Noun. 1. prefrontal cortex-the anterior part of the frontal lobe. prefrontal lobe. cerebral cortex, cerebral mantle, cortex, pallium-the layer of unmyelinated neurons (the grey matter) forming the cortex of the cerebrum. lobe - (anatomy) a somewhat rounded subdivision of a bodily organ or part; ear lobe.refrontal lobe. cerebral cortex, cerebral mantle, cortex, pallium-the layer of unmyelinated neurons (the grey matter) forming the cortex of the cerebrum. lobe - (anatomy) a somewhat rounded subdivision of a bodily organ or part; ear lobe.
1. igneous rocks: formed by the cooling and hardening of magma (molten rock) from inside Earth. 2. sedimentary rocks: formed by the compaction and cementing of layers of sediment (rock fragments, plant and animal remains, minerals from water) 3. metamorphic rocks: formed by the effect of heat and pressure on other rocks. *Earthâs crust is made-up primarily of igneous rocks.
An introduction to SEDIMENTARY ROCKS Sedimentary rocks form from sediment. Sediment is a general term that indicates loose grains (such as the sand at the beach) and chemical precipitates (such as crystals of salt). Sedimentary rocks can be subdivided in three categories: clastic, chemical, and biochemical sedimentary rocks. a. clastic (or detrital) sedimentary rocks Clastic sedimentary rocks form when individual grains (the sediment), made by fragments of rocks, minerals, or shells, are cemented together (the clastic sediemntary rock).