Sngarloaf 

 su>untains> 



Contact of 



graniie with 

 M:!cuinb«nt 



tacks. 



Socks t^ the 

 «r»p family. 



^'anfriM of 

 limestone. 



GEi^id^T o'r THiJ yiciNiry or dubi.i»» , 



The corneal masses ofthe Sugar-loaf mouutains, with th«- 

 sumtutts of Brayhead, and Shankbill, resembling them in 

 structure, are composed of quartz ; and it may be remark- 

 ed, that the conical form appears to be in some measure 

 c1>aracteristic of mountains composed of this substance ; for 

 Mr. Jameson informs me, that he has seen in Lusatia de« 

 tached conical summits composed of it ; and that the well 

 known Paps of Jura, ai)d the conical summits in the moun- 

 tains separating Caithness from Sutherland, are of the same 

 material ; as also is, according to Dr.Uerger, the mountain 

 Diirnhill, near the town of Portsoy*. 



The actual contact of granite with incumbent rocks has 

 been observed at the following places in the counties of 

 Dublin and Wicklow. On the western side of the granite, 

 in a stream let joining the Dodder, west of the glen above 

 Billinascorney ; at Golden hill, near the granite quarries ; 

 and at Kilranelagh : on the eastern side, at Killiney ; at the 

 southern extremity of the Scalp ; at Tonelagee ; near 

 Aghavana^h to the eastward ; and at the south-western side 

 of Croghon Kinshela. On the shore of Dublin bay, between 

 Booterstown and Blackrock, a mass of compact limestone 

 is visible within a few fathoms of the granite* but in the in- 

 terval the rock is concealed. 



Near Ballinascorney, on the western verge of the granitic 

 mountains nearest to Dublin, rocks of the trap family oc- 

 cur; and thence to the south-westward, along the bor* 

 ders of the counties of Wicklow and Kildare, various inter- 

 nafediate rocks between the granitic tract above mentioned 

 ^nd the limestone of the flat country to the westward will be 

 found. At Arklow rock, on the south-eastern extremity of 

 the county of Wicklow,' columnar rocks of the trap family 

 have been observed by Dr. Wollaston and the Rev. Dr, 

 Brinkley. 



The quarries in the more immediate neighbourhood of the 

 city afford many varieties of calcareous productions, Th*f 



Vast, thickness * Humboldt states, that in South America, quartz constitutes, ex« 

 ff quartz. clusivcly, a mass of more than nine thousand five hundred feet in thicl?. 



ness, which he considers as of a ** formation" peculiar to the Andes. 



He has not mentioned the form of the summits: Tableau Phys. 



p, 128. . 



calp 



