90 Proceedings of the Royal Physical Society. 



Mr Skipsey states that the genera Anthracojytera and A71- 

 thracomya are much more generally diffused throughout 

 the Measures, but in all cases they are usually found in 

 most perfect condition in the greyish coloured shales, whilst 

 in the black bituminous shales they seldom occur, and then 

 only in single valves.* Anthracomya modiolaris, Mr Grossart 

 tells us, appears to characterise the horizon of the Splint 

 Coal. The same writer has further ascertained that in 

 the celebrated Airdrie Blackband Ironstone, AnthrcLcosia 

 centralis is the most abundant species. The same shell 

 predominates in the Virtuewell Coal, but does extend much 

 beyond that horizon. 



Much writing has been written and many papers published 

 to prove the marine deposition of the Coal Measures in 

 general, but I take it that the special occurrence of marine 

 bands in the measures prove only, and specially, the occa- 

 sional occurrence of truly marine conditions. We must look 

 upon the sediments in which the genera Anthracosia, An- 

 thracoptera, and Anthracomya occur as either of a brackish 

 or a fresh w^ater origin. The probability appears to be, 

 speaking purely from personal experience in a climate where 

 creek and brackish vegetation attains a luxuriant growth, 

 accompanied by a rapid humus-accumulation of soil, that 

 the brackish water theory deserves more attention than any 

 other which has been advanced. 



The Permian Conchology of Scotland. 



So far as known to the writer the Permian System, as 

 developed in Scotland, has not yielded any, beyond the most 

 indefinite traces of molluscan life. A few years ago Mr P. 

 Dudgeon, F.R.S.E., of Cargen, forwarded to Professor A. 

 Geikie, F.R.S., a few casts from the Permian beds of the 

 County of Dumfries. Beyond ascertaining the relation of 

 these to some Gasteropod liaving a depressed spiral, it was 

 found impossible to regard them as more than mere derived 

 Carboniferous fossils, a fact borne out by the nodular-looking 

 concretions in which the casts were preserved. 



* Skipsoy, loc. ci(., p. 113. 



