The Welsh Story of Creation by Kenneth Morris

Kenneth Morris first met Ella Young (1867-1956) in Dublin in 1896, and they became reacquainted in California in 1927, after which they kept up a correspondence until Morris's death in 1937.  One of the major topics of their correspondence was Kenneth's love of the classic Chinese poets, and in 1946 Young sorted her Morris letters, and contributed many chunks from them to the Theosophical Society's archives. One extract from the letters was published in The Theosophical Forum of October 1947 under the title of "The Welsh Story of Creation."  It was probably written very soon after 14 February 1928, and it clearly was written in response to a question from Young.  I present the text here as published in 1947:

And now I find you ask about the Welsh account of Creation, which sends me to another sheet. It is as follows: 

The universe periodically manifests and is unmanifested, man­vantaras and pralayas; we call the first “menw-anturiaid.” The beginning was the first occasion of the “Death of God.” He sounded his own name, whereupon all being flashed from latency into existence “more swiftly than the lightning reaches its home.” He, or it, then fell into Annwn and was united with Cythraul (now the devil, then matter) and united itself with the manred, small courses, or circlings, of the atoms; which thereupon began evolving through all imaginable forms in earth, air, fire and water, through elemental, mineral, vegetable and animal kingdoms. 

Thus the Teacher asks, “What are you, and what is your origin?” And the disciple answers, “I am a man in the Circle of Abred, having had my origin in Annwn.” They reckoned that the atom was a solar system consisting of proton-sun and electron-planets; that these planets were themselves worlds with as many inhabitants as this world; that the bodies and matter of these planets and their inhabit­ants were themselves atomic, those atoms being solar systems; their planets inhabited; thus they saw an infinity in the infinitesimal; which they called Annwn, and reckoned that we had evolved up through innumerable imbodiments through it all. But we are not just those manred evolved; because there were the Gwynfydolion in Cylch y Gwynfyd; who had been men made perfect in a previous manvantara; when God sounded his three-lettered name and the universe awoke, they awoke first; and looked out from the peaks of Gwynfyd, and beheld far off the House of God in Ceugant (Infinity); and “Evil on our beards,” they said, “unless for love we take his house by storm!” So they rode forth, the scythes on their chariots gleaming, to take infinity by storm; and, said the Druids, we still are engaged on that adventure. 

For the Gwynfydolion never could cross the Circle of Abred but became involved in it, fell, and united themselves with the souls of the manred that were evolving upwards; and that is why man is half god, half pig-tiger; the higher part of him is the Gwynfydol that came down; the lower half is the manred that ascended.—That, in very brief, is the Welsh explanation of things; and I defy the world to produce a better or a nobler! For here is the cry of the Gwynfydol:

To set my will, were it all in vain,
’Gainst this in-riding tide of pain,
And on the brink of hell to wage
Even losing love-war ’gainst hell’s rage;
Even at the last perchance going down
Drowned in the hell I willed to drown:
This my Nirvâna were—but this!
My goal, demand, reward and bliss!

I have long assumed that Morris's account was based on something in the Barddas of Iolo Morganweg, but are there any other sources for this account?   (I note that E.A. Holmes has written about this account and Barddas in an article in Sunrise for November 1976, which is available online here.)