178 STKATIGRAPHICAL GEOLOGY 



Lanarkia, belonging to the family Crelolepidce, which, according 

 to Dr. Traquair, are nearly related to the Pteraspidce, although 

 they have superficial resemblances to the sharks. Other new 

 genera found in these beds are Ateleaspis, BirJcenia, and Lasanius. 

 The Merostomata include species of Stylonurus and Eurypterus, 

 and the Crustacean Ceratiocaris is also present. The underlying 

 Ludlow shales have yielded the earliest British arachnid in the form 

 of a scorpion (Palceophonus), a genus first described from remains in 

 the Silurian of Qottland (Sweden). 



5. Ireland 



Rocks of Silurian age succeed the Ordovician Series in many 

 parts of Ireland ; they may be described as exhibiting two different 

 facies, the one comparable with the Scotch type and the other with 

 the Llandovery-Wenlock type. 



Eastern Facies. Valentian rocks of the Birkhill-Gala type 

 occur in the north-eastern and central counties, and probably they 

 extend under the whole of Central Ireland down to the coasts of 

 Clare and Waterford. Eocks having the same general character as 

 the Birkhill shales and Gala Series of Southern Scotland range 

 through the counties of Down, Armagh, Monaghan, and Cavaii ; it 

 has, in fact, been found that the greater part of the tract which 

 was coloured as " Lower Silurian " on the older geological maps of 

 Ireland consists of Valentian rocks. 19 The older beds (Birkhill 

 shales) occur chiefly along the north-west border of the area, and 

 have yielded the characteristic graptolites, Diplograptus folium, 

 Monograptus gregarius, M. Sedguricki, and Rastrites maximus. 

 South of this zone are rocks of Gala type containing Monograptus 

 priodon, M. turriculatus, and M. riccartonensis, while in County 

 Louth there are rocks comparable to the Riccarton Group with 

 Wenlock fossils. 



Graptolitic Valentian Beds have also been found near Pomeroy 

 in Tyrone, and again far to the south-west in Queen's County, 

 Clare, Tipperary, and Limerick, where large inliers of Silurian 

 rocks are brought up by anticlinal domes from beneath the Old 

 Red Sandstones. 



Western Facies. In the district lying between Lough Mask 

 and Killary Harbour (County Mayo), and again in the Dingle pro- 

 montory of Kerry, there are thick developments of the whole 

 Silurian System, and here the deposits give evidence of the close 

 proximity of land. 



In Mayo, north of Killary Harbour, Llandovery sandstones rest 

 on Arenig Beds, but south of that inlet they overlap the Ordovician 



