and ex- tends in an easterly direction from the town of Ballynahinch to the sea-coast, from a point about three miles N. of that town (in sheet 49) eastward to Ringboy Point, and southward to “ The Four Roads ” (in sheet 61), two miles W.N.W. of Dundrum ; from thence by a straight line to Dundrum Bridge, having for its southern boundary, Dundrum Bay. The whole district comprises an area of about 225 square miles. These maps include the southern extremity of the Ards Pro- montory, or part of that portion called “ The Upper Ards,” together with the two rocky islands off its eastern shore (in sheet SO), called the North and South Rocks, and the southern portion of Strangford Lough. The coast-line extends from Cloghy Bay on the north, to St. John’s Point on the south, and thence westward to Dundrum inner bay ; and also along the shores of Strangford , Lough, from. Ballyquintin Point to Long Island on the eastern, and from Killard Point to Pawle Island on the western side, mak- ing in all about fifty miles of *general coast-line, independent of the smaller bays and indentations. The principal places of note in this district are (in sheet 49) Downpatrick,* the county town ; Portaferry, Strangford, and Killyleagh on the shores of Strangford Lough ; Crossgar, Kilmore, Clough and Seaforde, inland ,* and the two small hamlets of Saul and Raholp to the N.E. of Downpatrick ; the town of Ballynahinch also lies partly within this sheet on its western margin. 8 In sheet 61, there are the following villages, Ardglass,” situated at the north-east corner of the sheet, in a small bajy on a very rocky shore, whose harbour is much exposed to storms from the eastward, being incommodious and rocky, It should be noted, that here, and along this part of the coast, the mean tide level is 8.64 feet above the Ordnance Survey Datum Plane (from which the heights are figured on the maps). At Ardglass Harbour, mean range of spring-tides is 15.43 feet, and of neap-tides, 8.03 feet. The magnetic variation here is 25O W., but decreasing 7’ annually.* The village of Killough, situated on the western side of Kil- lough Bay, which divides itself into Coneyisland Bay and Killough Harbour. The present harbour is simply a tidal one, but there are numerous natural advantages here for the formation of a harbour of refuge, with good, safe, and extensive anchorage. The “ Water Rock ” at the mouth of the bay, at present a most dangerous rock, is well suited for the formation of a break-water &fid quay, h&ving over $0 feet of water inside. l Dundrum, situated on the inner bay of that name, which latter is gradually getting silted up with sand and ttlluviu&, and is connected by a narrow channel between sand-hills or duties with the outer bay. 1. Form of the Ground. The physical features presented by this district may be gene- rally described as of a three-fold character ; either rugged and rocky tracts free from drift, or nearly so, such as that lying near the S.W. corner of sheet 49, and that extending in a north-easterly direction from Downpatrick, between that town and Strangford ; in the seoond place unevenly undulating tracts, also aearly free from dlift, and having the rock laid bare, some- times ta a large extent, or concealed nearly by a shallow covering of soil ; or thirdly, rounded elevations caused by the occurrence of moun& of drift, either isoiated, as is most frequently the case in the neighbourhood of Downpatrick and at the mouth of the River Quoile, or associated together with more or less uniformity ; together with those of an intermediate character, in all gradations, from the barren rock to the hill composed solely of drift. It is in the rocky and hilly re ion of which the southern boundary lim about two miles to t% e N. of Seaforde, neat the western margin of sheet 49, that the greatest ele+ations occur, the highest summit being that of Edendarriff MountainJ a rugged hill four and ti half miles S.S.E. of Ballynahinch. This point is 549 feet above the level of the sea, or about 200 feet above the flat * ” Ardglass,from a&--height, and glass-green, or ’ the Gre’en Height,’ was anciently the principal town of trade in Ulster (next to Carrickfergus) before the reign of, Queen Elizabeth, having become a place of cbnsiderable importance after the inv&Mi.” ‘though formerly a place of such iulportance and Ptrength, judging from the ruins of alx Anglo- Norman castles, it is now in a very back*ard &ate ; yet, still an exteti$ive fishery trade is carried on there in the summer.

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