KiNAHAN — A New Reading of the Donegal Rocks. 29 



probably no Laurentians in Ireland, but that possibly some of tbe 

 old schistose and gneissose rocks are the equivalents of the " Gap- 

 rocks " between the Cambrians and the Laurentians, those called by 

 Irving and others Agnotozoic, but now called by the United States 

 Survey (after the territory in which they are best developed) 

 Algonkians. Dr. Lawson, however, of the Canadian Survey, has 

 called them Ontarians, which he claims to have a priority. 



The older schistose and gneissose rocks of Ireland are, in 

 general, possibly equivalent to one or other of the groups in these 

 " Gap-rocks" {Algonkians or Ontarians). 



As to the older rocks of the Co. Donegal, in the " Economic 

 Geology of Ireland" it is stated that if the Metallic skeletons 

 found in the black shales of Glendowan are organic remains, 

 those rocks ought to be the equivalents of the Arenigs. Now, how- 

 ever, such a statement must be modified, as we learn that in the 

 black shales of the Canadian Huronians (see ante, page 17) 

 similar Metallic skeletons have been found ; and if so, it suggests 

 that in Donegal, as in Canada, the traces of organic remains may 

 be found in pre-Cambrian rocks. Petrologically the older rocks 

 (which provisionally may be called Kilmacrenans, as they are 

 best developed in that barony), that extend round the later rocks 

 from the Pomeroy district to Pettigo and Ballyshannon, and 

 thence northward and westward into the barony of Kilmacrenan, 

 are members of one system of rocks ; and, if one portion is pre- 

 Cambrian (Algonkian) all ought to be so also. It should, however, 

 be pointed out that, as this area has been very unsatisfactorily 

 examined, it is quite possible that in the Kilmacrenan rocks there 

 is a discordance that would prove a distinct age for different 

 groups. It can, however, be positively asserted that the " Kilma- 

 crenans" are pre-Ordovician, and they may possibly be of pre- 

 Cambrian age. 



The granitic-gneiss, as Gneiss, is evidently nearer than the 

 associated country rocks : that is, all the schistose rocks of the 

 country were in existence, in some form or other, long prior to any 

 portion being metamorphosed into gneiss. The origin of granitic- 

 gneiss is still a vexed question, to which I hope to return in a 

 subsequent Paper, but in this it cannot be entered into. 



The granitic adjuncts of the " Kilmacrenans " belong to at 

 least five distinct systems. First, there are the granites, the 



