Complex sentence: Joseph Smith, the founder of Mormonism, has also appeared: his face hidden by a hat, a reference to Smith supposedly reading seeing stones by putting them inside a stovepipe hat and sticking his face inside.
Split into simpler sentences: Joseph Smith, the founder of Mormonism, has also appeared. His face is hidden by a hat, a reference to Smith supposedly reading seeing stones by putting them inside a stovepipe hat and sticking his face inside.