Antiquary
Not the least of Clark's fame attaches to his great work Cartae et Alia Munimenta Quae ad Dominium de Glamorgancia Pertinent (Charters and Other Muniments which Pertain to the Lordship of Glamorgan), published in 6 vols. at Cardiff in 1910. On this monumental work is built most of the reconstructed mediaeval history of Glamorgan and much of the later history up to the 16th.c. It consists of transcripts of some 1,660 ancient charters, numbered in Roman numerals, in their original language and spelling, which Clark had searched out from various sources including Margam Abbey and Ewenny Priory. It is an invaluable work to historians and genealogists alike, and is a tribute to the energy of a man who found the time to engage on such a project in addition to his business interests. His familiarity with the names of old Glamorgan led him to produce another great work, on Welsh genealogy, "Limbus Patrum Morganiae et Glamorganiae (trans: The Border/Fringe/Hem of the Fathers, perhaps in the sense of "remnants of the ancient chieftains"): Being the Genealogies of the Older Families of the Lordships of Morgan and Glamorgan". Published in 1886.
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