THE tangled narratives of the relationship between Ireland and Britain -- and among the people of Ireland, north and south -- are littered with broken promises, betrayals and easy solutions.
The shattered hopes are so embedded in the glaciers of unforgiving history that one reads with trepidation Wednesday's declaration of a "framework of peace" by the governments in London and Dublin.
But this is the very brightest possibility to have emerged in the quarter-century's violence that has claimed 3,000 lives -- Protestants and Roman Catholics, gunmen, soldiers, civilians, children.
The two governments have produced a formula that expresses the root requirement for success: that all the people of Ireland, and only the people of Ireland, are to determine the future of their island.
The Irish can, the agreement says, "exercise their right of self-determination."
It is as if the seismic shocks that traveled across Europe and the Middle East recently have at last crossed the English Channel and Irish Sea.
The task that lies before negotiators, official and unofficial, is Herculean: producing language that can persuade the Irish Republican Army to give up its bloody campaign while persuading Protestant Unionists that their community's British identity will be safeguarded.
In principle, the task is impossible, the two aims being mutually exclusive. The hope is that the glaciers have not only been moving but also melting a bit, allowing peace a narrow passageway.
Recent months have given cause for hope: the talks between Gerry Adams of Sinn Fein, the IRA's political wing, and John Hume, who speaks for the vast nonviolent Catholic community in the North; Prime Minister John Major's decision to make an Irish solution the British government's first order of business and the growing wish among the English to have done with the whole thing.
There has also been a clear movement in the republic away from the old tribal totems, as symbolized by increasingly liberal attitudes toward divorce and contraception and by the election of a progressively-minded woman, Mary Robinson, as president.
And the south has shown a growing desire to get rid of the articles in its constitution that assert de jure sovereignty over the entire island.
Even among northern Unionists there seems a certain weary, resigned relaxation of their traditional vigilance.
The Rev. Ian Paisley, the leading Protestant hard-liner, increasingly seems an ice-encrusted fragment of the glacier, adrift and bobbing, clutching in his frozen hands his Cromwellian battle standards.
Figures more sinister than Paisley lurk behind the curtains on either side: IRA gunmen who may prove irreconcilable and less politically minded than Gerry Adams and Protestant gunmen who believe what Paisley taught them (and for which he will eventually answer to that old friend of his, Almighty God).
For the present, however, the declaration from Downing Street is a more welcome Christmas gift than bombs in Harrods.
Doubtless, it issues from a variety of motives on all sides -- noble, ignoble and just plain political.
But that is how history melts its glaciers.
Thomas Flanagan is author of "The Tenants of Time" and the forthcoming "The End of the Hunt," about the 1919-1921 war between England and Ireland.