Over hundreds of million of years the sedimentary rocks may be squeezed, heated, and contorted by huge parts of the EarthΓÇÖs crust pushing against one another as mountain and valley building occurs. This causes the sedimentary rock to change into metamorphic rock and it usually destroys all the fossils in what used to be the sedimentary rock. During metamorphosis, mudstone becomes slate, sandstone becomes quartzite, and limestone becomes marble.
