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.

The book is a wealth of primary source materials on demographics and the ethnohistory of colonial Mexico.

I have included the two parts with the most numerical data but there are other chapters with excepts from archival documents on the daily life, social mobility, etc. of blacks and other "castas" in Nueva Espana.