258 MR. W. GIBSON ON THE CHARACTEE OF [May I9OI, 



An example of this gradual palseontological change is illustrated by 

 the genus Anihracomya. Throughout the lower part of the pro- 

 ductive measures large species of this genus are abundant. Above 

 the Knowles Coal (p. 253) the large robust forms are replaced by 

 the much smaller and thin-valved species Anihracomya Phillipsit, 

 This fossil occurs sparingly in the Knowles ironstone.^ It is found 

 in some black shales below the Little Row Coal (see the measured 

 section, below), and becomes very abundant in all the Black-Band 

 ironstones of the Black-Band Series. 



While the palseontological evidence thus records slowly-changing 

 conditions, the transition is no less clearly demonstrated by strati- 

 graphical data. Thus the Bassey Mine Coal always overlies the 

 Little Row Coal and the Peacock Coal (a seam easily identified 

 throughout the district), and these in turn rest upon strata con- 

 taining recognized coal-seams. The strata above and below the 

 Bassey Mine are identical in character, as shown in the following 

 section measured in the marl-pit near Cobridge Railway-station : — 



Feet. Inches. 



/'White clay 5 



p I Limestone. — Spirorhis, Carhonia 1 2 



% • I Nodular grey marls 15 



"" Grey marl 5 



Dark sbale 6 



Grey marl 22 



Bassey Mine Ironstone. — Anthracomya Pklllipsii... 6 



Bassey Mine Coal , 2 



/^Greymarls 13 



Little Eow Coal 1 6 



Black shale 1 6 



Grey marl 9 





r ^ 

 O « 





PS H 



^ •{ Black shale. — Anihracomya Phillipsii 4 



G^rey marl 10 



Grey grit 1 



Grey marl 17 



Peacock Coal. 



Further proof of the close relationship between the barren and 

 the productive series exists in the simultaneous gradual increase or 

 decrease in thickness as the two groups are traced from south to north 

 on the one hand, or from east to west on the other. This is clearly 

 demonstrated on a sheet of vertical sections illustrative of the coal- 

 field which will be published in the course of the present year.""^ 

 It may be stated here that the Black-Band Series at Shelton is 

 150 yards thick ; while at Apedale, 4 miles to the west, the thick- 

 ness is only 90 yards. At Shelton the vertical distance between 

 the Bassey Mine Coal and Eight Feet Banbury (Cockshead Coal) 

 is over 1100 yards ; while at Apedale the distance between those 

 two seams is reduced to 650 yards. 



If there was a break between the upper and the productive series 

 it must have been of short duration, otherwise we are forced to 



1 Wheelton Hind, Monogr. Pal. Soc. vol. xlix (1895) p. 121. 



2 Geol. Surv. Vert. Sect., Sheet 86. 



