Always curious, found it in "The Cherry Tree" Grigson - he puts the author as Berchan (?-8thC)...

Also found for Meg.Poems following;

The Valley of the Black Pig

The dews drop slowly and dreams gather: unknown spears
Suddenly hurtle before my dream-awakened eyes,
And then the crash of fallen horsemen and the cries
Of unknown perishing armies beat about my ears.
We who still labour by the cromlech on the shore,
The grey cairn on the hill, when day sinks drowned in dew.
Being weary of the world's empires, bow down to you,
Master of the still stars and of the flaming door.

W.B.Yeats.

and (it does have stone in it)

Welcome to the Moon

Welcome, precious stone of the night,
Delight of the skies, precious stone of the night,
Mother of stars, precious stone of the night,
Child reared by the sun, precious stone of the night,
Excellency of stars, precious stone of the night.

From the Gaelic