Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/166

132 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 24, 2. On the Infralias in Yorkshire. By the Rev. J. F. Blake, M.A., F.G.S. With an Appendix on some Bivalve Entomostraca. By Prof. T. RUPERT JONES, F.G.S.

COMPARATIVELY little attention has been paid to the Lias of Yorkshire for some time past ; and consequently it is behind the Lias of other parts as to our knowledge of it. This is especially the case with the lowest beds — the zones of Ammonites angulatus and Am. planorbis —constituting the so-called Infralias, whose presence has as yet been scarcely even recognized. It has long been known that Am. angulatus occurs at Redcar, under the name of A. Redcarensis ; and blocks of stone containing Am. planorbis (syn. erugatus) are thrown up on the coast ; but no section, or list of fossils, has as yet been given of the beds.

In the present paper I hope chiefly to describe some remarkable sections at Cliff, near Market-Weighton, where the Infralias is well exposed, and the fauna it contains is large and interesting. But, while I describe this as the Infralias of Yorkshire, I must express my opinion that it does not form part of the typical Yorkshire basin. On glancing at a geological map of this part of England, it will appear probable that there has existed a ridge in Carboniferous- Limestone times, stretching west from a little south of Flamborough Head, which has separated the coal-basin of South Yorkshire from that of Durham, and made a gap in the overlying Permian rocks ; and though the New Bed Sandstone does not appear to be affected by it, all the overlying Jurassic beds are bent round in a curve on its north side, and to the south appear again as the thin end of a series stretching right across England. The beds to the north form the typical Yorkshire basin, while those at Cliff form part of the thin end of the wider-reaching series. Good sections of all the Infralias beds in the typical Yorkshire basin are still a desideratum, which I am unable to supply ; but when they are discovered, it must be with the Cliff beds that we first compare them. The nearest beds with which to compare these latter, are those at Marton, near Gainsborough, the list of fossils from which, as given by Mr. Ralph Tate in Quart. Journ. Geol. Soc. vol. xxiii. 1867, proves them to contain a somewhat similar fauna, as will be seen in the sequel.

The Infralias beds of Cliff have been briefly described or, rather, noticed by the Rev. W. Norwood, in the ' Geologist,' vol. i. ; but though he recognized their true age, the fossils contained in the beds were so cursorily examined that but little attention has been paid to his paper. Prof. Phillips also mentions them, but only to state their existence.

About three miles from Market-Weighton, on the road to North Cave, at the villages of North and South Cliff, and near the farm of Bielbecks (whose mammalian treasures were described by the Rev. W. V. Harcourt in the ' Phil. Mag.'), are a series of pits opened to extract the Lias clay for marling the adjoining sandy flats.

In the first of these pits (which for want of any local name must be called " Pit No. 1 ") we have the following section : —