什么是 Textural maturity, compositional maturity？

The textural maturity of a sand or sandstone measures how far the sorting, abrasion and winnowing of the current have worked on it, in four stages: immature, with more than $5\,\%$ of clay matrix; submature, with less clay but poorly sorted grains ($\sigma > 0.5\,\varphi$); mature, with little or no clay and well-sorted ($\sigma < 0.5\,\varphi$) but angular grains; supermature, with no clay and grains both well sorted and well rounded. Its compositional maturity measures how far the unstable minerals and rock fragments have been removed, leaving quartz: it is high in a sandstone of nearly pure quartz and low in one rich in feldspar, mica or fragments of rock.