From the earliest days of the discovery of North America, there was the hope for a relatively easy water route across the continent. As the vast width of the continent became clear, various speculations of rivers flowing west from the middle of the continent were put forward, as well as some theories about a large “sea of the west” (also known as the “Mer de l’Ouest”) located in the northwest and reaching well into the interior. No such inland sea exists in continent, but there were some which appeared on maps for over a century.
One of the most respected cartographers around the turn of the eighteenth century was Guillaume Delisle, who took particular care in trying to use authentic sources to produce accurate maps. In grappling with the geography of North America, Delisle read the Jesuit Relations of 1669, which included Indian reports which seemed to indicate that there was a large inland lake in the northwest part of the continent. This belief was supported by a 1625 report by one Juan de Fuca, who said that in 1592 he had found a bay on the American Pacific coast, between 47 and 48 degrees, which he sailed into, finding a large sea which led far to the east. With these two pieces of evidence, between 1695 and 1700 Delisle drew some manuscript maps of North America showing a large Mer de l’Ouest. He obviously had doubts about this, however, for none of his printed maps ever shows this sea.
Delisle’s Sea of the West did, however, find a believer in another French cartographer, Jean Baptiste Nolin, who in 1700 produced a double hemisphere world map showing this sea, a rendering which was soon picked up by Dutch publishers Covens & Mortier for their world maps a few years later. Other cartographers followed these maps with their own versions. Delisle actually sued Nolin for copyright infringement, winning his case and forcing Nolin to remove all examples of this “offending geography” from his plates and also to destroy all copies of the wall map with the original sea on them (only three copies of this map have survived. With this and a lack of support from evidence, this original Sea of the West faded towards to the middle of the century.
However, like any good cartographic myth, the Sea of the West was not so easily done away with. In 1750 the sea made a reappearance, revived by Philippe Buache and J.N. Delisle (Guillaume’s half-brother). This revival was the result a letter, which appeared in 1708, purporting to be written by a Spanish Admiral, Bartholemew de Fonte, who wrote that he had sailed inland along the Pacific Northwest Coast, sailing through a series of bays and rivers until he met a ship which had sailed west from Hudson’s Bay. This letter was, in fact, a total hoax, but it was believed by Buache and J.N. Delisle, so they resurrected the Sea of the West.
With their connections to Guillaume Delisle (Buache was married to Guillaume’s sister), their new Sea of the West flourished on a number of maps over the next few decades. However, the explorations of the northwest coast by George Vancouver and James Cook in the late 1770s provided good evidence that there was no such inland sea and once again the Sea of the West began to disappear from maps, though it did survive on some into the early 19th century.
See maps showing the Sea of the West