Chasms

Chasms are large trenches in the ground that appear commonly in Corrupted areas. The depth of chasms seems to vary greatly; they can be very shallow and only drop down 100 ft. or so, or they can be very deep. Chasms commonly have Demon Altars and Shadow Orbs at the bottom which are only found in such chasms, often accompanied by chests and pools of water.

Chasms are made entirely out of Ebonstone.

You have to use Dynamite or Purification Powder to get to the Shadow Orb. If you don't have such means, a Demonite Pickaxe can also be used to mine Ebonstone.