If you are short on time, these resources are your best bet for this topic:
The Campaign of the Marne by Decisive series of engagements fought between Paris and Verdun along the Marne River during the German invasion of France in September 1914.
taken from Spencer C. Tucker et al., eds., World War I Encyclopedia: Volume III: M-R (Santa Barbara: ABC-CLIO, 2005): 747.
Photo take from the National World War I Museum http://theworldwar.pastperfect-online.com/35156cgi/mweb.exe?request=record;id=84A3A9E7-7D76-4B59-A58B-208789424726;type=102
Caption on back of image: ”Heroes of the Marne Earn Well Deserved Rest. Never was the indomitable spirit of the French soldiers shown to better advantage than when the first great drive was made on Paris. Spurred on by cheerful talk of their officers, these men created history by their defense of their mother land. The picture shows a regiment of those fighters returning to billet after a long stretch in the trenches.”