Efengyliaeth yng Nghymru c.1840-1875 : darlith a draddodwyd yn yr Hen Gapel, Tre'r-ddôl, Medi II, 1982 by A. H. Williams. ISBN 0854850546. Published by Amgueddfa Werin Cymru in 1982. Publication and catalogue information, links to buy online and reader comments.