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Despite its importance to the study of continental crustal evolution, the composition of the lower part of the Earth's crust remains poorly known, largely because of the difficulty of directly sampling significant portions of it. Samples of lower-crustal rocks, which can be obtained from either xenoliths or high-grade metamorphic terrains, provide invaluable information on the composition of the deep crust, but it is difficult to assess their applicability to the lower crust as a whole. Geophysical techniques, however, provide a means of indirectly measuring, physical properties across large sections of in situ lower crust. The physical properties determined by geophysical field experiments can then be compared to those measured in the laboratory on lower-crustal rock types, thereby placing constrainl $ on the composition of the deep crust. One such physical property, which can be measured with seismological techniques, is seismic velocity. We can infer the seismic velocity structure of the lower continental crust in two ways: either through seismic experiments on the Earth's surface, in which the velocity of seismic waves propagating through the lower crust is determined, or by measuring the speed of sound in laboratory specimens of rocks believed to have once resided in the lower crust Each of these methods has advantages and drawbacks: seismic reflection/refraction studies provide information on the geometry and velocity structure of the in situ lower crust, but they are relatively expensive, and their resolution is limited by the wavelengths used (0.2-1.0 km). Laboratory studies, on the other hand, allow precise, relatively inexpensive measurements of …