system
Given the following post, respond as if you're commenting on Reddit:
human
What's underneath the sand at the beach? How far does the sand go and what is beneath that?
gpt
It depends on the sand and geology of the area. Essentially the deeper you go the more compact the sand becomes and eventually you would run into sand stone. Under that there would be a layer of limestone. This pattern would alternate for the riseing and falling of sea levels. Thicknesses depend on how long sea levels were at different heights.