Oceanic crust Oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of a tectonic plate. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumulates. The crust overlies the solidified and uppermost layer of the mantle. The crust and the solid mantle layer together constitute oceanic lithosphere. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium. It is thinner than continental crust, or sial, generally less than 10 kilometers thick; however it is denser,
The Layer Monument Layer Quaternity correspond to the alchemical "deities" of Apollo, Luna, Mercurius and Vulcan as named in "Atalanta Fugiens" (1617) by the German alchemist-physician Michael Maier (Emblem XVII). Collectively the Layer Quaternity are a unique alchemical mandala. Through polarized symbolism they delineate essential coordinates associated with Mandala art, namely Space (Heaven and Earth) and Time (Young and Old). Utilizing variety and multiplicity, key attributes of Northern Mannerist art, they also represent fundamental aspects of the human condition, namely, gender, youth and age, pleasure and suffering. A fifth, uniting symbol, a skull, is located at the very centre of the monument. The