Note 177 — Chapter XIII · THE ERUPTIONS OF LLANDEILO AND BALA AGE
Reading edition
Silurian System, 1839, p. 330. The occurrence of "trappean ash" with fossils in the Builth district was noticed by De la Beche, Mem. Geol. Surv. vol. i. (1846), p. 31.
[178] See Sheet 56 of the one-inch map and Sheets 5 and 6 of the Horizontal Sections.
[179] Catalogue of Rock Specimens, 3rd edit. 1862, p. 36 et seq.