Comparison of results obtained from a variety of natural rock samples using both continuous and alternating field ( c .f and a.f) techniques demonstrates the complementary nature and potential of the two techniques . The re mane nee coercivity spectrum is analyzed by obtaining families of hysteresis curves inc .f of up to 1200 mT. The extraction of the decay curves from the composite back-field curves reveals several important features: interacting fields among magnetic carriers occur in all rock types investigated including redbeds; the interaction takes place at the low end of the spectrum and its effect is defined by a new parameter - the crossing point; a co-ordinate (Rep) of this parameter which varies among, but remains essentially constant within, rock types can be used as a classification index. For most specimens, the remanence (NRM) acquired in the earth's field is only a small fraction (J0-3 - 10-4 ) of their saturation re mane nee meaning that the application of the a.f procedure to recover the NRM must be carefully devised. Treatments in a.f up to 290 mT indicate that a.f is much more effective than c.f for unlocking remanences. Thus, a clear distinction has to be made between the remanence coercivity (re) spectrum and the remanence a.f stability (rafs) spectrum. An effectiveness ratio (Re) of the c.f and a.f required to reduce a saturation remanence to a certain level is used to establish a relationship between those two spectra. The Re varies with rock types and thus can be used as an identification index; in many instances, the ratio remains nearly constant within the rock type .- The method of combining detailed c .f and a.f experiments provides an effective means of ascertaining whether or not the re spectrum of a natural rock has been investigated in its entirety, - a prerequisite that needs to be met if the a.f data, so widely used in paleomagnetism, are to be interpreted correctly.