The fourth number of this very remarkable work has been published; and we have had a fair opportunity of testing the merits of the mysterious author. The circumstances must now be generally known, under which these works appear before the public. It appears that MUNDT, a German scholar, who is publishing a continuation of SCHLEGEL'S History of Literature, has in his delineations of character given almost unbounded praise to an American named SEATSFIELD. Among the various works attributed to him are 'Life in the New World,' 'Sea, Sketches,' 'South and North,' 'Virey,' the 'Legitimate,' and others, which are to be issued in rapid succession from the press of WINCHESTER, 'the indefatigable,' as he may well be called; for the rapidity with which he sends out to the world the literary novelties of the day is a theme of public marvel. The German, in which these volumes are written, is said by competent judges, to be very pure and powerful: and indeed we may rest assured that if the case were otherwise, a critic of such high reputation as MUNDT would never have spoken of SEATSFIELD in such enthusiastic terms. The publisher, we understand, obtained several of the works from the library of Columbia College, through the politeness of Professor TELLKAMPT. The opinion, which some have expressed, that SEATSFIELD'S books are made up of stolen selections from different American writers, is unfounded. We cannot recognize in his style or thought familiar passages; and beside, there does not appear to be any rational inducement for this species of plagiarism. It is evident that the writings are indeed what they appear to be, the genuine productions of an able man. The descriptions of natural scenery are very graphic. 'The first trip on the Red River,' and the description of the trappers, is one of the most animated sketches we have ever read. Our mountains, rivers, cataracts, ocean-lakes, and forests, are described with the most remarkable spirit and truth.' The translation, we are informed by the best judges, is extremely faithful. POETRY AND HISTORY OF WYOMING. By WILLIAM L. STONE, Esq. Second edition, enlarged. New-York: MARK H. NEWMAN.