Lieutenant Symons does not state whether any confusion ever arose as a consequence of the fact that three of his five Indians bore the inevitable French-Canadian name of "Pierre." Of the method of work followed by himself and his topographical assistant, Downing, throughout the voyage, he writes:
"Mr. Downing and myself worked independently in getting as thorough knowledge of the river as possible, he taking the courses with a prismatic compass, and estimating distances by the eye, and sketching in the topographical features of the surrounding country, while I estimated also the distances to marked points, and paid particular attention to the bed of the river, sounding wherever there were any indications of shallowness. Each evening we compared notes as to distances, and we found them to come out very well together, the greatest difference being six and three-fourths miles in a day's run of sixty-four miles. Some days they were identical. The total distance from our starting point ... to the mouth of the Snake River was estimated by Mr. Downing to be three hundred and sixty-three miles, and by myself to be three hundred and fifty. His distances were obtained by estimating how far it was to some marked point ahead, and correcting it when the point was reached; mine by the time required to pass over the distances, in which the elements considered were the swiftness of the current and the labour of the oarsmen."
I may state that it was only rarely that we found the distances arrived at by Lieutenant Symons and Mr. Downing to be greatly at variance with those established by later surveys. In the matter of bars, rapids, currents, channels and similar things, there appeared to have been astonishingly little change in the four decades that had elapsed since he had made his observations. Where he advised, for instance, taking the right-hand in preference to the middle or left-hand channels, it was not often that we went far wrong in heeding the direction. Bars of gravel, of course, shift from season to season, but reefs and projections of the native rock are rarely altered by more than a negligible erosion. The prominent topographical features--cliffs, headlands, _coulees_, mountains--are immutable, and for mile after mile, bend after bend, we picked them up just as Symons reported them.