Note 121 — Chapter XI · THE CAMBRIAN VOLCANOES OF NORTH WALES, THE MALVERN HILLS AND WARWICKSHIRE
Reading edition
Mem. Geol. Surv. vol. iii. 2nd edit. p. 252.
[122] A group of cherts and mudstones not more than 60 or 70 feet thick appear in that region to be stratigraphically equivalent to the great depth of sedimentary material which elsewhere constitutes the Upper Arenig and Lower and Middle Llandeilo formations. See Annual Report of the Geological Survey for 1895, p. 27 of reprint.