342 Scientific Proceedings, Royal Dublin Society. 



0. antiqua, and 0. discreta, occurring, but the last are those more 

 generally found. In some places 0. radiata occurred in lenticular 

 pockets of limited extent ; outside of which, although the rocks 

 were exactly ocularly similar, not a trace of Oldhamia could be 

 found. In other places 0. antiqua or discreta might be mixed in the 

 shales, but in general they were confined to thin beds, often not 

 more than the eighth of an inch in thickness ; and in this thin 

 bed, and in no other, could the Oldhamia be found. Some of such 

 thin beds I traced for nearly a furlong. These beds, as also the 

 associated Ordovician rocks, have in them intrudes of Quartz-rock. 



On the west coast of Bannow, close to the fault boundary of 

 the Ordovician, in one four-inch bed of green shales, Oldhamia 

 occurs sparingly. Here there are no intrudes of Quartz-rock. 



In the foregoing I have specially mentioned the intrudes of 

 Quartz-rock, because at one time I suspected there might be some 

 connection between them and Oldhamia ; but the above records 

 seem to disprove such an idea. An Oldhamia bed has a certain 

 look ; and, after hammering bed after bed along the Wexford coast, 

 I came to learn the exact appearance of those in which I would 

 probably find Oldhamia, let the colour be reddish, purplish, or 

 greenish. 



Forbes, J. R. Kinahan, and Baily, from their investigations, 

 come to the conclusion that Oldhamia has an organic origin ; but 

 my knowledge of such organization debars me from giving a posi- 

 tive opinion in their favour. Others say it is not organic ; this 

 also, my knowledge leaves me incapable of refuting. I can, how- 

 ever, legitimately take an intermediate ground. This is not 

 exactly easy to name ; but perhaps it may be called lithological 

 evidence, it referring not so much to the fossils as to the rocks in 

 which they occur ; but before doing so I may refer to the forms 

 of Oldhamia, and the more or less similar mineral forms. 



Oldhamia is said to have a more or less similitude to some of 

 the mineral markings on beds surface, joint planes, and other 

 similar surfaces in rock structure. I have, indeed, seen some 

 dendritic markings somewhat like 0. radiata, but never any that 

 I would mistake for it, as the points of the dendrites have an 

 angular termination quite dissimilar to those of the Oldhamia. 

 As to the impression of 0. antiqua and 0. discreta, I have never 

 seen any surface mineral at all like them. Oldhamia, as it at 



