La Poblacion Negra de Mexico by Gonzalo Aguirre Beltran
From the jacket (rought translation):
The first edition of this book, only six years after the expansion continent-wide of the indigenist movement born in Mexico, was a rediscovery for this part of the Americas. It demonstrated that in Mexico's veins ran not only indigenous blood that had mixed with the white heritage of the European conquistadores, but also with that which was imported from Africa.