150 T, Davidson — On Tertiary Brachiopoda. 



period, we have evidence of at least two centres of volcanic activity 

 in the west of Ireland during the Upper Silurian period, which, for 

 all we know to the contrary, may be but representatives of vastly 

 more extended volcanic regions spreading either beneath the ocean, 

 or beneath formations of more recent age on the land. 



Old Bed Sandstone Period. — The Old Eed Sandstone presents us 

 with several examples of contemporaneous volcanic rocks, both in 

 the northern and southern districts. In the neighbourhood of 

 Boyle, in Co. Eoscommon, there occurs one or more beds of con- 

 solidated ash, interstratified with the red and purple sandstones and 

 conglomerates of that formation.^ In the southern district, one of 

 the most remarkable and well-known cases is that which occurs 

 amongst the Killarney mountains, south of Lough Guitane, and 

 which has been admirably illustrated by the pen and pencil of Mr. 

 Du Noyer, under the direction of Professor Jukes. Here, at Benaun- 

 more, a bold rock reaching an elevation of 1,490 feet, a mass of 

 columnar felstone indicates the position of an old " neck " or volcanic 

 throat, from either side of which stretch, for considerable distances, 

 beds of felspathic ash and agglomerate, with large "balls" of 

 felstone, often hollow in the centre, which were probably bombs, 

 shot out of the vent at various stages of eruption.* These beds of 

 ash re-occur at Lough Garagarry, Lough Managh, and the Devil's 

 Punch Bowl, to the west of Benaunmore, and rise into the summit 

 of Crohane (2,162 feet), and the southern slopes of Killeen moun- 

 tain on the east.^ To the south of this, there is another district, 

 containing contemporaneous trap-rocks, forming the cliffs of Cod's 

 Head and Dursey Island, at the mouth of the Kenmare river.^ 



The shores of Lough Kay and Valentia Harbour present to us 

 another striking instance of a volcanic centre of eruption during 

 this period. Beds of greenstone, felstone, ashes, and agglomerates 

 are here associated with those of Old Eed Sandstone, and pierced by 

 numerous dykes.* 



(To be concluded in our next Number.) 



II. — On the Tektiahy Brachiopoda of Belgium, etc. 

 By Thomas Davidson, F.R.S., F.G.S. 

 (PLATES VII. AND VIII.) 

 N the seventh volume of the Geological Magazine I gave a de- 

 scription, accompanied by illustrations, of all the Brachiopoda 

 then known to me from the Tertiary formations of Italy. I would 

 now offer some notes and figures relative to those that occur in 

 Belgium. 



In order to be able to do justice to the subject, Messrs. Dupont 

 and Nyst kindly forwarded me for examination the best examples 

 preserved in the Museum of Brussels, and I am likewise indebted to 



* Messrs. Jukes and Foot, Journ. Geol. Soc. Ireland, vol. i. part 3, p. 249. 

 ^ Maps of the Geological Survey, Sheets 184, 185, with "Explanations." 



' Ibid. Sheet 198, with " Explanations," pp. 8, 17, etc. 



* Ibid. Sheet 182, with "Explanations," p. 26. 



