The dataset contains condensed results of seismic refraction survey, that can be regarded as “hard data”. Data files Syczyn-1_P.ASC and Syczyn-1_S.ASC represents tables obtained for line Syczyn-1, wave P and wave S respectively; Data files Syczyn-2_P.ASC and Syczyn-2_S.ASC represents tables obtained for line Syczyn-1, wave P and wave S respectively. Each file contains 4 columns: Record No. – sequential record identifier; Source location – distance from the beginning of the line to the (current) source point (in meters); Receiver location – distance from the beginning of the line to the given receiver (in meters); First Break – delay time between emission of the wave to its arrival at the given receiver point (seconds). Dataset is formatted in simple table, that can be imported to other seismic software for modelling velocity field. Different computing algorithms generate slightly different velocity models, so it can be useful to have hard data for comparison.