“You chop down big trees, I suppose,” said Mr. Stewart.

“Pretty big,” I said. “I cut my foot with the ax once when I was new at it.”

Finally, there wasn’t any way out of it but for me to take off my shoe and show them the scar, and roll up my trouser-leg and exhibit the two white marks the horse’s caulks had left.

Does he want to say “caulk shoes”, like horseshoes ? And can you find me any definition of what a horse’s caulk shoe is ?

Some horseshoes have “caulkins”, “caulks”, or “calks”: protrusions at the toe and/or heels of the shoe, to provide additional traction.