The organist of our little Welsh church gave me her copy of Ieuan Gwyllt's 1873 or so sol-ffa hymnal, "Cerddor Y Tonic Sol-ffa." There is no front page, so there is no clear evidence of the date of publication, but there is a lot on this book in Google books. It includes what seem like some nice Christmas hymns, "Pa Fwyn Beroriath Glwywaf Draw?';"Pwy Yw'r Baban Egwan;" "Yma Wrth Y Preseb," but Mr. Google strikes out on all three.   
Any information on these hymns would be appreciated. I'm working on our Lessons and Carols program for December and am hoping to add some Welsh carols.
Hoping that more Welsh hymnals will be get on Google books - really amazing what is there now in Welsh. I found a poem that my grandfather wrote in Welsh for the Chicago Welsh Hebron Church in 1906!!
Chris in Portland