Actually, let me correct this. Joseph Smith actually indicated the 10 tribes were no longer on the Earth and would return one day from the North countries when they return.
President Young said he heard Joseph Smith say that the Ten Tribes of Israel were on a Portion of Land separated from this Earth.
- Prophet Wilford Woodruff, Wilford Woodruff’s Journal, September 8, 1867, reprinted in Susan Staker, ed., Waiting for World’s End, The Diaries of Wilford Woodruff, 1993, p. 291
10. We believe in the literal gathering of Israel and in the restoration of the Ten Tribes; that Zion (the New Jerusalem) will be built upon the American continent; that Christ will reign personally upon the earth; and, that the earth will be renewed and receive its paradisiacal glory. Articles of Faith, verse 10.
James E. Talmage; In his book Articles of Faith, page 340, "—it is plain that, while many of those belonging to the ten tribes were diffused among the nations, a sufficient number to justify the retention of the original name were led away as a body, and are now in existence some place where the Lord has hidden them’.
3 Nephi 16:1 And verily, verily, I say unto you that I have other sheep, which are not of this land, neither of the land of Jerusalem, neither in any parts of that land round about whither I have been to minister.
3 Nephi 16:2 For they of whom I speak are they who have not as yet heard my voice; neither have I at any time manifested myself unto them.
3 Nephi 16:3 But I have received a commandment of the Father that I shall go unto them, and that they shall hear my voice, and shall be numbered among my sheep, that there shall be one fold and one shepherd; therefore I go to show myself unto them.
This has actually been part of Mormon lore for a very long time. Also, one of the signs that this day is fast approaching was to be the ice caps melting. Hmmmm, I see no signs of that. Do you?