344 Scientific Proceedings, Royal Dublin Society. 



In favour of a Pre- Cambrian age for the Bray Head Series, 

 the following may be noted : — The Welsh Ordovicians pass down- 

 wards conformably into the Cambrians ; but the Leinster equiva- 

 lents of the Ordovicians do not pass thus into the Bray Head Series, 

 as there was evidently a considerable interval between the accumu- 

 lation of these distinct groups of rocks. Furthermore, in the brief 

 description of the Baginbun Promontory, Co. "Wexford (Supple- 

 ment, Irish Arenaceous Rocks, antea, p. 13), it was shown that 

 to the south of Fethard there is an unconformability between the 

 Ordovicians and a group of older fossiliferous rocks ; while the 

 latter are quite unlike in every way those of the Bray Head Series ; 

 it therefore seems probable that they may be a portion of the true 

 Cambrian. Under these circumstances it appears expedient that 

 the rocks of the Bray Head Series should be called by a separate 

 and distinctive name : and for them the term " Oldhamians " 

 may be suggested. 



The Pre-Cambrian age of the Oldhamians seems to be also sug- 

 gested by the geology of Gal way and Mayo, where the equivalents 

 of the Ordovicians pass downwards conformably into a great thick- 

 ness of strata, quite distinct from those of Bray Head ; while in the 

 Mullet, or N. W. Mayo, this group of rooks lies unconformably 

 on certainly one, and possibly two, groups of older strata. 



After careful consideration, it seems to me highly probable 

 that the Oldhamians of S. E. Leinster, and the older rocks of the 

 Mullet, and other places in W. Mayo, are Agnotozoic ; while 

 some of Griffith's older rocks in the Cos. Tyrone, Londonderry, 

 Donegal, and Antrim, might also possibly be similarly classed. 



So far back as 1861, the late Prof. Harkness, in his Paper 

 " On the Pocks of portions of the Highlands of Scotland . . . and 

 their equivalents in the North of Ireland" (Jour. Geol. Soc. Loud., 

 vol. xvii., p. 270), expresses the opinion that the Malin Head 

 gneiss is of the same age as the upper Archgean Pocks of Suther- 

 land, Scotland. 



Carboniferous Sandstone. — It had been anticipated that 

 small outliers of Carboniferous rocks might be found to occur, if 

 properly searched for, on some of the high hills in Donegal and 

 elsewhere. During a late visit of Dr. A. Geikie (Oct. 1888) to 

 S. W. Donegal he discovered, on Slieve League, two considerably- 



