These ingredients act as files in the hand of a workman, and grind, polish, and reduce the rocks against which they are borne.
"Geology"
James Geikie
And while the latter is being gradually reduced, the stones and grit which act as the files are themselves worn and reduced; so that stones diminish in size, and grit passes into fine sand and mud, as they move from higher to lower levels.
"Geology"
James Geikie
For miles along and around the same track where I walked, single files of men were plodding along, their grey figures silhouetted where they tramped on the skyline, with capes blowing and steel hats shining.
"From Bapaume to Passchendaele, 1917"
Philip Gibbs