Back again.
I have just picked up the further info you have sent. I am absolutely amazed at what you have found out for me. When I get back I can look into where George Horner was in 1915 and beyond. I will also look at the books I have on WW1 and the Somme in particular to see if I can pick up some of the units you have mentioned and where they were, what they did etc.
A few other snippets. Of the post cards he sent 4 are numbered in pencil and in No 6, at the end of the message he states, "this is the last of the mine cards." Of those 6, the 4 I have (Nos 2, 4, 5, & 6), are postcards of mines and they are La Bassee, Grenay, Les Brebis Bully-Les-Mines and Mazingarbe. He also signs himself Joe, a name I never knew him by, he was always called George as far as I can recall.
In my ignorance of investigating further I'm not sure what else you can do for me. What you have done has given me a great deal to get on with and I am extremely grateful
Regards,
Ken