• If the stone is flat-topped hard marble, dates are about 1830-1849.
• If the "mystery" stone is round or pointed soft marble with cursive inscriptions, look for a date of 1845-1868.
• Masonic four-sided stones began in 1850 and are still in use today.
• Pylons, columns and all exotic-style monuments are usually dated 1860-1900.
• Zinc monuments date from 1870-1900.
• Granite, now common, came into use about 1900.

If the writing is too faded to read, use a 75 watt black light bulb in any lamp that casts light directly on the written message. The writing will miraculously appear.

Also see: http://www.gravestonestudies.org