A ledge
A narrow shelf is often called a "slim shelf" or a "slender shelf".
A ledge.
The edge is called the shelf break. The actual declining shelf is called the called the continental slope.
A long, narrow and curled bone shelf which protrudes into the breathing passage of the nose is called a turbinate, or better known in anatomy as a nasal concha.
shelf
This is because it is a narrow boat
A long narrow cut is called a slit.
The continental shelf layer is called the shelf break. It is the steepest part of the continental shelf where the seafloor drops off sharply towards the deeper ocean floor.
A wooded ravine is called a gully.
Some small narrow boats are called canoes, others are called kayaks.
Some small narrow boats are called canoes, others are called kayaks.
A narrow passage through land is called a gorge.