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XKXL— OLDHAMIA. By G. H. KINAHAN, M.E.I. A., Etc. 



[Eead, December 15, 1886.] 



The organic origin of Oldhamia has been disputed before now: 

 even at the present time some of the American and Continental 

 geologists seem to dispute it. Such authorities, however, as Forbes 

 J. B. Kinahan, Harkness, and Baily, have carefully examined it,, 

 and I have accepted their opinions ; but at the same time no one 

 is infallible, and there may be a possibility, although, to my mind, 

 an improbability, that they may be wrong. 



As the subject is of interest, I propose to put forward all facts,, 

 as far as I know them, in connection with the occurrence of Old- 

 hamia, some of which appear to me conclusive that it must be of 

 organic origin, while others may suggest that it may be a mineral . 

 structure. 



At one time it seemed to me to be remarkable, that very often 

 the Oldhamia is better developed in shales near an intrude of 

 Quartz-rock than elsewhere. This, however, on going over the 

 evidence, now appears to be more apparent than real. 



In the west portion of Ireland the Cambrians are so much 

 altered that all organic remains are obliterated; it is, therefore, 

 only in eastern Ireland that these can be found. The localities for 

 Cambrian or supposed Cambrian in this portion of Ireland may 

 therefore be given beginning to the north, and in connection with 

 each, stating the peculiarities. 



In the north of the Co. Down, bordering Belfast Lough, are 

 green and purple rocks that appear to be unconformable with the 

 associated Ordovician rocks : these rocks are so like those of Bray 

 Head that DuNoyer classed them as Cambrians. In them Old- 

 hamia has not been found ; nor as far as I am aware are there in 

 connection with them intrudes of Quartz-rock. 



In the Co. Longford, to the east of Grranarcl, there are also 

 more or less similar rocks that seem to be overlaid unconformably 

 by the associated Ordovician rocks. The character of these rocks 

 led Foot and myself to suspect they must be the representatives of 



