182 



HARD WI CKE 'S S CI EN CE-GO SSI P. 



vertically through the beds ; others as tracks 

 running along the surface. Larger tubular casts 

 passing vertically through the beds have been de- 

 scribed by the late Dr. Kinahan as Histioderma 

 Hibemicum. 



At the top of the hill in Kilruddery demesne, be- 

 longing to the Earl of Meath, the surfaces of the 

 quartz rock, associated with the Cambrian formation, 

 are distinctly rounded and scored by glacial action. 



The Dublin, Wicklow, 

 and Wexford Railway is con- 

 structed through this mass 

 of rocks at Bray Head by a 

 series of short tunnels and 

 cuttings, and by bridges or 

 viaducts, exposing sections 

 of strata and exhibiting 

 various geological pheno- 

 mena. 



The Lower Silurian rocks, 

 south of Dublin, are only 

 fossiliferous at a few locali- 

 ties ; near Rathdrum, in the 

 county of Wicklow, at Slie- 

 veroe, are strata of Caradoc 

 Bala age, from which have 

 been obtained the following 

 characteristic fossils : — Fa- 

 vosites fibrosus, Orthis testn- 

 dinaria, 0. actonite, Leptizna 

 sericea, and Euomfhalus per- 

 turbatus ; the Trilobites 

 Calymene Blumenbachii, Ho- 

 molonotns bisulcatus, Trinn- 

 dens concentrkus, and Bey- 

 richia complanata. 



Cambrian strata are also 

 the prevalent rocks on the 

 peninsula of Howth, county 

 of Dublin ; they are asso- 

 ciated with quartz rock, as at 

 Bray. The 'rocks here are 

 more slaty in composition, 

 and the presence of Old- 

 hamia is rare ; the late 

 Professor Kinahan believed 

 he had discovered it in 

 what are called the " Puckrocks," on the shore 

 east of Howth, accompanied by tracks, resembling 

 those observed at Bray; the highest point, Ben 

 Howth, is 560 feet high. In the demesne of the 

 Earl of Howth these rocks are well seen, and a 

 picturesque view may be obtained of the island of 

 Ireland's Eye, which is composed of similar strata, 

 Cambrian and quartz rock. In the further distance 

 may be seen the island of Lambay. The drift at 

 Howth, in the cliffs over Balscadden Bay, is of consi- 

 derable thickness, containing fragments of marine 

 shells. On the Dublin mountains, at an elevation of 



»w 



Fig. 129. Large Tubular 

 cast of Histioderma 

 Hibemicum. 



more than a thousand feel, marine shells have been 

 collected and described by the Rev. Maxwell Close 

 from two places ("On the Elevated Shell-bearing 

 Gravels near Dublin," Jonni. Gcol. Soc. of Dublin, 

 vol. iv., New Series, p. 36). At Bohernabreena, near 

 the river Dodder, beyond Fort Bridge, about six miles 

 S.W. of Dublin, marine fossils were also obtained 

 from the drift-gravel and sand by the late Dr. Kina- 

 han [Journ. Gcol. Soc. of Dublin, vol. viii. p. 87). 



The formation upon which Dublin is built, and its 

 immediate neighbourhood, is Upper Limestone ; this 

 formation, however, being for the most part covered 

 by drift, composed of sand and gravel. 



Sections in railway cuttings, rivers, and canals, 

 and various quarries, show the character of the rock 

 to be a, dark earthy limestone, technically termed 

 calp ; fossils in this rock are comparatively rare. 

 The Lower Carboniferous Limestone appears at 

 Raheny, continuing to Howth, where it is more 

 fossiliferous. At Balscadden Bay, north-east of 

 Howth, Lower Limestone shale, similar to the rocks 

 forming the low cliffs on shore a little south of Mala- 

 hide, may be seen. It rests unconformably on Cam- 

 brian strata, containing numerous corals, crinoids, 

 brachiopods, Sec. 



The Limestone at Howth is compact and thick- 

 bedded, frequently magnesian, and occasionally as- 

 suming a perfect dolomite. 



The picturesque scenery of Howth (reached by a 

 branch of the Great Northern Railway from Amiens- 

 street terminus), is of considerable interest, especially 

 where seen from the road round the east cliff, and 

 through the Earl of Howth's demesne, the more 

 elevated parts (towards the Baily Lighthouse) being 

 nearly as wild in character as some parts of Connemara. 



The rocks forming the low cliffs on the shore 

 south of Malahide, Lower Limestone shale, contain 

 an abundance of fossils, corals, crinoids, and mol- 

 lusca, especially brachiopoda. On the surface of 

 some of the beds, where weathered by sea and atmo- 

 spheric action, the characteristic coral, Lithodcndroii 

 junceum, may be seen in bunches attached to a large 

 bivalve shell, which was named by Professor McCoy 

 Pleurorhynchus fusifonnis. The quarries of Lower 

 Limestone near Malahide, at Feltrim, a little to the 

 south-west, and Sea Mount, south-east, has supplied 

 a large number of species. 



Still farther north, at Portraine, reached by the 

 same railway from Donabate station, eleven and a 

 quarter miles from Dublin, the prominent rocks are 

 Lower Silurian, of Caradoc Bala age, similar strata 

 also occurring at the Island of Lambay, two and a 

 half miles east. 



The beautiful ro'ck called Lambay Porphyry, which 

 forms a large proportion of the Island, composed of 

 pale green crystals of orthose felspar, in a base of 

 a dark green colour, also occurs on the opposite Por- 

 traine coast. 



The Lower Silurian Limestone on this coast, as at 



