Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/752

644 G4I EDWARD HULL ON THE CLASSIFICATION (c) Occasional Marine Beds in Stage E. That the ocean-waters were not far distant from the British and European areas during the formation of the Middle and Upper Coal- measures is proved by the appearance at rare intervals of bands of truly marine shells. Such are those which occur above the " Bay Coal" and the " Gin-mine Coal" in North Staffordshire*, that in the banks of the river Tame at Ashton-under-Lynef, and that of the " Chance Pennystone" of Coalbrook Dale. But it should be observed that the species in these bands are sometimes different from those in the Gannister beds, most of which have descended from the Carboni- ferous Limestone. Thus, out of about 29 species determined by Salter from the Lower Coal-measures (Stage E) of South "Wales J, all but five, viz. Avicidopecten gentilis (Sow.), A. scalaris (Sow.), Myalina triangularis (Sow.), Discites falcatus (Sow.), and Nautilus concavus (Sow.), have been recognized in the Carboniferous Limestone. The species from the same stage in Coalbrook Dale and South Staffordshire are similarly related to those of the Mountain Limestone ; the ex- ceptions to identity are probably owing to insufficient knowledge of the Lower-Carboniferous fauna. On the other hand, if we compare the species from the accidental marine bands which occur in the Middle Measures (Stage E) we find them to be mostly peculiar to that horizon. Thus, out of about ten species from the marine band at Ashton-under-Lyne only one was considered by Salter to be identical with a form from the Gannister beds. Of this remarkable group Mr. Salter has observed : — " A special notice should be given of this marine band, containing as it does a small peculiar fauna, comparable with that of the Lower Coal- measures of Shropshire, but yet wholly distinct. It is true the com- mon marine shell, Avicidopecten papyraceus, occurs in this remark- able band ; but even this is dwarfed, and, except this species, the fossil contents are wholly different from those of the Gannister beds and those of the beds among which they occur"§. These species, nevertheless, may be regarded as the representatives of the fauna living in the adjoining seas during the deposition of the strata of the Middle and Upper Coal-measures, and as such differing to some ex- tent from that of Stage E. It is only thus by accident (as it were) that we obtain a view of the characters of the marine fauna during the long stage of the great coal-growth. (d) Present Mode of Classification Objectionable. With such palseontological evidence before us, it has long seemed to me that the generally received system of classification, by which the whole Carboniferous series is divided into only two great divi- sions, does not express the real relations of the different members to each other. The stages above the Mountain Limestone, including '"■ Discovered by Mr. John Ward, of Longton. t Discovered by Prof. A. II. Green. Rosser vein, a seam above the true Millstone Grit, ' Iron-ores of Great Britain,' part iii. p. 221. § ' Geology of Oldham, &?.' (Mem. Geol. Survey), p. 64.