I believe this actually means that a Continental drift occurred. Making the same found in one continent, also seen in another Continent.
A- Trade
Explanation
(The internet told me so:))
The slave trade grew rapidly during the exploration and exploitation of the Americas due to the demand for cheap labor.
The age of exploration resulted in European countries establishing permanent settlements in different parts of the New World. When establishing these settlements, the explorers encountered new goods and products that would become extremely valuable in European society. In order to maximize their profits on these goods, the colonizers needed a lot of labor. This resulted in several deals made between European leaders and African leaders who were willing to sell their own people into slavery.
The system of slavery would allow for cheap labor and a huge increase in profits for several European countries.
What I can infer from what Lewis and Clark saw when moving west from the Mississippi river is that the landscape along the river changed drasticallly. The forest receded, replaced first by the high prairie and then the shorter grass of the high plains. The temperatures became colder and as they continued their expedition by the river they realized that there was no water route to the pacific ocean, just more mountains.
