The majority of the map is made up of stone, which can be removed with tools.
When a stone block is removed, the (background) texture for that block is replaced with the "removed stone" texture:
There are three types of Treasure Block distributed throughout the map. The deeper you dig, the more frequent these are.
When any Treasure Block is removed, the (background) texture for that block is replaced with the "removed treasure" texture:
Artifact Blocks yield Artifacts, which are human-made objects from different civilizations. (See Artifacts).
Fossil Blocks yield Fossils, which include various bones, fossils, and other animal remains and objects. Amber, petrified wood, fossilized footprints, and dinosaur eggs would also fit into this category. (See Artifacts).
Mineral Blocks yield Minerals, which include gemstones, precious metals, and other interesting mineralogical objects.
The top level of the map is made up of Dirt Blocks and (on the top layer) Grass Blocks. These blocks can be removed for "free" with the pickaxe, meaning to math problem must be solved.
There's a chance of a Plant appearing on the top of a Grass Block.
When a Grass Block is removed, the (background) texture for that block is changed to the "removed grass" texture, and any Plants above it are removed.
When a Dirt Block is removed, the (background) texture for that block is changed to the "removed dirt" texture.
The bottom boundary of the map is marked with Mantle Stone, which is always unbreakable by any tool.
The top layer is Mantle Stone 1, which transitions from Stone Blocks.
The second layer of Mantle Stone is made up of Mantle Stone 2.
The third and all lower layers of Mantle Stone are made up of Mantle Stone 3.