Disk

A disk is a terrain feature consisting of a naturally generated roughly circular deposit of a soil-like block under or next to bodies of water.

Description
Disks are generated at the Euclidean distance n (i.e. x2+y2=n) from a given central block, creating a circular-looking pattern of the given block with a radius of n. They are commonly seen throughout rivers, and can also occasionally generate with small water lakes.

ID
As this is a terrain feature as opposed to a structure, its ID is namespaced.