Of the coast early knowledge was acquired for geography; but where the continent broadens out either north or south, making the interior inaccessible for trade purposes with the coasts, ignorance remained even down to the present century.

Even to the present day the country south of the valley of the Amazon is perhaps as little known as any portion of the earth's surface, while, as we have seen, it was not till the early years of this century that any knowledge was acquired of the huge tract of country between the Mississippi and the Rocky Mountains.
It was the natural expansion of the United States, rendered possible by the cession of this tract to the States by Napoleon in 1803, that brought it within the knowledge of all.

That expansion was chiefly due to the improved methods of communication which steam has given to mankind only within this century.

But for this the region east of the Rocky Mountains would possibly be as little known to Europeans, even at the present day, as the Soudan or Somaliland.

It is owing to this natural expansion of the States, and in minor measure of Canada, that few great names of geographical explorers are connected with our knowledge of the interior of North America.