Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/32

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strata I am about to describe occur in the north-west corner of Shropshire and in the adjacent south-east corner of Denbighshire. They are cut through by the rivers Ceiriog and Dee; and a good section of a portion of them may be seen along the banks of the Dee, from the mouth of the Ceiriog downwards towards Erbistock.

I directed attention to these beds in the year 1873. Since that time I have been engaged constantly in colliery operations in the district and strata then referred to; and I propose in this communication to narrate the results of my observations during the interval, and also to inquire into the relative position of these strata with others which are usually described as Permian.

The order of the beds and their relation to the underlying Coal-measures will be understood by a reference to the horizontal section which accompanies this paper (Pl. I. B). This section extends from the Brynkinallt Colliery, near Chirk, on the west, past the new sinkings of the Ifton-Rhyn Collieries on the east. The line of the section was carefully surveyed by Mr. E. B. Henderson, F.G.S.; and the geological details are supplied by the section of the Brynkinallt Colliery on the west, the Hafod-y-bwch pit-section on the north, the recent sinkings and borings at Ifton on the east, taken together with the outcrops of the strata which are visible along the line of the section.

Section no. 11, of the Diagram of Sections (Pl. I.), gives in a condensed form the details of the strata to be described from the Spirorbis-limestone upwards.

Prior to the year 1873 this limestone had not been recognized in the North-Shropshire and North-Wales coal-field. Early in that year I was taken to see some supposed ironstone beds in the Pentre-Isaf ravine, near Wynnstay. I was struck with the calcareous nature of these supposed ironstones; and upon a close examination I observed the little spiral shell, Spirorbis carbonarius, together with another minute shell which Mr. Etheridge, to whom I submitted a specimen of the limestone, regards as Cythere scotoburdigalensis. Both Mr. Etheridge and Mr. Daniel Jones, F.G.S., who has paid much attention to the Spirorbis-limestone in South Shropshire and the Forest of Wyre, confirmed me in the conclusion I came to, that the supposed ironstone beds were none other than the Spirorbis-limestone itself. I may on a future occasion describe these limestones and their associated strata more minutely; at present I would simply add that in February of this year the same limestones were passed through in the No. 3 pit, at Ifton-Bhyn Collieries on