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 
Fossits.—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.” 
Essentially Marine (except 
Stage A in Scotland) 
Fosstzs (Marine).—Spirifera cuspidata, Rhynchoneila 
pleurodon, &c. 
and conglomerates. Scotland (Dura Den) ; Ireland 
Fossits (fresh-water).—Not well represented in England. (Kiltorean). 
water 
Beds. 
Fresh- oe Upper Old Red Sandstone.—Yellow sandstones South Wales; Northumberland ; 
The marine or fresh-water origin of much of the Coal-measures has always 
been a disputed point. Palewontologists 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 (‘ Encyclop. Metrop.,’ 1834, p. 590), who describes 
two bands of Unios in the Gannister Series of Lancashire." 
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. 
