The focus of this anthology is a little vague; Silverberg woozily sums up the nine stories as ""eight realms of the imagination. . . lost worlds and unknown horizons of the mind."" But any collection that affords a chance to reread H. G. Wells' ""The Country of the Blind"" should be welcomed on that account alone. The most recent contributions, next to Silverberg's own ""Trips,"" are Jack Finney's wistful 1950 yarn of a time-traveling train on ""The Third Level"" of Grand Central Station and a 1942 Leiber story in the Fafhrd and Gray Mouser series. The rest are considerably earlier, including Poe's ""A Tale of the Ragged Mountains,"" a time-dislocation story by the almost forgotten Olivet Onions, an intriguing oddity about vegetable intelligence written for the New York Sun by Edward Page Mitchell, and vintage purple palpitations by Lovecraft and Clark Ashton Smith. True, the whole is not one of Silverberg's most inspired mixtures in terms of selections striking sparks off each other. But item by item, it could hardly be outdone.