Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/568

482 the rocks are, in part, well exhibited. Their nature and arrangement have been described by the officers of the Irish Geological Survey (description of Map 35, N.E.). 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 Limestone, 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 Borrowdale series than to such as are made up of members of this portion of the Bala group.