The compound sibilants may also be expressed not by single signs, but by the combinations tsh and dzh; although, for certain reasons, such a mode of spelling is inconvenient.
"The English Language"
Robert Gordon Latham
Ch commonly represents the compound sound of tsh; as in church.
"The Grammar of English Grammars"
Goold Brown
Ch is generally sounded like tch, or tsh, which is the same to the ear; as in church, chance, child.
"The Grammar of English Grammars"
Goold Brown