Scholars are aware of numerous ancient document burials in stone boxes, and of many ancient texts, religious and otherwise, that are inscribed upon metal plates.  Some critics have described “reformed Egyptian” as a mythical language that never existed.  John Tvedtnes (formerly a member of the staff of the Maxwell Institute at BYU) published “The Book of Mormon and Other Hidden Books,” in which he discusses specific examples of such writings and such burials from across the ancient and medieval Near East.  For an accessible discussion of these and other interesting related topics, see John A. Tvedtnes’ “Ancient Texts in Support of the Book of Mormon,” in Donald W. Parry, Daniel C. Peterson and John W. Welch’s “Echoes and Evidences of the Book of Mormon”