Pfefforkorn's book is a valuable document for several reasons: it records evsery aspect of Sonora (now extrene northwest Mexico and southern Arizona)as it was in the 18th century. Pfefferkorn describes its native tribes, its geology, geography, biology, botany, entomology and more, at a time when those sciences had not yet been named. He gives an insight into the life and purposes of Christian missions in what was then New Spain. The prefaces by Theofore E. Treutlein (translator) and by Bernard L. Fontana give a notion of Pfefferkorn's biography, including the tragic circumstances of the expulsion of the Jesuits from Spain and allheer colonies. A great research tool.