The song is Eanach Dhúin (although in the recently-published Leabhar Mór na nAmhrán [Cló Iar-Chonnacht] it is called Eanach Cuain) after the place name where the disaster took place. As a child I heard more verses of it than have appeared on this thread, including this one:
Ansiúd Dé hAoine,
'sea chluinfeá an caoineadh
Ag teacht ó ghach taobh díot
is an greadadh bos;
is a lán thar oíche,
trom tuirseach cloíte,
Gan ceo le déanamh acu
ach ag síneadh coirp.
A Dhia is a Chríosta,
d'fhulaing íobairt
a cheannaigh go fíreannach
an bocht is an nocht,
Go Párthas naofa,
go dtugair saor leat
gach créatúr díobh
dar thuit faoin lot.

I remembered only the the first four lines of that verse but the rest I got from the above-mentioned book, which also give three other vereses.