After an intense study of all the doctrines the Book of Mormon reveals which are not found in the Bible, Elder B. H. Roberts concluded: “Beyond controversy neither the native intelligence nor learning of Joseph Smith can possibly be regarded as equal to such a performance as bringing forth the knowledge which the Book of Mormon imparts upon these profound subjects; nor can the intelligence or learning of those who assisted him in translating the book be regarded as sufficient for such a task. Nor was the intelligence and learning of any one to whom the origin of the book has ever been ascribed equal to such an achievement. Indeed the book sounds depths on these subjects not only beyond the intelligence and learning of this small group of men referred to, but beyond the intelligence and learning of the age itself in which it came forth.”

New Witness for God, 3 vols. (1909), 3:230

Also quoted page 54 of Oct. 2006 Ensign.