348 G. H. Kinahan — Dingle and Glengariff Grits. 



enough to force up the column of lava which fills the tube they 

 have built by piling up ashes, they would find a point of weakness 

 in its sides, and parasitic cones would be formed. When we see 

 such parasitic cones it is not at all unlikely that they may indicate 

 an extinction of visible volcanic energy by means of hydrostatic 

 pressure. 



Nature, however, when working geological changes of this de- 

 scription, works under variable conditions, and if it were possible 

 for' us to determine with certainty the reason why the various 

 volcanos have become extinct, we should find that a complication of 

 causes had been in operation, and in no two cases ought we to 

 expect to find agencies which had been anything more than ap- 

 proximately the same. 



II. — Dingle and Glengariff Grits. 



By G. H. Kinahan, M.R.I.A., 



President Eoyal Geological Society, Ireland. 



(Read before the Royal Geol. Soc. Ireland, April 21st, 1879.) 



FEOM the comments on my discussion of the relations existing 

 between the Dingle beds and the Glengariff grits, with the 

 accompanying diagrammatic section (Geol. of Ireland, chap. iv. p. 

 52), it would appear that it is not as clear as it might be. I therefore 

 propose now to explain myself more fully on this subject. 



But first I would refer to the recently published memoir on " The 

 Old Red Sandstone of Western Europe," by Dr. A. Geikie (Trans. 

 Eoy. Soc. Edinb., vol. xxviii. p. 345), as his statements in reference 

 to the Old lied Sandstone of Scotland are more or less connected 

 with the present question. At page 347 the author states : — 

 1. " My own work in the centre and South of Scotland had proved 

 the Old Eed Sandstone to consist of two great divisions — a Lower 

 passing down conformably into the Upper Silurian Shales, and an 

 Upper graduating upwards into the Lower Carboniferous Sand- 

 stone, with a complete discordance between the two series." At 

 page 353, when contrasting the regular uniformity of the rocks 

 of Silurian age with those of the Old Eed Sandstone, he states 

 respecting the latter : 2. " No such general uniformity of stratifica- 

 tion presents itself. On the contrary, with the accumulation of the 

 deposits in limited basins come local and often peculiar features, 

 whereby even contiguous tracts are distinguished from each other. 

 It is still possible roughly to make out with more or less clearness 

 the limits of these basins, etc." These remarks, as I have shown in 

 a former paper, are very applicable to the Irish rocks ; l as every- 

 where, except in South-west Ireland, the rocks similar to those called 

 by Dr. Geikie " Upper and Lower Old Eed Sandstone " are 

 discordant ; while everywhere the " Upper " graduates into the 

 Carboniferous rocks, and in different localities the Lower passes 

 down conformably into the Silurians. We also find great lithological 



1 Geikie still retains the name Old Eed Sandstone ; but as be bas proyed a complete 

 discordance between tbe Upper and Lower, he has come to the same conclusion as 

 myself, and the names by which the two groups are called does not materially signify. 



