Who is Silas Stone from March and what is their importance?

Silas Stone was the young soldier who was sent to assist March in collecting bodies at the opening of the novel. While the men search, they are fired on by the enemy and forced to leap over a cliff into the river below. Note, Silas cannot swim. In the end, March is not able to save Stone, but he is left with a torn patch of Stone's wet jacket in his hand to remember him.