Short-period vertical seismometers are used in deep holes at several sites to obtain the change with depth in amplitude and phase spectra of short-period seismic noise. Although the observed spectra can be explained by an arbitrary combination of several Rayleigh modes, an alternative theory is suggested here. An attempt is made to explain both amplitude and phase spectra of observed microseisms of period less than 6 sec in terms of standing-wave phenomena caused by steady-state plane harmonic compressional waves propagating vertically through a horizontally stratified medium. At most sites, the observed data indicate satisfactory agreement with the expected results. A considerable fraction of the short-period noise may, therefore, be regarded as P-wave noise propagating vertically from below

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