The isthmus connecting the Tasman Peninsula to Tasmania is covered in a pattern of regular rectangular saltwater pools. Although these depressions look distinctly manmade, they are the result of a rare type of natural erosion.

Occurring near sea coasts on flat rock which has broken into regular blocks, the effect is known as “tessellated pavement” for its resemblance to Roman mosaic floors (also called tessellated pavement). The pavement takes two forms. Depressions are known as pan formations, occurring when saltwater wears away the center portion of the stones into pools. The opposite effect is known as a loaf formation, when the edges of the stone are worn away leaving a rounded crown resembling rising bread.

Tessellated pavement is extremely rare, found only in a few places on Earth. The geology is not related to the effect that created the Giant’s Causeway in Northern Ireland and Fingal’s Cave in Scotland. Those features were formed as basaltic lava cooled and fractured; tessellated pavement occurs as sedimentary rock erodes.

Eaglehawk Neck is also famous for its association with the prison colony at Port Arthur. In 1832, a military outpost was setup to watch for escaping prisoners, and dogs were positioned along the isthmus to raise a ruckus if they spotted an escapee. The motley army of dogs were described in 1840:

“There were the black, the white, the brindle, the grey and the grisly, the rough and the smooth, the crop-eared and the lop-eared, the gaunt and the grim. Every four-footed, black-fanged individual among them would have taken first prize in his own class for ugliness and ferocity at any show.”

Port Arthur closed in 1877 (it’s now open as a tourist attraction), but there is a monument to the dogs at Eaglehawk Neck. Along with the tessellated pavement, there are several other unusual geologic formations, including a natural arch and blowhole nearby.