That's what I was thinking but it does say on WIKI that Barred Rocks are a hybrid.
The Plymouth Rock was first shown in
Boston in 1849, but was then not seen for another twenty years.
[2] In 1869, in
Worcester, Massachusetts, one D.A. Upham
cross-bred some
Black Java hens with a cock with barred plumage and a single comb; he
selectively bred for barred plumage and clean (featherless) legs.
[6]: 68 His birds were shown in Worcester in 1869; the modern Plymouth Rock is thought to derive from them.
[2] Other people have been associated with the development of the Plymouth Rock, as have other chicken breeds including the
Brahma, the
Cochin (both white and buff), the
Dominique, and the
White-faced Black Spanish.
[2] According to the
Livestock Conservancy, it originated from
cross-breeding of
Java birds with single-combed Dominiques;
[7] or, based on
genomic analysis, principally from the Dominique, with substantial contribution from the Java and Cochin and some input from other breeds.
[8][9]