While serving in Austria, Berezin diligently collected materials on ethnography and statistics of local Slavs; the fruit of these occupations was the book "Croatia, Slavonia and Dalmatia," published in St. Petersburg in 2 volumes, in 1879. This work, which delivered the author of the order from the Austrian, Italian, Serbian and Montenegrin governments, is based mainly on printed sources published in Austria, but the ethnographic part contains a lot of material learned by Berezin from the direct observation of popular life.