When rocks break from Jacobsville cliffs, they are angular pieces, and it takes wave action to round them.
The Keweenaw Bay shorelines have many cliff exposures of Jacobsville Sandstone.
Jacobsville cobbles are quite variable and usually multicolored.
Sandstone is made of sand particles. Sand particles range in diameter from 0.0625mm (or 1⁄16 mm, or 62.5 micrometers) to 2 millimeters.
The red portions of the sandstone are rusted (oxidized) by groundwater that flowed through the rock.
In the Keweenaw sandstones are reddish or rusty, with white layers and spots. They tend to form flat pebbles and cobbles