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
Fire-cracked rock Fire-cracked rock In archaeology, fire-cracked rock (FCR) or fire-affected rock (FAR), is rock of any type that has been altered and split as the result of deliberate heating. It is a feature of many archaeological sites, throughout the United States. In many cases, fire-cracked rock results when stones were used to line hearths and earth ovens or were heated to provide a longer-lasting heat-source (similar to a modern hot water bottle). In other cases, fire-cracked rock results from stone being used to heat or boil water; the stones were heated and dropped directly into water held in containers made of