Auchagach’s maps were, of their type, quite good, but by the time his water system made it onto Bellin’s map, it was far from reality. Auchagach’s maps had neither orientation nor scale indicated and Bellin erred in both these aspects when he copied them to his map. The actual river systems to the northwest of Lake Superior have a much more Northwest-Southeast orientation than the almost straight West-to-East alignment shown by Bellin, and Bellin shows the river systems as much larger than they are in reality. While Bellin does not show a definite Pacific coast in the west, his River of the West extends very close to wherever that coast would be, presenting what appears to be an easy water route to the Pacific. As good as this looked on Bellin's map, failed French attempts in pursuing this route to the Pacific in the following years soon demonstrated the fallacy of Bellin’s depiction.
“I discovered recently a river flowing to the west... That the river appeared to go, according to the compass, south west by south...the lower part may go to the sea to the south west by west.”That is, the river may flow to the Pacific Ocean.
According to a scholarly study, the Vérendrye sons had probably visited a Hidatsa village [though the names are similar, the Mantannes were almost certainly not Mandans, as they are often thought to be]. The village was located just south of the conjunction of the Little Knife River with the Missouri, on a part of the Missouri where it looks like the river flows south/southwest. The perceived direction of the river flow, combined with information gathered from conversations with the Indians interpreted through the lens of their hopes, led the Vérendryes to conclude the river might be the much desired River of the West. Philippe Buache included his take on their "discovery" in his 1754 map of western New France shown above.
Buache tried to merge this Vérendrye information with previous beliefs, so he has another river, which flows out of a "L. du Brochet," merge with the dotted-line River of the West [this coming from Delisle's 1722 map shown in the previous blog] and this river in turn flows into our old friend the Sea of the West.
Basically, the French were still confused, not sure if there was a Sea of the West, River of the West, or some other water route to take them from the Great Lakes to the Pacific. Unfortunately for them, they were never able to figure it out, for as a result of the French & Indian War, in 1763, they gave up all their possessions in New France to the British.