He saw a whitish dawn with much mist floating over the fields, and he believed that a large river, probably the Marne, must be near.
As far as he could see the ground was covered with German soldiers.

They too had dropped at the command to stop, and had gone to sleep as they were falling.

The majority of them still slept.
"What is it, Fleury?
Why did you wake me up ?" asked John.
"The river Marne is close by, and I'm sure that the Germans are going to retreat across it.

I had an idea that possibly we might escape while there's so much mist.

They can't watch us very closely while they have so much else to do, and doubtless they would care but little if some of us did escape." "We'll certainly look for the chance.