Randolph B. Marcy,
The Prairie Traveller, a Hand-book for Overland Expeditions…
(1859)
“ The men who can not swim are then mounted upon the best swimming horses and tied on, otherwise they are liable to become frightened, lose their balance, and be carried away in a rapid current; or a horse may stumble and throw his rider. After the horses have been strung out in a single line by their riders, and every thing is in readiness, the first horse is led carefully into the water, while the men on the opposite bank, pulling upon the rope, thus direct him across, and, if necessary, aid him in stemming the current. ”
