310 Geological Stnicture of the Vicinity of Duhlin, 



some interest in a geological view, from the great extent of* 

 the space occupied by limcslone ia several o? the counties 

 near Dublin. 



At the peninsula of Howth, which forms the southern 

 side of Dublin Bay, grey ore of manganese, and brown 

 ironstone (Museum of Dublin ColUge, Nos. 1067-8. b87.) 

 have been obtained in considerable quantity : and a variety 

 of the earthy-black-cobalt-ore of VV'erner has been found 

 by Mr. Stephens and Dr. Stokes at the south west side of 

 the hill, in the form of a coating of a rich blue colour^ which 

 incrusts the fissures of a rock of slate clay, nearly ap- 

 proaching to whetslate (Museum of Dublin College, 

 No. 267) : Mr. Tennaut has in this substance ascertained the 

 presence of the oxides of cobalt and of manganese; and the 

 discovery of it is iniportant, as it indicates the probabilitv 

 of (he existence of other more valuable ores of cobalt in 

 that utiahbourhood. 



The heights of very few of the mountains near Duhlin 

 have hitherto been measured : the onlv published ob- 

 servation with which I am acquainted, being that given 

 in a section annexed to the report on the Gold-mine by 

 Messrs. Mills and Weaver already referred to ; where the 

 summit of the mountain Croghan Kinshela is staled to be 

 2012 feet above the river at Kilcarragh bridge, which is 

 about four miles from the sea. I have nwself ascertained 

 by the barometer the heights of the following places in the 

 county of Wicklow, above the house of Mr. Greene, at 

 Kilranelagh, viz. — 



Feet. 



Lugnaqu'dla, supposed to be the highest mountain 



of the county ■. 2435" 1 



Cadeen^ a mountain detached from the rest, and a 

 conspicuous object from the adjacent flat coun- 

 try 1 55S-9 



Baltin glass- hill 68 1 -8 



Eadestown-hill 749-4 



Brusselstoirn-liill 740* I 



Kilranelagh-hill 705-5* 



* The first three heights above mi ntioncJ, are each the mean of three 

 observations, llie rest arc Irom single observiitiona with two c-xceileiit ba- 

 rometers. Mi-. Greene's house is (by a single observation) 95,08 feet above 

 the level of the crosf roads at the bridge of Tia.'cmiU, a little village on the 

 river Slaney, the elevation of which above the sea will be very well sup- 

 plied, when a branch of the Grand-canal shall be extended in this direction, 

 a.6 13 now intended. The distance of 'I'uckmill fro'Vi the sea in a direct line 

 is about eiohiecn Enrlish raiJes. 



Of 



