482 R. HARKNESS AND H. A. NICHOLSON ON THE STRATA BETWEEN 



the rocks are, in part, well exhibited. Their nature and arrange- 

 ment have been described by the officers of the Irish Geological 

 Survey (description of Map 35, NJ3.). The hill of Grange, where 

 these rocks are best seen, consists principally of porphyries, traps, 

 and ashes, the latter at one spot affording abundance of fossils of 

 Bala age. The porphyries have a great affinity to those of Portraine 

 and Lambay ; and the traps and ashes are intimately related to those 

 of the east coast of Ireland. 



The western side of the hill of Grange consists of Coniston Lime- 

 stone, well seen in the portion of the hill known as " the Chair of 

 Kildare " and its immediate surroundings. Judging from its strike, 

 this limestone would appear to be brought against the underlying 

 igneous rocks by means of a fault. Although the limestone and 

 igneous rocks are well exposed, the strata which overlie the former 

 cannot be recognized in the hill of Grange. 



Though provided with the six-inch Map, on which Mr. Du Noyer 

 recorded his observations, through the kindness of Prof. Hull and 

 Mr. O'Kelly of the Irish Geological Survey, the rocks succeeding the 

 limestone could not be determined by us. The occurrence of dark 

 shales about this position was indicated on the Map, but the places 

 where they are represented no longer show them. 



The exposures seem to have been in ditches ; and they are now 

 covered up. On the west the Coniston Limestone is cut off by a 

 fault, " the last traces of it being seen on the south-west brow of the 

 Chair hill." 



A short distance south-west of the Chair, a hill called Dunmury 

 occurs. The composition of this hill is altogether different from 

 that of the hill of Grange, neither limestone nor volcanic products 

 being found in connexion with it. 



On the eastern side of this hill, and on the western side of the 

 road to Kildare, near a well, a very dark- coloured compact rock, 

 exceedingly like the Graptolitic Mudstones, is seen ; and rocks of a 

 like nature occur westward. 



The exposures of rock on this hill, however, are very poor ; Mr. 

 Du Noyer records, on the map, the appearance of purple and greeu 

 rocks on the west of the road south of the well above referred to. 

 These cannot now be seen ; and it is probable they were exposed 

 when the surface of the road was levelled. Judging from Mr. 

 Du Noyer's observations, these purple and green rocks appear to be 

 nearly akin to the Knock beds. Should this be the case, and taken in 

 connexion with the occurrence near them of strata resembling the 

 Graptolitic Mudstones. it would seem that the rocks of Dunmury 

 hill represent these two series. 



It is also to be remarked that the outline of this hill differs greatly 

 from that of the hill of Grange. 



The contour of Dunmury bears a much greater affinity to the hills 

 of the north-west of England composed of rocks above the Borrow - 

 dale series than to such as are made up of members of this portion 

 of the Bala group. 



