that C on his arm denotes he was in 2nd Bn Seaforth Highlanders. According to Osprey book on British Battle Insignia 1914-1918 by Mike Chappell. I think he needs a patch of MacKenzie tartan above it. you can just see the C on these chaps arms in this picture. Roll Call of the 2nd Battalion, The Seaforth Highlanders on the afternoon of the first day of the Battle of the Somme near Beaumont Hamel. They are wearing the haversack, rolled groundsheet and mess tin instead of the large pack. The insignia on their sleeves indicates that they were part of the attacking force.
