While Indy may be known as the Brickyard, the very first iteration of the track surface in the spring and summer of 1909 consisted of a 2-inch-thick layer of creek gravel, a 2-inch layer of crushed limestone and a layer of taroid. That was followed by a half-inch layer of stone chips mixed with larger stones. That was topped with another layer of taroid (a coal-tar preparation) with stone dust worked into the surface.
In the fall 1909, a two-inch layer of sand was put down, then 3.2 million road-paving bricks were placed. There was roughly a quarter of an inch between each brick. After the surface was leveled, a concrete was poured between the bricks to hold things in place.
That brick surface lasted more than 50 years. In 1961, nearly the entire track surface was covered with asphalt, leaving just a three-foot strip of bricks at the start/finish line. That strip remains there to this day. In 1976, the entire track was cleared and resurfaced for the first time since 1909. Further track work took place in 1988, 1995, 2002 and 2004 — the core sample reflects eight layers in all, but of course doesn't reflect material that was removed. The last round of work included the pit and warm-up lanes, too.