552 PEOF. E. J. GAEWOOD OX THE LOWEE CAEBOXIFEEOTJS [DeC. I9I2,. 



So far as stratigraphical evidence is concerned, the Sinrifer- 

 pinskeyensis Beds may be of an}^ age between Upper Devonian and 

 the Zaplirentis Zone of the Bristol succession inclusive. The- 

 evidence from fossils, especially fish-remains, taken together witli 

 the general probabilities, though perhaps not absolutely conclusive,^ 

 appears to point to the deposits being of Carboniferous rather than 

 Devonian age, although the exact correlation of these beds with 

 the corresponding beds in the South- Western Province at present 

 remains unsettled. 



With the exception, then, of the depression in which the Pinskey 

 Beds occur, the North-Western Province was not submerged until 

 a period when the upper portion of the Zaphrentis Zone was being 

 deposited in the South- Western Province, while the submergence 

 of some parts of the area did not take place until a still later 

 period, when the C^ beds of Bristol were being laid down. 

 Judging by the character of the deposits first laid down, the Lower 

 Palaeozoic floor on which the Carboniferous rocks now rest must 

 have been of the nature of a peneplain rather than a plain of 

 marine denudation. 



The earliest deposits, consisting as they do of dolomites and 

 porcellanous limestones almost free from admixture of mechanical 

 sediments, would appear to have been laid down in a land-locked 

 lagoon-like area, from which wave- and current-action was entirely 

 excluded. This supposition is confirmed by the character of the 

 organisms which are entombed in these deposits. The presence 

 of calcareous algae, in such abundance as occasionally to make up 

 the bulk of the rock, sufiiciently testifies to the lagoon-like con- 

 ditions which prevailed during their growth ; while the wealth of 

 brachiopods, such as AiJiyris glahristria and Camarotoechia j^roava,. 

 some of which occur unbroken, with their valves united and their 

 brachial supports intact, j)oints to the same conclusion. In the 

 case of Athyris, even the delicate external fringes are not infre- 

 quently found still attached to the surface of the shell. 



The dolomitization of the limestones, if we regard it as practically 

 contemporaneous with the deposits, would seem most naturally to 

 have taken jDlace under conditions similar to those which now 

 exist in the neighbourhood of barrier-reefs and atolls, as shown 

 by the recent investigation on the composition of coral-reefs.^ An 

 interesting point in connexion with the distribution of these earlier 

 deposits is their relation to the underlying Lower Palaeozoic rocks- 

 over the I^orth- Western Area. According to one view, the Lower 

 Carboniferous sediments were deposited against an island of Lower 

 Palaeozoic rocks which rose above the sea near the centre of the 

 area, so that, as this island sank, it was covered by successively 

 higher deposits of Carboniferous age, and its centre may even have 

 remained above the surface throughout the duration of the Lower 

 Carboniferous sea. 



1 Eeport of the Coral-Eeef Committee of the Eoyal Society : 'The Atoll of 

 Funafuti' 1904. 



