HARDWICKE'S SCI EN CE- GOSSIP. 



169 



SKETCH OF THE 

 GEOLOGY OF BELFAST AND THE NEIGHBOURHOOD. 



By W. H. BAILY, F.L.S., E.G.S., &c. 



Palaeontologist to the Irish Geological Survey. 



ELFAST ;is situated on the Upper 

 New Hed Sandstone, "Bunter," 

 and is covered by alluvium on the 

 eastern side, being bounded by the 

 river Legan ; a higher division of 

 the Triassic, or New Bed Sand- 

 stone formation, consisting of red 

 marls and sandstone, " Keuper," 

 also extends across the country, 

 i having the cretaceous rocks as its 

 boundary in a south-westerly direction. 

 One of the nearest geological places 

 of interest in the neighbourhood of 

 Belfast is that of Cave Hill, in the 

 county Antrim, about two miles from 

 the extreme northern end of the town. 

 This hill, with other basaltic eminences 

 west and south-west of Belfast, such 

 as the Black Mountain, 1,272 feet in 

 height, Black Hill, 1,884, and White Mountain, 820 

 feet high, present very prominent features in the 

 landscape ; their eastern slopes are rugged and pre- 

 cipitous towards the north, but more gradual and 

 easier of ascent to the southward. 



The basaltic plateau of the north-east of Ireland, 

 of which this district forms a part, has been de- 

 scribed by the late General Portlock in his Geo- 

 logical Report on Londonderry, Tyrone, &c. ; its 

 thickness on these hills ranges from 424 to 817 feet. 

 Alternations of mineral character have been observed 

 in these volcanic rocks, which indicate successive 

 flows, with intervening periods of repose. 



These hills form the escarpment of the Chalk and 

 Greensand; sections of these sedimentary strata 

 (which are sometimes penetrated by the basalt in 

 the form of dykes), as well as of the Lower Lias, or 

 Bhffitic beds, are well exposed at Cave Hill. The 

 quarries in the Upper Chalk " White Limestone " 

 No. IIG. 



are extensive; the stone being largely used for 

 lime, is conveyed by special tramway to Belfast. 



At Collin Glen, in the same county, five miles 

 south-west of Belfast, a deep ravine cut by the 

 Collin river exposes similar strata, the upper 

 cretaceous rocks resting immediately upon the dark 

 grey or bluish shales of the Lower Lias, or Ilh?etic 

 beds, under which are the marls of the Keuper 

 division of the New Red Sandstone. The section 

 at this place has been described by Mr. Ralph Tate, 

 F.G.S. {Quart. Journ. Geol. Soc, vol. xx. p. 103), 

 and also by the Geological Surveyors in the Expla- 

 nation to Map 36, " Geological Survey of Ireland." 



The strata being displaced by several faults, the 

 section exhibited is a very instructive one, with an 

 abundance of fossils in some of the beds. 



The oldest rocks are the Keuper marls, the upper- 

 most division of the New Red Sandstone, upon 

 which the Rhgetic beds have been deposited, con- 

 sisting of shales and thin bands of limestone, some 

 of them full of characteristic fossil shells, such as 

 Avicula contorta, Cardium Rhaticiim, &c. 



On these rest what Mr. Tate designates as the 

 " Hibernian Sandstone," which he groups into three 

 zones, the lowest, or "Glauconitic Sands," con- 

 taining Exogyra conica in profusion, a shell belong- 

 ing to the Ostreoid group ; the middle division 

 consists of "yellow sands and marls," with 

 shells, &c., amongst which Peden quinquecostcttus 

 is the most prevalent ; and the upper, upon which 

 the Chalk rests, is " Chloritic Sandstone," locally 

 termed "MuUatto;" in the beds of this division 

 another species of Ostreoid shell, Exogyra columba, 

 is plentiful, with numerous remains of sponges, 

 resembling Siphonia of the Warminster Greensand. 



At Woodburn Glen, two miles north-west of 

 Carrickfergus, similar strata are to be seen, cut 

 through by the Woodburn river. 



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