STRATA OV SHROPSHIRE AND DENBIGHSHIRE. 11 



the Shropshire side of the river Dee, and three miles S.E. of Pentre 

 Isaf, where they were first seen. Their position is shown on both 

 the horizontal and vertical sections. 



Starting- with the Sjnrorbis -limeatone as our base-line, we have, 

 in ascending order, first a series of red and blue rocks, shales, green 

 and brown sandstone, and grit rocks, with ten thin coal-seams and 

 their underlying clays. The total thickness of this series, from the 

 Spii'orbis-limestone to the topmost coal-seam, is 220 feet. I may 

 here remark that, with some variations, the same strata have been 

 proved in various sinkings and borings in the neighbourhood. 



Above this group of strata we have next about 300 feet of green 

 and greenish-grey rocks with brown and grey sand and gritstones, 

 with pebbly conglomerated and brecciated beds, usually of a 

 greenish colour. These are interstratined with red marls and clays. 

 The green rocks present a great variety of texture ; some are fine- 

 grained sandstones, others rougher grits passing through fine and 

 course breccias into conglomerates. In the Ifton section the frag- 

 ments and pebbles do not exceed three inches in length by one inch 

 and a half in breadth. It is, however, probable that if we could 

 follow these deposits westward to what would be their shore-line, 

 we should find the pebbles and angular fragments increased to 

 boulders and blocks of a larger size. These beds are also exposed 

 along the banks of the rivers Ceiriog and Dee ; and there we find 

 that the breccias and conglomerates are not continuous over a large 

 area, but form oval, wedge-shaped, and irregular masses in the midst 

 of the finer sandstones and marls. 



They thus present the appearance of deposits made in a shallow 

 sea subject to currents, eddies, and storms. The pebbles and frag- 

 ments consist chiefly of Lower or Cambro-Silurian rocks with 

 their imbedded quartz, felspar, greenstone, and porphyry, together 

 with fragments of "Wenlock Shale and Carboniferous Limestone, 

 The whole series indicates a source in the hilly region about Glyn- 

 ceiriog and Llanarmon, which lies from ten to twenty miles west of 

 their present position. Associated with these breccias and con- 

 glomerates are drifted plant-remains. 



It will be seen by a reference to the horizontal section that this 

 series of beds thins out before it reaches the shafts of the Brynkinallt 

 Colliery on the west ; nor is it present, except in an attenuated form, 

 in the Hafod-y-bwch shafts of the Ruabon Colliery, five miles to 

 the north. 



This series of strata is overlain by another of nearly equal thick- 

 ness consisting of red, white, purple and variegated marls. These 

 marls are interstratined in the lower part of the series with red and 

 brown sandstones. In the middle portion there are numerous thin 

 bands of grey calcareous rock. In the upper marls are numerous 

 calcareous clayey concretions charged with crystals of sulphide of 

 iron. 



There are two thin layers of carbonaceous matter in this series — 

 one near the base, in which I have detected traces of Catamites, 

 and one near the middle of the series, which forms a true coal-seam 



