Heiligkreuzgebirge
While at the University of Warsaw, she started her master's research. This allowed her to join expeditions with other paleontologists and make various contributions. Kielan-Jaworowska participated in her first paleontological excavation in 1947 along with a group of researchers from the Museum of Earth and the National Geological Institute. The excavations, led by the geologist Jan Czarnocki, took place in Poland's Świętokrzyskie Mountains in exposures of Middle Devonian strata. The group's work involved digging for soft rock and rinsing away the sediment, consisting of yellow marl, in running water while using a sieve to collect any fossils that were present. Kielan-Jaworowska spent two months with the group and specifically sought trilobite fossils, which became the focus of her master's thesis. She returned to specific sites in the Świętokrzyskie Mountains over the next three summers to continue developing her collection, which grew to over one hundred trilobite specimens.