There have been a variety of materials used in the past to construct grave markers. It is clear from the data that throughout the 19th century marble was the most popular stone. At about 1900 we see a shift in construction material to granite. It is gradual and takes several decades, but by the 1950's, granite is used almost exclusively. Marble is a softer stone, and tends to wear more easily, where as granite is much harder.
Marble is, when it is new, a very attractive stone, but wears terribly.
The granite markers, on the other hand, while perhaps not quite as pleasing to the eye, look today exactly the same as the day they were placed. It is possible that people today are more concerned about leaving some kind of permanent mark on the world in death if they cannot do so in life. Size I expected initially to see the average volume of material used in the construction of stones increase toward the present, and was surprised to see a fairly constant average stone volume since the late 1800's. I am hesitant to consider the data I collected for stones dating to before the Civil War because, but for a few exceptions, these stones belong to wealthy, important members of society. Several of the earliest grave markers belong to original Vestrymen of the church, and other dignified personages such as Sarah McCarty, daughter of George Mason, Jeremiah Bronaugh, cousin of George Mason, and the first U.S. Surgeon General, doctor to George Washington, William Brown.