Although the title suggests a memoir of time spent in Africa, Impressions of Africa is nothing of the kind. It has nothing to do with any real place called "Africa." Instead, it is a fantasy novel, full of fantastic anecdotes, bizzarre events, and improbable coincidences piled one on another to the point of tedium. It begins with a strange pageant, which begins with the proclamation of the emperor, Talou VII, and the execution of some enemies of the state. There follows a series of extraordinary performances. Among them: a marksman shoots the white off a soft-boiled egg while leaving the still-liquid yolk perfectly intact, a trained worm plays the zither by making drops of a special dense water fall accurately on the strings, a man with a particularly wide mouth has trained himself to sing four-part harmony with each part coming from a different part of his mouth, a talking horse articulates words perfectly but without understanding, etc. etc. All the performances are incredible and perfect (except that of a celebrated ex-ballerina, now obese, who takes a tumble). The account of this pageant takes up nearly half the book.
The second half of the book backtracks to give the history and preparations for the pageant. We learn that the performers were passengers on a ship bound for South America which was wrecked, and they are being held for ransom in this "African" kingdom. While waiting for ransom money to arrive from Europe, they prepare their preposterous acts. At the same time, we are told something of the history of the country: how the emperor (who appears in drag) was betrayed by his wife who two-timed him with a minister and abandoned the emperor's (and her) daughter in the woods. Then, when the daughter, now grown up, reappeared, she blinded her. (Happily, her sight is restored later.) We also learn how the rival kingdom to the south is finally conquered and the two kingdoms, long divided, are united. The narrative is frequently interrupted by anecdotes and digressions, many of them accounts of how a wife betrays her husband with a secret lover which whom she escapes (or doesn't escape). Eventually, the ransom money arrives. The emperor is proclaimed, his unfaithful wife, the minister, and several other bad guys are put to hideous deaths, and the pageant takes place. All this was described at the beginning, of course, so the book has the form of a circle, in which we are presented with some events, then an account of the background of those events, which brings us eventually back to the beginning. At the very end, the shipwrecked passengers return to Europe.
Roussel experimented with literary effects and had admirers among a few twentieth-century French writers. I have not read any of his other books, but my impression is that his reputation as an avant garde writer must rest on other works, not on Impressions of Africa, although it is true that the events described at the beginning of the book take on a different color if one re-reads them after having finished the book. Still, I found the writing undistinguished and the endless series of preposterous anecdotes tiresome. Unless you are an inveterate fan of Grimm's Fairy Tales I think you can skip this one.