[Byron left this Preface in an unfinished state, and it was not published until 1901. I have followed the text in the Riverside Press Edition of Leslie A. Marchand.]
In a note or a preface (I forget which) by Mr. W. Wordsworth to a poem , the Subject of which, as far as it is intelligible, is the remorse of an unnatural mother for the destruction of a natural child, the courteous Reader is desired to extend his usual courtesy so far as to suppose that the narrative is narrated by "the Captain of a Merchantman or small trading vessel, lately retired upon a small monthly annuity to some inland town, etc., etc." I quote from memory, but conceive the above to be the sense, as far as there is Sense, of the note or preface to the aforesaid poem — as far as it was a poem.
The poem, or production, to which I allude, is that which begins with — "There is a thorn, it is so old" — and then the Poet informs all who are willing to be informed, that its age was such as to leave great difficulty in the conception of its ever having been young at all — which is as much to say, either that it was Coeval with the Creator of all things, or that it had been born Old, and was thus appropriately by antithesis devoted to the Commemoration of a child that died young. The pond near it is described, according to mensuration,
"I measured it from side to side:
'Tis three feet long and two feet wide." 
Let me be excused from being particular in the detail of such things, as this is the Sort of writing which has superseded and degraded Pope in the eyes of the discerning British Public; and this Man is the kind of Poet, who, in the same manner that Joanna Southcote found many thousand people to take her Dropsy for God Almight re-impregnated, has found some hundreds of persons to misbelieve in his insanities, and hold him out as a kind of poetical Emanuel Swedenborg — a Richard Brothers , a parson Tozer — half Enthusiast and half Imposter.
This rustic Gongora  and vulgar Marini  of his Country's taste has long abondoned a mind capable of better things to the production of such trash as may support the reveries which he would reduce into a System of prosaic raving, that is to supersede all that hitherto by the best and wisest of our fathers has been deemed poetry, and for his success — and what mountebank will not find proselytes? (from Count Cagliostro to Madame Krudener) — he may partly thank his absurdity, and partly his having lent his more downright and unmeasured prose to the aid of a political party, with acknowledges its real weakness, though fenced with the whole armour of artificial Power, and defended by all the ingenuity of purchased Talent, in liberally rewarding with praise and pay even the meanest of its advocates. Amongst these last in self-degradation, this Thraso of poetry has long been a Gnatho of Politics , and may be met in print at some booksellers and several trunk-makers, and in person at dinner at Lord Lonsdale's.
The Reader, who has acquiesced in Mr. W. Wordsworth's supposition that his "Misery oh Misery" is related by the "Captain of a small, etc.," is requested to suppose, by a like exertion of Imagination, that the following epic Narrative is told by a Spanish Gentleman in a village in the Sierra Morena in the road between Monasterio and Seville, sitting at the door of a Posada, and with the Curate of the hamlet on his right hand, a Segar in his mouth, a Jug of Malaga, or perhaps "right Sherris," before him on a small table containing the relics of an Olla Podrida: the time, Sunset: at some distance, a groupe of black-eyed peasantry are dancing to the sound of flute the of a Portuguese servant belonging to to two foreign travellers, who have, and hour ago, dismounted from their horses to spend the night on their way to the Capital of Andalusia. Of these, one is attending to the story; and the other, having sauntered further, is watching the beautiful movements of a tall peasant Girl, whose whole Soul is in her eyes and her heart in the dance, of which she is the Magnet to ten thousand feelings that vibrate with her own. Not far off a knot of French prisoners are contending with each other, at the grated lattice of their temporary confinement, for a view of the twilight festival. The two foremost are a couple of hussars, one of whom has a bandage on his forehead yet stained with the blood of a Sabre cut, received in the recent skirmish which deprived him of his lawless freedom: his eyes sparkle in unison, and his fingers beat time against the bars of his prison to the sound of a Fandango which is fleeting before him.
Having supposed as much of this as the utter impossibility of such a supposition will admit, the reader is requested to extend his supposed power of supposing so far as to conceive, that the dedication to Mr. Southey and several stanzas of the poem itself are interpolated by the English Editor. He may also imagine various causes for the tenor of the dedication. It may be presumed to be the production of a present Whig, who, after being bred a transubstantial Tory, apostasized in an unguarded moment, and, incensed at having got nothing by the exchange, has, in utter envy of the better success of the author of Walter Tyler, vented his renegado rancour on that immaculate person, for whose future immortality and present purity we have the best authority in his own repeated assurances. Or it may be supposed the work of a rival poet, obscured, if not by the present ready popularity of Mr. Southey, yet by the Post obits he has granted upon Posterity and usorious self-applause, in which he has anticipated, with some profusion perhaps, the opinion of future ages, who are always more enlightened that comtemporaries — more especially in the eyes of those, whose figure in their own times has been disproportioned to their deserts. What Mr. Southey's deserts are, no one knows better than Mr. Southey: all his latter writings have displayed the writhing of a weakly human creature, conscious of owing its worldly elevation to its own debasement (like a man who has made a fortune by the Slave-trade, or the retired keeper of a Gaming house or Brothel), and struggling convulsively to deceive others without the power of lying to himself.
But to resume: the dedication may be further supposed to be produced by some one who may have a cause of aversion from the said Southey, for some personal reason — perhaps a gross calumny invented or circulated by this Pantisocratic apostle of Apostasy, who is sometimes as unguarded in his assertions as atrocious in his conjectures, and feels the cravings of his wretched Vanity disappointed in its nobler hopes, and reduced to prey upon such Snatches of fame as his contribution ot the Quarterly Review, and to consequent praise with which a powerful Journal repays its assistants, can afford him, by the abuse of whosoever may be more consistent or more successful than himself,and the provincial gang of scribblers gathered round him.