Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/35

Rh The clays interstratified with these coals are full of the rootlets of Stigmaria ficoides; and the overlying shale, which is four or five yards thick, is charged with Sigillariæ, Calamites, and Lepidodendra, of several species, Pecopteris (Bucklandi ?), Neuropteris cordata, Asterophyllites, Araucarites, Dadoxylon, Sternbergia, and other plant-remains, the grouping being similar to that of the lower seam just described.

Above this shale we reach a rock which is known in the district as the Coedyrallt rock, a good section of which may be obtained in the Coedyrallt wood on the right bank of the Dee, a little below the junction of the Ceiriog with that river. It is also worked in quarries along its outcrop on the right bank of the valley of the Morlas. North of the Dee it is quarried in Wynnstay Park, as well as near a farm-house one mile to the N.E. of Ruabon.

It consists of buff, yellow, and greenish grey sandstones, in which obscure traces of organic remains are found. These sandstones enclose large irregular masses of limestone, which are not drifted fragments, but which form integral parts of the rock.

The limestone is usually grey in colour and of a coarse crystalline texture. Some idea of the quantity of calcareous matter contained in this rock may be formed from the fact that below Escob Mill, on the right bank of the brook Morlas, a deposit of calcareous tufa of considerable extent and thickness has been formed by water percolating through it.

The rock also contains in its upper portion a bed six feet thick, of calcareous nodules and concretions set in a clayey matrix. Above the Coedyrallt rock, which varies in thickness from 40 to 80 feet, is a bed of red marl; shales follow until, at a height 210 feet above the Morlas-main coal, we reach a double coal-seam with a parting of fine fire-clay, as follows:—

This coal has been worked a little in the "New Flannog Pit." It is succeeded by 45 feet of blue and dark grey shales, which are capped by a rock which, in the New Flannog pit, was about 6 feet thick.

This rock cannot, I think, be far from the base of the dark red sandstones, group 4 of Section 11; but the exact distance is not at present ascertained.

Good sections of these upper sandstones may be seen along the left bank of the Dee from near the new bridge recently erected on the Penyllan estate to Erbistock ferry. Fragmentary sections are also seen in the brooks about Pant Mill. Near their base these beds are of a marly nature; but they become massive sandstones as we ascend. Towards their middle portion there are occasional irregular beds of small pebbles. There is much false-bedding among the sandstones, which also vary in colour from brown to grey; they also contain white gypsiferous bands.