travel time. The resulting relationship between the density of the material and the discovered velocity is known as Birch's law. Velocity of compressional waves in rocks The below table shows the velocities for different rocks ranging in pressure from 10 bars to 10,000 bars. It represents the how the change in density, as given in the second column, is related to the velocity of the moving in the material. An increase in the density of the material leads to an increase in the velocity which can be determined using Birch's Law. {| class="wikitable collapsible" |+ Velocities of Compressional Waves in Rocks |- !rowspan=2| Rock Type !rowspan=2| Rock Location !rowspan=2| Rock Density !colspan=4| Wave Velocity (in km/s)at Pressure: |- !10 bar !! 500 bar !! 2000 bar !! 10,000 bar |- | Serpentinite || Thetford,Quebec || 2.601 || 5.6 || — || 5.73 || 6.00 |- | Serpentinite || Ludlow, VT || 2.614 || 4.7 || 6.33 || 6.59 || 6.82 |- | Granite, “G.I.” || Westerly, RI || 2.619 || 4.1 || 5.63 || 5.97 || 6.23 |- | Granite || Quincy, MA || 2.621 || 5.1 || 6.04 || 6.20 || 6.45 |- | Granite || Rockport, MA || 2.624 || 5.0 || 5.96 || 6.29 || 6.51 |- | Granite || Stone Mt., GA || 2.625 || 3.7 || 5.42 || 6.16 || 6.40 |- | Granite || Chelmsford,MA || 2.626 || 4.2 || 5.64 || 6.09 || 6.35 |- | Gneiss || Pelham, MA || 2.643 || 3.4 || 5.67 || 6.06 || 6.31 |- | Quartz monzonite || Porterville,CA || 2.644 || 5.1 || — || 6.07 || 6.37 |- | Quartzite || MT || 2.647 || 5.6 || — || 6.15 || 6.35 |- | Granite || Hyderabad,India || 2.654 || 5.4 || 6.26 || 6.38 || 6.56 |- | Granite || Barre, VT || 2.655 || 5.1 || 5.86 || 6.15 || 6.39 |- | Sandstone || NY || 2.659 || 3.9 || 5.0 || 5.44 || 5.85 |- | Pyrophyllitegranite || SacredHeart, MN || 2.662 || 5.9 || — || 6.28 || 6.45 |- | Granite || Barriefield,Ontario || 2.672 || 5.7 || 6.21 || 6.35 || 6.51 |- | Gneiss || Hell Gate, NY || 2.675 || 5.1 || 6.06 || 6.23 || 6.50 |- | Granite || Hyderabad,India || 2.676 || 5.7 || — || 6.46 || 6.61 |- | “Granite”