Papers of Sir Henry Haydn Jones comprising letters dealing with local government affairs, education, elections, local industries, agriculture, and other activities, 1899-1950; correspondence relating to a hymn and tune book compiled by him, 1915-1917; miscellaneous papers, 1836-1880, the earlier papers belonging to his father, J. D. Jones; notebooks containing sermon notes; papers relating to Towyn British School, 1858-1862; Ruthin British School visitors' books, 1849-1864; and papers relating to the Maesypandy and Ynysymaengwyn estates, 1858-1883, the Abergynolwyn Slate and Slab Company, 1924-1939, and the Talyllyn Railway, 1924, 1938-1949.

A typescript dissertation entitled 'A General Survey of the Slate Industry of Caernarvonshire and Merionethshire', by William Morgan Richards, Portmadoc, 1933.

Ledger and journal of Gaewern Slate works, Machynlleth, 1835-1856; accounts and notebooks of the Ratgoed and Cymerau Slate Quarries, Tal-y-llyn, and Llwyngwern Slate Quarry, Llanuwchllyn, 1853-1899; ledgers and notebook of the Cambrian Slate Works, Machynlleth, 1899-1909; minute books of the Abercorris Slate Quarry Company, Rhiwgwreiddyn, Corris, 1893-1909, and the Towyn Company, Tywyn, 1893-1903; and miscellaneous accounts and ledgers, 1827-1909.

Business papers of Jonathan Davies, 1859-1933; papers of Davies Brothers slate merchants, Porthmadog, 1872-1947; personal papers of Jonathan Davies, 1875-1936; and papers relating to friends and family members, [c.1853]-1957. The archive contains a wealth of statistical information about the slate industry in Caernarfonshire, Merioneth and Pembrokeshire and the development of Porthmadog as a slate port.