Vol. 68. J PALJEONTOLOGT OF THE WAKWICZSHIEE COALFIELD. 593 



the chief seams of coal; the strata have a prevalent gre}^ tint, and 

 possess an abundant flora and fauna. 



The upper subdivision, about 2000 feet thick, contains only a 

 few, thin, impersistent seams of coal ; its constituent strata have, 

 on the whole, a prevalent red tint. This distinction in litho- 

 logical character is accompanied by a remarkable absence of animal 

 life, and by the occurrence of a limited but characteristic flora, very 

 different from that of the loAver subdivision. 



These two subdivisions, the Productive Measures and the Barren 

 Measures, are separately dealt with in the following description. 



The Productive Coal Measures. — Prom base to summit the 

 strata are made up of repeated alternations of sandstone, underclay, 

 and shale, with beds of ironstone and coal-seams. The rocks fall 

 naturally into a lower argillaceous series, which contains the 

 workable seams of coal, and an upper arenaceous series,'^ which 

 contains only a few thin seams. In lithological character these 

 rocks show a general similarity to the Productive Measures of the 

 other coalfields of the Midlands, but a few minor differences have 

 been observed. The coals belong exclusively to the bituminous 

 variety, steam-coals and cannel-coals being practically unrepre- 

 sented. Locally some of these seams, more particularly the Thick 

 Coal, contain numerous macrospores, which are found in a flattened 

 state between the planes of bedding of the dull hard layers of the 

 coal. Macrospores have also been obtained from the shales overlying 

 the coal. In the Stockingford clay-pit fossil trees (Sigillaria) sue 

 not uncommon. They are found both erect and recumbent, being 

 usually preserved as casts in ironstone, but sometimes as casts in 

 shale. These casts attain a diameter of several feet, and are often 

 accompanied by a thin layer of coal representing the bark. Some- 

 times such erect trees, often many feet long, may be observed to 

 extend almost vertically across the beds of shale separating two 

 seams of coal. In such cases it may be inferred that the time taken 

 for the deposition of the strata separating the coal-seams must 

 have been comparatively short. 



Nodules and bands of clay-ironstone occur at several horizons, 

 interstratified with the shales and sometimes even with the coals. 

 The smaller symmetrical nodules are sometimes fossiliferous ; while 

 the large, irregular, septarian ironstones or ' big balls,' which fre- 

 quently attain a diameter of 6 feet, are almost invariably barren. 

 A peculiar form of oolitic ironstone or ' sphserosiderite,' composed 

 of small si3herules of siderite, frequently occurs in the fireclays and 

 sometimes in the coal. 



Underclay s and sandstones are of common occurrence : the former 

 tending to predominate in the south of the coalfield, and the latter 

 in the north. 



There is abundant proof, in the form of local breccias, * wash- 

 outs,' and local unconformities, that the deposition of the Coal 



^ Including the Four-Feet Sandstone (see vertical section, PI. LXI). 

 Q. J. G. S. No. 272. 2 tj 



