HARD Wl CKES S CIENCE - G O SSIP. 



179 



s phere situated in nearly the same parallel of latitude 

 e.g., Malta and Bermuda. 



The following table shows the average mean 

 monthly temperature of several years past : — 



January 

 February 

 March 

 April ... 

 May . . . 

 June ... 



40 Fah. 

 42° ,, 

 5o° „ 

 58° „ 

 69° „ 

 76° „ 



July ... . 

 August 

 September 

 October 

 November . 

 December . 



°3 

 83' 



67 



55 

 47 



Fah. 



>) 



During the recent winter there has been at least 

 ten days continuous skating, and the thermometer 

 during the month of January was frequently below 

 20 Fah. or 12 below the freezing-point. During the 

 last six months there has been an extreme range of 

 82 , i.e. from 99 to 17°. 



This subject is well worthy of enlargement and 

 development, but meantime this is perhaps enough 

 for Gossip. 



SKETCH OF THE GEOLOGY OF DUBLIN 

 AND WICKLOW. 



By Wm, Hellier Baily, F.L.S., F.G.S., 

 M.R.I. A., &c. 



THE metropolis of Ireland is most favourably 

 situated with regard to its position, its eastern 

 extremity being bounded by the sea, to the north- 

 east the peninsula of Howth forms the limit of 

 Dublin Bay in that direction, to the south that of 

 Kingstown and Dalkey ; south of Dublin the granite 

 range of mountains are a conspicuous feature in the 

 landscape. 



Of the igneous rocks, granite, the most important, 

 is well displayed near Dublin, commencing about 

 three miles south, extending in a south-westerly 

 direction for a distance of twenty-nine miles to near 

 New Ross, in the county of Wexford, with an average 

 width of eight or ten miles, and a maximum, at one 

 part, of eighteen miles. It forms the Dublin moun- 

 tains, rising to an elevation of 1,763 feet from the 

 sea-level, above the Three Rock Mountain at Fairy 

 Castle. The lower hills, near the sea-coast, such as 

 that of Killiney, are 480 feet, and Dalkey 472 feet, 

 in height. The outline of this range shows a suc- 

 cession of gently-undulating and rounded eminences, 

 descending more rapidly towards the sea. 



In the adjoining county of Wicklow the mountains 

 rise to a greater height ; Lugnaquillia, in the southern 

 part of the county, being the highest, is 3,040 feet 

 elevation, consisting of a mass of mica schist resting 

 on the granite ; all the loftiest parts of the adjacent 

 mountains are also composed of mica schist. 



The granite may be seen along the coast from 

 Blackrock, south of Dublin, to Kingstown and 

 Dalkey ; from the latter place it has a superficial 



breadth of about eight miles. From the quarries at 

 Dalkey Hill was obtained the stone used in the con- 

 struction of the harbour and piers at Kingstown, 

 about 6,000,000 tons being used in the formation 

 of the two breakwaters. A large quarry in the town 

 of Kingstown was also extensively worked for mate- 

 rial used in the construction of the harbour and 

 piers at Kingstown ; other quarries have been 

 opened on the eastern side of the Three Rock 

 Mountain for supplying stone for building purposes 

 and for flagging. 



The Killiney and Dalkey granite is coarsely 

 crystalline, varying somewhat, however, in different 

 places. The Rev. Dr. Haughton, F.R.S., &c, has 

 fully described the Dublin and Wicklow granites in a 

 memoir of the Lower Palaeozoic and associated Igneous 

 rocks of the south-east of Ireland. ("Trans. 

 Royal Irish Acad.," vol. xxiii., 1859, pp. 564, &c.) 

 Veins of a closer and whiter texture, in which the 

 mica is scarcely or not at all perceptible, are fre- 

 quently found to traverse the granite of this district ; 

 it is called Enrite, and is evidently intrusive ; occa- 

 sionally it assumes larger dimensions than that of 

 mere veins. Black mica (Lepidomelane) is not 

 uncommon in this granite ; a remarkable plumose 

 variety of white mica (Margarodite) has been found 

 at Ballybrack. In the Dalkey quarries it is not 

 unusual to find perfectly-formed crystals of black 

 quartz in the joints ; fine crystals of Tourmaline 

 are also occasionally met with in the granite of 

 Dalkey, and the mineral called Killinite, from its 

 having been found in the granite of Killiney and also 

 at Dalkey. 



Metamorphic Rocks. — Mica schist, or altered 

 Lower Silurian slates, these again blending into 

 unaltered Lower Silurians, flank the granite from a 

 point near Killiney to near New Ross, in the county 

 of Wexford, spreading out, as shown on the southern 

 boundary of sheet 121 of the Geological Survey maps 

 to a breadth of over four miles. The junction of the 

 Granite and Metamorphosed Slates is clearly observ- 

 able along the sea-shore under Killiney Hill, at 

 Roche's Hill, and to the west of Killiney Park ; in 

 the road and railway cuttings of the neighbourhood ; 

 as well as their metamorphism into mica schist, which 

 often contains crystals of chiastolite. 



The manner in which the granite has been forced 

 into the slates, penetrating them in wedge-shaped 

 masses and veins, may be observed on the shore at 

 this place. From the Killiney Hills a fine view of 

 the Bay of Dublin, with Howth to the north and 

 Bray Head south, may be seen. 



The Scalp, about two miles north of Enniskerry, 

 and about three miles south of Carrickmines station, 

 on the Dublin, Wicklow, and Wexford Railway, is a 

 picturesque pass, the granitic rocks showing great 

 erosion ; its junction with the mica schist may be 

 readily observed. 



In the glen of the river Dargle, near Enniskerry 



