'The Dorschke’s of Upper Silesia: A Genealogy of the Dorschke’s, Drozdzok’s, Mandrisch’s, Buron’s, Zemelka's, Niestroy’s, Kokot's, Kordula's, Niewrzoll's, Swienty's, etc., with some families tracing to the 1700’s.' Published in Durango, Mexico.
Brian Paul Kaess (Tue,) studied this question.