LONDON - The only major Jane Austen manuscript still in private hands comes up for auction on July 14th, auction house Sotheby's said on Monday.

"The Watsons" by the prolific author of "Sense and Sensibility" is estimated by Sotheby's at 200,000-300,000 pounds ($323,800-$485,700).

"Probably written in 1804, this heavily corrected draft represents the earliest surviving manuscript for a novel by Jane Austen," Sotheby's said in a statement.

"The work, which was not published during her lifetime and remains incomplete, provides a fascinating insight into both her writing practices and her development into one of Britain's greatest authors."

None of the manuscripts of Jane Austen's completed novels survive, with the exception of two draft chapters of "Persuasion" (at the British Library), Austen's juvenile work "Lady Susan" (at the Pierpont Morgan Library, New York) and the fragment "Sanditon" (at King's College, Cambridge), the only other autograph novel manuscript of comparable length.

"This unique manuscript provides scholars with important evidence, not just of how Jane Austen composed and revised her work, but also of how her other manuscripts must have looked before they were edited by her publishers," said Gabriel Heaton, Sotheby's Senior Specialist, Books & Manuscripts Department.

"The Watsons is quintessential Jane Austen in style and the influence of this novel on her later works can be clearly seen."

The Watsons centres on a family of four sisters, the daughters of a widowed clergyman. Its heroine is Emma, the youngest, who has been brought up by a wealthy aunt. When her aunt contracts a foolish second marriage, Emma is obliged to return to her father's house and endure the crude husband-hunting of her two 20-something sisters.

She has, however, a close relationship with her eldest and most responsible sister Elizabeth. The Watsons contains many of Austen's perennial themes and her genius for shrewd social observation.

The novel is considered to be around a quarter complete. The manuscript comprises 68 hand-trimmed pages, split into 11 loose gatherings penned in Austen's tiny, precise hand and heavily worked through with revisions.

The novel was written at a time when Austen was not yet a published writer but during a period in her career that is considered to be her mature writing period.

The work is well known to Austen scholars and has been acclaimed by modern critics, including Margaret Drabble who described it as "a tantalizing, delightful and highly accomplished fragment, which must surely have proved the equal of her other six novels, had she finished it."