Please explain last three lines sir.

JUD Classification of Sandstone Several schemes are proposed for classification of sandstones, but the most commonly used schemes include both texture (the presence and amount of either interstitial matrix i.e., clasts with diameters finer than 0.03 millimetre or chemical cement) and mineralogy (the relative amount of quartz and the relative abundance of rock fragments to feldspar grains). Although these classifications were not intended to have tectonic significance, the relative proportions of quartz, feldspar, and fragments are good indicators of the tectonic regime. It is possible to discriminate between stable cratons (rich in quartz and feldspar), orogens (rich in quartz and fragments), and magmatic arcs (rich in feldspar and fragments). tisation of sandstone is shown below in figure. Sandstones are first subdivided into two 450 matrix) consist of a sand-size