Who wrote the poem "Broken Vows" which begins with:  "It is late last
night the dog was speaking of you. The snipe was speaking of you in
her deep marsh".  Irish poet!

Hello.

The verse that you quote was written by Lady Gregory (1852-1932), a
famous Irish poet. It's actually Lady Gregory's translation of an old
Irish poem whose author is unknown.

Here is the complete beginning of the poem:

"O Donall Oge, if you go across the sea,
Bring myself with you and do not forget it;
And you will have a sweetheart for fair days and market days
And the daughter of the King of Greece beside you at night.
It is late last night the dog was speaking of you;
The snipe was speaking of you in her deep marsh.
It is you are the lonely bird through the woods;
And that you may be without a mate until you find me..."

Source:
"... Gregory's much-anthologized version ('Donall Oge: Grief of a
girl's heart') from Kathleen Hoagland, 1000 years of Irish poetry (New
York: Grosset & Dunlap, 1947), 238-240. The original Gaelic version,
with an alternative translation, can be found in Se.n " Tuama, &
Thomas Kinsella, eds, An Duanaire 1600-1900: Poems of the dispossessed
(Dublin: Dolmen, 1981), 288-292."
FOR A POST-FOUCALDIAN LITERARY HISTORY:
A test-case from the Gaelic tradition
Hosted by: litteraturhistorie.au.dk
http://www.litteraturhistorie.au.dk/arbejdspapirer/arbejdspapir_29_00.htm

See this explanation of the poem's origins:

"Yet for all its individual richness, the poem is hard to place or to
contextualize. The most recent anthology of Irish literature classes
it with an amorphous section, without date or authorship, called 'folk
poetry', yet the editors comment that the poem may well be from before
1600, given its great dissemination and popularity all over Ireland
and Gaelic Scotland.

For one, thing, then, what we have here it a disembodied text without
fixed provenance. There is no name given as to its author, and no
dates as to its incipience."
Source:
FOR A POST-FOUCALDIAN LITERARY HISTORY:
A test-case from the Gaelic tradition
Hosted by: litteraturhistorie.au.dk
http://www.litteraturhistorie.au.dk/arbejdspapirer/arbejdspapir_29_00.htm

For more information about Lady Gregory, see this brief biography
hosted by Irishwriters-online.com:
http://www.irishwriters-online.com/ladygregory.html

search strategy: "snipe was speaking of you", "lady gregory"

I hope this helps.

excellent and quick research.

Thank you for the tip.
-juggler