 His poem "Yr Adgyfodiad" was published in 1849, whilst he was a minister at Tredegar in the Sirhowy Valley.Many other poems, biographies, an autobiography, and a dictionary followed.His dictionary, "Geiriadur Cymreig Cymraeg", published in Caernarfon in 1868 was one of the first dictionaries to be published only in Welsh (rather than English and Welsh).