•«BOt<JGY OF THR VICINITY OF DITBLtlT* 283 



i?atp of Mr,, Klcwan, a variety of limestone, of which an ex- 

 cellent description and analytii^ have been published by Mr. 

 Knox*, is the prevailing rotk. Brown-spar (Jameson) is 

 found in veins at the quarries near Dolphinsbarn ; and beds 

 of magnesian limestone were observed by Mr. Stephens in 

 the bed of the river Dodder, at Miltown, and at Classons- 

 bridge, above that place. The petH factions, which abound 

 itn inaiiy parts of this limestone country, the calp, and tlie 

 beds of magnesian limestone afford some of the features 

 which may assist in deciding on the " formation" of Werner, 

 to which it is to be referred ; a point of considerable interest, 

 from the great extent which the limestone occupies in the 

 counties of Dublin, Kildare, and Carlow. 



In the peninsula of Howth, which forms the northern side Ora. 

 of Dublin bay, gray ore of manganese with brown iron-stone, 

 and brown iron-ore (Museum of Dublin College, Nos, 

 IOC7-8, 887.) have been obtained in considerable quantity : 

 and a variety of the earthy black cobalt ore of Werner has 

 been found by Mr. Stephens and Dr. Stokes on the southern 

 Bide of the hill, forming a crust of a rich blue colour lining 

 the fissures of a rock of slate clay nearly approaching to whet-i 

 slate, (Mus. T. C. D. No. 267) : Mr. Tennant has in this 

 substance ascertained the presence of the oxides of cobalt 

 and of manganese ', and the discovery of it is important, a«( 

 it indicates the probability of the existence of other more 

 valuable ores of cobalt in that neighbourhood, Lugnaquilla, 

 which is supposed to be the highest oT the Wicklow moun- 

 tains, is situate to the south-westward of the centre of thq 

 mountainous district : I have found it, by the barometer, to 

 be 2455'! feet above the hftuse of Mr. Greene at Kilrane- Heights. 

 lagh> which is itself consideiably elevated above the sea. 

 Cadeen, a hill detached from the body of the liiountains, 

 and forming a striking object from the adjacent flat coun- 

 try, i« 1558.9 feet; Baltinglasshill, 631.8 feet ; Eadestown, 

 749«4 feet; Brusselstown, 740.1 feet; Kvlraneiagh hill, 

 705*5 feet above the same placef. Of 



■ ■• T'rahfactions of ihe Roy. Irish Acad', vol. VIII, p. 207. 

 ' -f The first three heights cbove mentioned are each the mean of three 

 tibserTatibrfs, the rest are from single observations, with two excellent 

 barometers. Mr. Greene'? house is (by a single observation) 95-08 feet 

 '• ' above 



