Funny! No one looked into books concerned with the railroads. Here is the definition from "Long Steel Rail."
Tarrier: "19th century hard-rock laborers who drilled and blasted their way across the continent paving the way for the railroad tracks." Norm Cohen, 1981, "Long Steel Rail," p. 555.
Cohen goes on to say the origin is uncertain, but he favors terrier; these dogs dig their quarry out of holes.