One way to figure out the era your ancestor was buried is to examine the material from which the tombstone is made.  If your ancestor has a stone made of slate or common fieldstone (except wood used by pioneer) chances are the stone dates from 1796-1830.

If the stone is flat topped hard marble, dates are about 1830-1849.

If your 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 appear miraculously.