Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.
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By placing the body in a sleeplike state, the Gateway tapes achieve the same goal as meditation in that it places the body in such a profoundly relaxed state that the bifurcation echo slowly fades away as the heart lessens the force and frequency with which it pushes blood into the aorta.