The assault phase of the Battle of the Somme commenced 10 minutes after the blowing of the Hawthorne mine. The original black and white footage is from a full-length, silent documentary film, The Battle Of The Somme (1916). That film has been digitized and set back to the original camera speed (something I worried about back here). Watch the original film here. It's lengthy, but worth it.
A couple years ago, two amateur filmmakers skilfully blended past and present cinematography. You won't realize what they've done for a minute or so but then it's incredible! The film is poignant too: Most of these men would be dead 40 minutes after this film was made.