👉 Subcrustaceous is a geological term used to describe igneous rocks that are composed of a layer of sandstone and siltstone overlaid by a layer of granite or other sedimentary rock. These rocks are typically older than 10 million years, with the oldest being younger than 2-3 million years. Subcrustal is a geological term used to describe igneous rocks that have been formed in the Earth's crust and are composed of a single layer of rock. Examples
