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32 



INTRODUCTION. 3 



Name of Formation. Localities. 



STAGE B. Carboniferous Limestone. — Massive limestone, Wales, North and South; Derby- 

 passing northwards into several beds, with intervening shire, Yorkshire, Cumberland ; 

 shales and grits. in Scotland, the Lower or 



Fossils. — Fish, Crustacea, Molluscs, Crinoids, Corals, Main Limestone. 

 &c, all marine species. 



STAGE A. Lower Limestone Shale and Calciferous Sand- South "Wales, Northumberland, 



stone. — Dark shales in some places ; grits, conglome- and Durham ; in Scotland, 



rates, and red sandstones and shales in the northern " Calciferous Sandstone Se- 



districts. ries." 



Fossils (Marine). — Spiri/era cuspidata, Ehynchonella 

 \ pleurodon, &c. 



Fresh- /- BASIS. Upper Old Bed Sandstone. — Yellow sandstones South "Wales; Northumberland; 

 water < and conglomerates. Scotland (Dura Den) ; Ireland 



Beds. ^-Fossils (fresh- water). — Not well represented in England. (Kiltorcan). 



The marine or fresh-water origin of much of the Coal-measures has always 

 been a disputed point. Palaeontologists have hesitated to affirm the latter on 

 account of the almost universal occurrence throughout the coal-fields of Europe, 

 in some few beds at the base of the Coal-measures, of Unio-like shells with 

 typically marine forms ; but it is questionable whether the presence of the two 

 forms together is not apparent only, — I say apparent because, in collecting fossils 

 from coal-pits, there is always great difficulty in accurately determining, to within 

 a few feet or inches, the exact bed where each one is obtained : very few indeed 

 can be obtained in situ ; the greater part are gathered from the spoil-heaps, where 

 accurate reference to any horizon is next to impossible. A fresh- water bed a few 

 inches thick would pass unnoticed, and its fossils be mixed with those from marine 

 beds above or below it. Many very thin beds containing fossils peculiar to them- 

 selves are known to occur at many geological horizons ; and, as I shall describe 

 hereafter, certain narrow bands, containing a typical marine fauna, do occur in the 

 Upper Carboniferous strata, only to be recognised as of marine origin by their 

 fossil contents. So that I conceive it to be highly probable that thin fresh-water 

 bands exist amongst the marine beds at the base of the Coal-measures, a series 

 universally recognised as one deposited under changing conditions ; and this view 

 is borne out by Prof. Phillips (' Bncyclop. Metrop.,' 1834, p. 590), who describes 

 two bands of Unios in the Gannister Series of Lancashire. 1 



A mixture of marine and fresh-water forms in any bed may be brought about 

 in several ways. It is highly probable that fresh-water forms would be washed 

 down by currents and deposited with marine forms near the bar of the river in 



1 Vide postea, p. 15. 



