﻿Vol. 66.] THE ORDOVICIAX OF THE GLENSAUL DISTRICT. 271 



VIII. Pal^eontological Notes. By F. R. C. Reed. 



The fossils from this district which have been submitted to me 

 for determination are mostly poor and fragmentary. They occur 

 in two main types of rocks : namely (i) a hard, coarsely crystalline, 

 reddish limestone (97, 155), and (ii) a rotten, gritty, calcareous 

 ash (62). The specimens from the limestones marked 97 & 155 

 apparently belong to the same horizon and come from the same bed 

 at different localities, for the rocks are lithologically identical and 

 the faunas are indistinguishable. This horizon may be unhesi- 

 tatingly correlated with the limestone of the Tourmakeady Beds 

 described on a previous occasion. The more abundant material 

 and newly discovered members of the fauna from these Glensaul 

 localities necessitate a slight revision of my views as to the age of 

 the limestone, and the additional evidence now available points to 

 a somewhat lower horizon than was previously considered to be 

 indicated. In fact, it appears that we must now correlate it with 

 the Scandinavian equivalent of the English Arenig, that is, with the 

 main mass of the OrtJioceras Limestone. My previous reluctance 

 to place the beds so low was due to the insufficiency of the evidence 

 derived from the fossils ; but now there does not appear to exist 

 sufficient ground for refusing to admit that the sediment accumu- 

 lating here in Arenig times was temporarily of a calcareous nature, 

 and that the fauna which nourished during that interval in the 

 West of Ireland was closely similar to that of the Scandinavian 

 seas, where identical physical conditions of sedimentation prevailed. 

 The completely different facies of the fauna, compared with that of 

 the argillaceous beds which were being simultaneously formed in 

 Wales, may be attributed to physical factors, such as the purity of 

 the water and the absence from it of terrigenous material. 



The fauna from the deposit marked 62, which is a rock practically 

 identical with the common type of the Shangort Beds, points to the 

 same general conclusions as to its age and relations. The presence 

 of Nileus armadillo may be regarded as especially important, since 

 this species occurs only in the ecopansus stage (B 2 b) in the Baltic- 

 Provinces, although in Sweden it ranges up into the Cystidean 

 Limestone and in Norway into Etage 4. But the variety depressvs, 

 which most resembles our form, is particularly characteristic of the 

 e.vpansus stage. The presence of a species of CJiasmops in these 

 beds (62) is surprising, and would not seem to warrant us in 

 ascribing the beds to as low a stratigraphical horizon as might 

 otherwise be given to them ; for Schmidt states that, in the Baltic- 

 Provinces, the earliest member of the genus Chasmops occurs in the 

 EcJiinosphazrites Limestone (C,), which he considers to be equivalent 

 to the uppermost OrtJioceras Limestone of Sweden (as developed in 

 Oland and Westrogothia), and to the lower part of the Chasmops 

 Limestone of the same regions. We can explain its occurrence 

 by regarding the Swedish OrtJioceras- Limestone fauna, or a certain 

 portion of it, as having lived on later in the West of Ireland, 

 just as, for instance, the Lower Devonian fauna did in the 



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