Geological Relations of the East of Ireland \ 181 
§ 72. Tara hill, (see PI. 8. No. 7.) appears to be an analogous 
mass, composed principally of felspar porphyry embodied in clay 
slate \ but its structure is by no means well exposed. It presents a 
rugged aspect, craggy rocks protruding above the loose stones 
which cover the greater part of its surface. The great body of the 
hill consists of porphyry, with a compact felspar base, that some 1 * 
times passes into hornstone, containing inlaid crystals of glassy 
felspar; but greenstone also appears occasionally. Through the 
felspar base the matter of hornblende seems to be diffused, its usual 
colour being bluish grey of various shades, and hornblende itself 
also appealing sometimes in indistinct spots : but this stone assumes 
various colours according to its relative state of disintegration ; 
white, yellow, red, and brown, the shade of colour being lightest 
next the surface. In every stage of decomposition, however, it is 
the base only that is affected, the crystals of glassy felspar retaining 
their form and splendent lustre. Tara hill commands an extensive 
view of the eastern portions of the counties of Wicklow and Wex- 
ford. 
§ 73. The county of Wexford may be generally described as 
consisting of high land, declining in undulating swells from the 
granite chain on the west toward the Slaney and the Bann ; again 
rising on the east from these rivers into high ground, which de- 
scends toward the coast. Chains nearly parallel are thus formed, 
which affect a north-east and south-west disposition, as the Conna 
range (part of which is in the county of Wicklow), the Slieve 
Buy, and Bree hill ranges, the last in its extremities exhibiting 
isolated hills. The most southern range is that of Forth, which 
constitutes a rugged rocky ridge, about five or six miles in length, 
elevated about 500 feet above the sea, and consisting almost en- 
tirely of quartz rock, which, however, has a tendency to the slaty 
