ON THE PALEONTOLOGY OF COUNTY DUBLIN, 



BY 



WILLIAM HELLIER BAILY, f.g.s. 

 [Read February 18th, 1878.] 



The fossil-bearing rocks in the vicinity of Dublin, including the 

 adjoining County df Wicklow, belong to the oldest series of 

 formations, being of Cambrian, Silurian and Carboniferous age ; 

 with the exception of a few Pleistocene deposits, containing 

 marine shells in gravels of the Glacial period. 



The Cambrian fossils first claim our attention, as belonging to 

 the oldest fossiliferous formation of the British Islands. From 

 the Bray railway station, a walk along the shore of about a mile 

 brings us to the commencement of the series of rocks forming 

 Bray Head. Certain beds in the hard, sandy shales and slates 

 may be seen to be covered with impressions and markings 

 which were, evidently, organic ; they have been described 

 under the generic name of Oldhamia, after Dr. Oldham, who 

 first made them known. Two species of these remarkable fossils 

 were defined by Professor Forbes : viz., 0. antiqua and 0. radiata. 

 He considered them to belong to the Hydrozoa, and to be. allied 

 to Sertulariau Zoophytes. Others have considered them to 

 be plants, if so, they are most probably Red Alga?, allied to 

 the lime-secreting Corallines. They occur in both green 

 and red or purple slates. On the shore, the best locality 

 for 0. radiata, is the " Periwinkle Rocks," at Bray Point, only to 

 be reached at low water ; the finely laminated green grits at this 

 place being covered with their impressions, and about a mile and 

 a-half further they are plentiful in certain purplish shaly beds, 

 which are interstratified with thicker beds of grit, forming the 

 cliffs rising from the sea at Bray Head, near the " Cable Rock." 

 Good examples of 0. antiqua may be obtained from red beds near 

 the same place, but more inland, a little above the footpath, round 

 the Head, and just within the boundary- wall of Kilruddery 

 Demesne, also at other places close to the same footpath, in cut- 

 tings of the Dublin, Wicklow and Wexford railway, and in 

 various places in the cliffs upon the shore. 



