County Diiblifi, Past and Prese^it. - -13 



actively pushed forward. The lyongmynd rocks of Shropshire 

 will probably have to be thrust out into the pre-Cambrian ; and 

 Prof. Blake' has wished to honour the rocks of Bray and 

 Howth b}^ assigning to them a similar antiquit}^ 



This great series of rocks, amounting to some z],ooo feet in 

 thickness, has yielded, however, little in the way of fossils. 

 Worm-tubes have been carefully described from Bra}^ and 

 Howth, and have been distinguished by names which exalt 

 them to the rank of fossil genera. Tubes as much as two feet 

 long have thus been observed by Dr. J. R. Kinahan at Bray;^ 

 and the same author has believed that casts of the crown of 

 tentacles which occur around the head of many worms, such 

 as the modern Serpula, are traceable in certain diagonal mark- 

 ings in the fossil, called by him Histioderma? Haughtonia 

 consists of clustered worm-tubes found at the north end of 

 Bray Head.^ 



The fame of the Irish Cambrians has, however, gone out 

 into all the w^orld through the discover}^ by Dr. T. Oldham, ^ in 

 1844, of "small zoophytic markings" in the slates of Bra3^ 

 Prof. Forbes named these Oldhamia four years later,^ and two 

 species were established. Dr. J. R. Kinahan, however, first 

 accurately figured and described them,^ adding a third species 

 discreta, and confirming the general impression that the organism 

 was h^'drozoan, resembling the Sertularians. Considering how 

 minutely wrinkled the rocks of Bray have become by earth- 

 pressures, the question of the organic nature of Oldhamia has 

 been several times raised ; and Prof. Sollas^ has recently sug- 

 gested that comparison may fairly be made between its 

 structure and the delicate folds produced b}^ incipient cleavage 

 in some metamorphic rocks. But the radial series of wTinkles 

 described as O. radiata remains unexplained ; and, as Mr. G. 

 H. Kinahan^ remarks, why should Oldhamia, if inorganic, be 

 confined to the Irish Cambrians ? Clearly we have here a 

 subject which may be in the end conclusively elucidated by 

 local research. Oldhainia aiitiqua has been found at Puck's 

 Rocks, Howth ; and both the well know^n species are widely 

 vSpread in Co. Wicklow. The search for Oldhamia may also be 

 fruitful in revealing traces of other organisms ; if not Olenellus 

 and its associates, y^X. perhaps something even more ancient and 

 more interesting. Mr. Jolj^'s paper/" pointing out a curious 



^ "The Monian System of Rocks," Qiiar. Journ. GcoL Soc. London, xliv. 

 (1888), p. 534. 

 "■ G. S. D. vii. (1856), p. 185. 

 ^ lb. viii., p. 70. 



* Misprinted " Howtli " in the original paper, G. S. D. viii., p. 116. 

 ^ G. S. D. iii., p. 60. 

 ^ lb. iv., p. 20. 



7 lb. viii. (1858), p. 69, and Trans. Roy. Irish Acad, xxiii., p. 547. 



8 lb. vii., pp. 171 and 174. 



9 " On Oldhamia," G. S. I. vii., p. 166. 

 ^0 G. S. I. vii., p. 176. 



