[Illustration: +---------------------+ | _Keele Series_ | | | +---------------------+ Newcastle | | +---------------------+ Coal | | | | | _Etruria | | Marls_ | | | Top Red Mine +---------------------+ | | | | Gubbin Ironstone +---------------------+ | | | | | | | | +---------------------+ Knowles Coal | | | | Burnwood Ironstone +---------------------+ | | | | +---------------------+ Mossfield Coal +---------------------+ 5 ft. Coal | | | | | | | | +---------------------+ Hard mine Coal | | | | +---------------------+ Cockshead Coal | | | | +---------------------+ Crabtree Coal +---------------------+ | _Millstone Grit_ | | | +---------------------+ Fig. 8. Coal Measures sequence in North Staffordshire.] The dissimilarities in the fossils of the Coal Measure clays and shales in the Northern and Southern Hemispheres suggest that there is a considerable difference in their formation, but the number of clays and shales which have been examined is too small for any accurate conclusion to be drawn.