Rock (geology) arkoses (12%). Sedimentary rocks often contain fossils. Sedimentary rocks form under the influence of gravity and typically are deposited in horizontal or near horizontal layers or strata and may be referred to as stratified rocks. A small fraction of sedimentary rocks deposited on steep slopes will show cross bedding where one layer stops abruptly along an interface where another layer eroded the first as it was laid atop the first. Metamorphic rocks are formed by subjecting any rock type—sedimentary rock, igneous rock or another older metamorphic rock—to different temperature and pressure conditions than those in which the original rock was
2012 North American heat wave the west, causing the core of the hot weather to the build in the Mountain States and the southwest U.S. shifting eastwards again by mid-July. By early August, the core of the heat remained over the Southern Plains. The heat wave formed when high pressure aloft over the Baja of Mexico strengthened and moved over the southern plains around June 20–23 and then spread east and northward, remaining fixed over the center of North America through July 2012. The direct cause of the heat is that, under high pressure, the air subsides (sinks) toward the surface. This sinking air acts