The following may be a bit redundant, since it duplicates what has already been posted above, but I think it is more free of errors, at least in punctuation and line breaks.

Copied from http://www.dnaco.net/~mobrien/irishptr/iresongs/sibeagsi.html

Sí Bheag is Sí Mhór
Lyrics & Music: Turlough O'Carolan (1670-1738)
Translation: Maureen S. O'Brien

Ó imreas mór tháinig idir na ríona,
Mar fhíoch a d'fhás ón dá chnoc sí,
Mar dúirt an tsí mhór go mb'fhearr í féin,
Faoi dhó, faoi dhó ná'n tsí bheag.

"Ní raibh tú ariamh chomh huasal linn,
I gcéim dar ordaíodh i dtuath nó (i) gcill,
Beir uaim do chaint, níl suairceas ann,
Is coinnigh do chos is do lámh uainn."

"Choiche ní bhfaighfidh sibh bua ar chách,
Ar muir, ar tír ná 'n iomarbhá,
B'fhearr an chídh 'bheith 'déanamh síth
Ná fógairt cogaidh i láthair."

Tráth chruinnigh na sluaite, bhí an bualadh teann.
Ar feadh na machaireacha 'nonn is anall,
's ní raibh aoinne ariamh dar ghluais on mbinn,
Nár chaill a cheann san ár sin.

Is é sin an cath do chráigh ár gcroí,
Na prionsaí sí ar gach taobh
Tuatha Dé Danann ag teacht 'na scaoth'
's nach iontach saolta an t-ár sin.

Is ansin do cailleadh na ríthe sí,
Na mílte díobh ar gach taobh
Ní raibh ach bruíon do scrios an Traoi,
Le méid an áir an lá sin.

Pairlí, pairlí, a chairde gaoil,
Sin chugaibh ár namhaid ó Charn Chlann Aoidh,
Ó Bhinn Eachlainn aníos na sluaite díobh,
Is bímis uile uile páirteach.

Atá siad anois is ariamh dhá rá,
An cogadh is lú go milleann a lán,
Gur fearr an tsíth is measa dlí
Ná bailte is tíortha a bhánú.

'sé an t-éad ar dtðs do dhíbir slua,
's chuir na mílte i gcarcair chrua,
Is fearr an chóir bheith buan go deo,
Ná bráithre a ghríosu in árach.

* * *

Oh, great strife came between the kings,
Feuds grew between their Hills, because
Big Hill folk spoke too well of themselves
While Small Hill burned beneath them.

"You can never share rights to our noble lake.
Go into ranks by tribe or town.
Carry your blemish away from us.
Be happy to keep your hands and feet."

"You cannot always win every fight
On lake, on land, when we contend.
It would be good if you made peace
Instead of ordering wars in here."

Time to gather the hosts, make a striking force.
From throughout the plains, they come marching here.
It will never seem right to die for hills,
Beheaded in that slaughter.

This is why battle pains our hearts:
With Hill princes on every side, and
Tuatha De Danann come in a swarm,
The slaughter is not surprising.

Then it is that the Hill kings lost
The thousands killed on every side.
There was no dwelling not destroyed
In all the killing that day.

"Parley, parley, oh friends and kin!
Our enemy from Cairn Clann Aoidh,
Comes from Eachlainn Peak, up our dead troops!"
Now everyone fights together.

Now no one ever will say twice,
"War isn't caused by too much pride."
Peace is as good as wars were bad.
The towns in both lands are rebuilding.

Envy first, then an eager host,
Then thousands prisoners in the grave --
Better eat words almost forever
Then have angry brothers on their biers.