Uluru mapping and describing the geological history of the area, geologists refer to the rock strata making up Uluru as the Mutitjulu Arkose, and it is one of many sedimentary formations filling the Amadeus Basin. Uluru is dominantly composed of coarse-grained arkose (a type of sandstone characterized by an abundance of feldspar) and some conglomerate. Average composition is 50% feldspar, 25–35% quartz and up to 25% rock fragments; most feldspar is K-feldspar with only minor plagioclase as subrounded grains and highly altered inclusions within K-feldspar. The grains are typically in diameter, and are angular to subangular; the finer sandstone is well
Local attraction Local attraction While compass surveying, the magnetic needle is sometimes disturbed from its normal position under the influence of external attractive forces. Such a disturbing influence is called as local attraction. The external forces are produced by sources of local attraction which may be current carrying wire (magnetic materials) or metal objects. The term is also used to denote amount of deviation of the needle from its normal position. It mostly causes errors in observations while surveying and thus suitable methods are employed to neglect these errors. The sources of local attraction may be natural or artificial. Natural sources include