A Spectral Natural Gamma-ray log has been run in a borehole in Ermelunden. The vertical distribution of Th, U, and K is similar to that observed in neighbouring boreholes. A new measuring and data processing technique was used and the probes own background signal was determined. Surprisingly a signal not originating form Th, U, or K was observed. It is concluded that the signal is due to neutrons originating from nuclear interactions between energetic cosmic particles and atoms of the soil. After slowing down to thermal energies the neutrons are captured in hydrogen and 2.2 MeV capture gamma-rays are emitted and detected by the probe. The intensity of cosmic radiation varies with depth, and, therefore, slightly influences the accuracy of the thorium concentration determination.