It appears that the Church of Jesus Christ of Latter-day Saints (LDS or Mormon) in Wales first began using a standard ledger book form for membership records in 1849-50. I have seen them from the Branches in Merthyr Tydful, Tredegar (Bedwellty Parish), and Risca, Wales. The format covered two, long pages lengthwise. When the register book was open, the two pages formed continuous lines across the two pages. Fortunately, a few of them have translation in English. An example follows with some of the columns translated into English. I will attempt to translate and explain the rest. The first page:
"Cofres-LLyfr" means "Register-Book" and that's an interesting, gothic, double "L" in "LLyfr."
"o Aelodau" is "of members."
"Eglwys Jesu Crist Saint y Dyddiau Liweddaf" should be obvious as "The Church of Jesus Christ of Latter-day Saints." And remarkably for Welsh, in shorter form than most languages with Roman script. 'Saint" is in a singular form as there are nouns like "plant" for "child" that are often used to mean a plural group ("children") but remain grammatically singular in form.
"ym gynnalledig" is along the idea of "maintained" or "established."
The columns and blocks below are contemporaneously translated up to "Difuddywid" shockingly translated directly as "damaged" but has the meaning of "deprived" or our complicated word "excommunicated." I have seem membership lists both in Wales and in the US where names are crossed-out, literally "blotted-out."
"Pa bryd" they have up there already as "when." And "Am ba beth" is something like "Whatever thing it was" that I'm going to translate as "Cause."
The register continues across the next page with these headings:
On the top of the page we have, "Yn Nghangen ____," which is "In the ____ Branch" with its beautiful nasal mutation.
And "Yn Nghynnadledd" with another nasal mutation, "In the ____ Conference" which was used in LDS Missions before Districts.
The first column is, "Derbyniwyd Trwy Lythyr" "Accepted or Received by Letter" which is how a member could have his membership transferred to another location where the Church was established. The sub-columns are, "Pa byd" or "when," then "O ba Gangen" "From what Branch," and "Yn Ddechrenal" is something about "ending" so it must be calling for the date the membership in the old Branch ended.
"Trosglwyddwyd" is "Transferred" which means they left for another Branch.
The sub-columns are "Pa byd" or "when," and "I ba Gangen" or "To what Branch."
"Ordeinywyd yn Ddiacon" is a more obvious "Ordained as a Deacon" with "when" and "Gan hwy," "By whom."
The other Aaronic Priesthood offices follow; "Athraw" is "Teacher," and "Offeiriad" is "Priest."
Then, "Henuriad" is "Elder" with the direct translation from the stem "hen" for "old." The term would have been familiar to the Welsh with the multiple Non-Conformist Protestant Denominations prevalent.
"Bu farw" is "Died."
"Ymfudodd" is the sad and wonderful "Emigrated."
"No Diadau" is something I'm not quite getting, but it might be to "what nation." Maybe they put the date of emigration in one box and to where in the second. Although I only see the dates in my own ancestors' boxes and pretty much the whole purpose of emigration for the Saints was to go to the New Zion in America.
Any help from better Welsh speakers than I would be much appreciated to refine this analysis.