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III. 



THE CARBONIFEROUS VOLCANOES OF PHILIPSTOWN IN 



KING'S COUNTY. 



By W. D. HAIGH, B.A, B.Sc, A.R.C.Sc.I, 

 Demonstrator in Geology at the Royal College of Science for Ireland. 



[Read April 27. Published Jul* 2, 1914.] 



About three miles to the north of Philipstown in King's County and close to 

 the boundary of Meath, a number of small hills rise from the great central 

 limestone plain and form a conspicuous feature over a very large area of this 

 part of the country. 



The chief of these is Croghan Hill, which, on approaching it from the 

 south, stands out as a conical eminence rising with steep grassy slopes to a 

 height of 769 feet above sea-level, and about 460 feet above the general level 

 of the plain. It slopes more gently to the north for three-quarters of a mile 

 before descending somewhat abruptly to the level of the plain beyond, and 

 forms a pleasing contrast to the great area of brown bog-land which surrounds 

 it. This forms a centre round which a group of minor hills are clustered, 

 the whole occupying an area of approximately four square miles. 



On reference to the one-inch Geological Survey map 1 of the district, it 

 will be observed that the area is mapped as greenstone (diorite) and green- 

 stone ash ; and these rocks with a few bands of limestone extend over the 

 greater part of the area. In the explanatory memoir of the district, 2 the 

 greenstones are treated as intrusive; but the greenstone ash seems to be 

 regarded as interstratified in the Carboniferous limestone, although, as is 

 pointed out in the memoir, there is no direct proof of this, owing to the lack 

 of a continuous section. 



There are two main outcrops of these igneous rocks, separated from each 

 other by a band of limestone. One includes Croghan Hill and the surround- 

 ing district to the south and east, while the other lies to the west and extends 

 northwards, as a crescent-shaped band, round the base of the hill. A smaller 



1 GeoL Surv. Ireland : Sheets 109 and 110. 



2 Geol. Surv. Ireland : Explanations to sheets 98, 99, 108 and 109, 1865, p. 18. 



E.I. A. PBOC, VOL. XXXII., SECT. B. [-D] 



