Re "blacks are decendants of Cain"
I was raised in a non-Mormon protestant church in which we were also taught this.

From Christianity and History: Bible, Race & Slavery
Repression and Superiority

The later repression and discrimination against the freed black slaves received as much biblical and Christian support as the earlier institution of slavery itself. This discrimination and the choice to enslave blacks only was made primarily on the basis of what has become known as the "sin of Ham" or "the curse of Canaan." Occasionally there would also be defenses of the inferiority of blacks by asserting that they bore the "mark of Cain."

The rest of that essay is worth reading, if you are interested in a wider view of the use of scriptures to validate racism.

rags