The Irish on the Somme.
This is the stuff of which early ethnography was made, back in the days when ethnic habits were mistaken for racial characteristics; indeed, this 1917 book could be considered an extension of MacDonagh’s 1898 work, Irish Life and Character. If you can tolerate the author’s use of stereotypical 18th- and 19th-century “stage Irish” dialect, you’ll find accounts of the exploits of the Irish units which served in the Battle of the Somme, along with the usual kinds of stories about trench life, mingled with the author’s observations on Irish culture.
Genealogists and others interested in looking for soldiers of Irish descent who served in other British Army units may find John Redmond’s introduction helpful: in it he lists more than thirty regiments in which 225 Irish surnames appeared in a casualty list dated November 1, 1916.
This book has been issued for sale in the the binding pictured above, but it is in the public domain, and along with other works by MacDonagh is available for free download, at sites such as the Internet Archive and Project Gutenberg.