Geographic factors that encouraged the growth of slavery between 1607 & 1775?

Question

Okay. This is for AP US History... So this is supposed to be a college level essay. I have all the info I need, except for one or two more points about the GEOGRAPHIC factors.
Here is the whole Question:
How did economic, geographic, and social factors encourage the growth of slavery as an important part of the economy of the southern colonies between 1607 and 1775?

I have more than enough stuff for economic, and a passable amount for social, but I NEED more geographic points.
So far all I have is that not all of the staple food crops were compatable with the southern soil and slaves knew how to grow rice. They didn't contract diseases from the insects in the rice fields, either.

Is what I have so far correct for the geographic part? I need just one or two more points for this! Then I can write my amazing essay for a good grade. = )

Okay... and one more social factor would be nice. = )
I have that the more slaves a person had, the more wealthy they were viewed as. The elite of the south enjoyed being at the top of the social ladder. The land- and slave-owners of the south were the "winners" of society, and the poor farmers and slaves were the "losers." Because while the poor farmers were free, they had to work just as hard.

Any more suggestions? I'm just stuck in a rut here. = / I love history, but sometimes I get so angry with my book. It doesn't always give me answers. = (
And before anyone suggests it, I've googled it. Thats where I got most of my social aspects. I got all my economic [and some social] points from the book [gasp!].
Its just no one seems to want to concentrate on the geographic!!!

Answer 1

One example: the delta in Louisiana is a large flat expanse that is self-watering and contains the richest soil available. This led to the ability to plant huge plantations of sugar and cotton, which needed slave labor in order to be functional. That's one example. Not as rich but also similar geography is Mississippi, also home to development of huge plantations for mostly cotton.

You should be able to think of more, but I believe that should qualify. Look for areas where there weren't expansive areas suitable for plantations.