The effect of clay and saline solutions on the complex dielectric properties of geologic formations is not theoretically understood, nor are there satisfactory empirical relations for such complex media. In this work, measurements of the dielectric constants are reported for consolidated sandstone cores containing a fixed percentage of clay with varying salinity and water content. In order to study the effect of varying clay content, the dielectric constants of different sand-clay mixtures were also determined. The measurements were carried out at higher frequencies than previously reported, i.e., in the VHF and microwave range (20 MHz to 1 GHz). The effect of clay increases the real part and decreases the imaginary part of the complex dielectric constant compared to the ''clean'' sandstone samples. The pronounced frequency dependence on clay, water content, and salinity disappears at our higher frequencies.