I had never considered the religion of the Africans who were brought to America as slaves. I simply assumed that they practiced one of the many indigenous primal religions (this was a common assumption by scholars for decades, according to Diana Eck).
In truth, some 10% of the West Africans who were forced into the slave trade were Muslim, (Eck, p. 240). This created interesting tensions, as the African Muslims were often literate, leading to their classification as Arabs instead of Africans (slaveowners presumed that Africans could never be literate). We have some of the writings of these Muslim slaves, as well as their masters, which must make for fascinating historical reading. Middle Eastern Muslims came to America as early the 1870s, and Muslims were working for Henry Ford. All of this underscores Eck's larger point of America (and, in many ways, the larger world) being quite religiously diverse, the popular imagination and stereotypes to the contrary.
The African Muslims must have been most curious to the slavemasters (if they bothered to notice). They did not pray to or in the name of Jesus, but neither were they superstitious or polytheists (although some Christians misunderstood them and thought they worshipped the prophet Muhammed). There are affinities between Protestantism and Islam, with the stress on a written sacred text and a sovereign, transcendent God, along with an avoidance of things sacramental, superstitious, and priestly. Sadly, these interesting similarities built no bridges.