512 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 6, 



immediately to the south-west of them the metamorphio strata 

 whence these conglomerates have been derived preseot themselves, 

 with the normal east and west strike. 



The fossils which were collected by myself and by Mr. G. H. 

 Kinnahan, of the Irish Geological Survey, who accompanied me during 

 part of the time I spent among the fossiliferous Silurian strata of co. 

 Galway,are the following: — Favosites Gothlandica, Alveolites Lahechii, 

 Halysites catemdatus, Petraia hina, P. ziczac, M'Coy, Pleurodictyum 

 jprohlematicum* , Pliacojps suhlcevis, M'Coy, Encnnurus punctatus, 

 Fenestella prisca, Ptilodictya lanceolata, Atrypa hemisjoJicerica, Orthis 

 reversa, Pentamerus ohlongus, Spirifer plicatellus var. Indians, Trochus 

 midtitorquatus, Holopella ohsoleta, Bellerophon. 



The fossiliferous Silurian rocks of Galway, although on the whole 

 dipping from the metamorphic rocks on the north side of which they 

 repose, have many local irregularities. They are succeeded towards 

 the eastern end of Killery Harbour by grey- and purplish- coloured 

 pebbly grits, in which no fossils have yet been found. 



These grits are false-bedded ; but their strike and dip seem to con- 

 form to those of the fossiliferous Silurian beds on which they repose. 

 They appear to form a synclinal trough near the head of Killery Har- 

 bour, as on the south side they have a northerly dip, and on the north 

 of this harbour they incline towards the south. These grits form a 

 very bold and rugged mountainous district, in which is Mweekea 

 (2692 ft.), one of the highest mountains in this portion of Ireland, 

 at the northern entrance into KiUery Harbour. 



Eastwards from Killery Harbour these rocks appear in the form 

 of rugged precipices, forming the northern side of the mountains 

 which occur on the south side of the Errive Eiver. 



The grey and purple grits which overlie the fossiliferous Silurian 

 strata have a great lithological affinity to the so-called Old Red 

 Sandstones which occur to the south of the greenstones and fossili- 

 ferous Silurian (Caradoc) deposits of Pomeroy, co. Tyrone. 



The fossils of the unaltered rocks of the west of Galway are such 

 as to indicate an horizon more nearly parallel with that of the Upper 

 Llandovery rocks than any other in the Silurian system. Of 

 these fossils, Atrypa hemisphcerica is by far the most abundant, and is 

 one of the most characteristic of the Upper Llandovery Brachiopods, 

 besides which we have a smooth Pentamerus. The Trilobite which 

 occurs most frequently is Encrinurus punctatiis. With these fossils 

 other Upper Llandovery forms are found ; and, although the corals 

 indicate a somewhat higher position among the Silurian rocks, the 

 whole fades of organic remains justifies the inference that the 

 fossiliferous Silurian strata of Galway belong to the middle portion 

 of the Silurian system. 



* This, I have no doubt, is not strictly a fossil, but the cast of the upper por- 

 tion of the cup of a tabulate coral. On taking a cast of the 'Pleurodictyum above 

 mentioned, and comparing it with the upper surface of Favosites Gothlandica, 

 I could distinguish no difference in form. The tube-like body which so fre- 

 quently accompanies Pleurodictyum fvohlematicum appears to be a cast of the 

 burrow of a parasite like the Siimnculus heterocyathus, which bored through 

 corals belonging to the genus Hcterocyathus (vide Nat. Hist. Keview, n. s., vol. 

 ii. p. 80). 



