Armored mud ball

[4][2] Under circumstances of rapid burial, armored mud balls can become incorporated into other sediments which subsequently form sedimentary rocks.

[6] However, because the pebbles that protect them are not spread evenly throughout the clay body, but are found only on the outer surface, the name 'armored mud ball' was proposed in 1940 by geologist Hugh Stevens Bell, and has since been widely adopted.

[11][3] In the early 20th century, James Gardner hypothesized that these structures formed by the accumulation of fine clay particles as they flowed along a stream, gradually building up concentric rings of sediments by adhesion until their weight eventually stopped them rolling with the current.

[3][12] That view held sway for some 20 years, despite an earlier suggestion in 1875 by Jones and King that those mud balls found on beaches had formed from broken off fragments of clay from adjacent cliffs which had then been rolled by wave action.

[8] A total of 25 armored mud balls were found in quarried sandstone blocks that used to serve as cable anchors for a now-defunct suspension bridge over the Connecticut River.

[14] The examples from the Connecticut River Valley of Western Massachusetts are particularly notable because they are among the most well-preserved and easily accessible lithified armored mud balls in the world.