Julien Gracq's novel ''Au château d'Argol° includes a chapter in which one of the heroes, Herminien, discovers a chapel hidden deep within a forest. ''Soon ... through the branches, twisted in fantastic arabesques, appeared the grey wall of a chapel hanging in the midst of an abyss.'' He sees an organ there, and, climbing the steps of the loft, he starts to improvise. ''Then, from the depts of his disquiet, a sound rose up.'' The author gives a description of this improvisation that, musically, expresses all the psychological tension that has built up in the course of the novel. The musical work bearing the title of this chapter does not claim to respond the letter of the literary description of this improvisation, which would be as impossible as describing Proust's ''Sonate de Vinteuil'', but it is inspired by both - this description and by the novel itself.