Vol. 52.] 



ON" THE KILDARE IXLIER. 



501 



8 <^R 



and slates above the igneous rocks or in the ashes below them. 

 The igneous rocks are therefore almost certainly contemporaneous, 

 and this view is confirmed by an examination of their structure 

 both in the field and under the microscope. We shall describe 

 these rocks in a later part of this paper. 



At the western end of Grange Hill is the Chair of Kildare, where 

 the rocks are markedly different from those forming the main mass of 

 Grange Hill. The lowest bed seen is an ash-band continuous with 

 that which lies immediately below the lavas of Grange Hill. This 

 ash is exposed in the lane leading north-east to Grange Hill House, 

 and between this lane and the Chair no more rocks are seen in situ. 

 This tract of country is, however, in the direct line of strike of the 

 lavas of Grange Hill ; and it seemed 

 at first as if we had evidence of their «*•££ 



extension to this point, from the 2 



occurrence of a small quarry exposing 

 numerous blocks of lava which were 

 apparently taken to be in situ by the 

 officers of the Geological Survey. After 

 some consideration, however, we came 

 to the conclusion that these blocks were 

 not in place, and that although the 

 lavas probably do extend to this point 

 we have no proof of their doing so. 



The limestone of the Chair appa- 

 rently forms one main mass and several 

 smaller lenticular masses, separated one 

 from another by tracts of country which 

 generally show no exposures and are 

 probably occupied by shales. Sections 

 show that the microscopic characters 

 of the limestone do not vary much in 

 different parts, for everywhere the rock 

 is partly horny, partly crystalline, 

 being formed of well- cleaved plates of 

 calcite. We divide the limestone into 

 four bands, A, B, C, and D, of the same 

 general age. 



The succession of the limestone- 

 bands is shown on p. 592, but the 

 thicknesses given for the various beds 

 are only approximate, it being scarcely 

 possible to measure them accurately 

 owing to the difficulty in ascertaining 

 the dip. The limestone, however, 

 has the normal north-east and south- 

 westerly strike of all the beds of Grange Hill, and it dips south- 

 east at a rather high angle. The lowest beds are seen at the foot 

 of the Chair. Taking 50° as the average dip, we have the following 

 section at the top : — 



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