Rootlets are plant trace fossils that mark ancient soil surfaces. They are very useful as way-up indicators and help determine depositional environment and orientation. The presence of organic matter indicates that the past environment was able to sustain life and that precipitation and nutrients were available. Roots spread out in a downward direction, so when examining a sample, the more condensed end is at the surface (up) and the direction they fan out towards is below the surface. The arrow in this image depicts the way up.