TRANSACTIONS OF SECTION C. 527 



the same locality is at present unknown. But the Hesperornis and Ichthyornis from 

 the cretaceous beds of America possess veritable teeth, in the one case set in a 

 long groove in the jaw, and in the other iu actual sockets. Such intermediate, or, 

 as Professor Huxley would term them, intercalary forms, tend materially to bridge 

 over the gap which at first sight appears to exist between reptiles and birds, but 

 which to many palaeontologists was far from being impassable, long before the 

 discoveries just mentioned. The amphicoelous character of the vertebrae of 

 ichthyornis presents another most remarkable peculiarity, which is also of high 

 significance. I hear rumours of the discovery of another archceopteryx in the 

 Solenhofen Slates, which is said to present the head in a much more complete con- 

 dition than that in which it occurs on the magnificent slab now in the British 

 Museum. As yet, I believe, the jaws have not had the matrix removed from 

 them ; but should they prove to be armed with teeth, it will to me be a cause of 

 satisfaction rather than surprise, as confirming an opinion which some fifteen years 

 ago* I ventured to express, that this remarkable creature may have been endowed 

 with teeth, either in lieu of or combined with a beak. 



I must not, however, detain you longer with any of these general remarks, 

 which are, moreover, becoming somewhat egotistic, but will now proceed to the 

 business of this Section, in which I hope that more than one paper of great value 

 and interest will be forthcoming. 



The following Papers were read : — 



1. Sketch of the Geology of the Environs of Dublin. 

 By Professor E. Hull, F.R.S. 



2. On the Ancient Volcanic District of Slieve Guttion. By Joseph Nolan, 

 M.B.I.A., #*c, of H.M. Geological Survey of Ireland. 



Slieve Gullion is a somewhat isolated mountain situated some few miles north 

 of Dundalk, and west of the picturesque hilly country lying between the bays of 

 Dundalk and Oarlingford. The rocks which mainly compose it are massive dolerites 

 and elvanites, which have been erupted through granite of Lower Silurian a<*e. 

 From evidence obtained in a neighbouring locality, there is every reason to believe 

 that the period of this eruption was about the close of the Palaeozoic epoch. On 

 the west and south of the mountain the elvanite forms a remarkable dyke-like ridge, 

 when it changes in its character from a granitoid rock to a felstone porphyry. 

 Simultaneously with this change, suggesting conditions of less intense heat and 

 pressure, a remarkable fragmental rock makes its appearance. It is here almost 

 altogether composed of granite pieces ; so much so that it might be taken for a 

 disintegrating condition of that rock, but that the base is not crystalline. Its 

 mechanical character is confirmed on tracing the ridge further, where the granite 

 gives place to Silurian slates and grits. Here there is a mixture of slate and granite 

 fragments, and still further in the slate district it is almost altogether composed of 

 slate debris. At all these places the fragmental rock is intimately associated with, 

 the porphyry, so that where both are 'well exposed in sections it is impossible to 

 draw any line of demarcation between them, the lower part of the former gradually 

 acquiring the character of the latter, by the appearance in increasing quantity of 

 fragments of porphyry, until it ultimately passes into that rock. 



That we have here something analogous to volcanic agglomerate we can scarcely 

 entertain a doubt. Nevertheless, it differs very much from the usual type of that 

 rock, as it is, except in the deepest portions, mainly composed of pieces of non- 

 volcanic rocks, those pieces being of the crust through which the igneous mass was 

 protruded, and varying accordingly ; granite agglomerate prevailing in those portions 

 formerly occupied by that rock, a mixture of slate and granite near the boundary 

 of these formations, and slate fragments almost exclusively in the Silurian country 

 to the south-east. It is impossible to account for these phenomena by supposing 



* Nat. Hist. Rev., vol. v. p. 421. 



