They include gypsum, dolomite, conglomerates, phyllites, and a basic series of eruptive rocks (gabbros, peridotites, serpentines).
The phyllites (q.v.) form a middle term between this group and the slates; they consist usually of quartz, white mica and chlorite, and have much of the foliation and schistosity of the mica-schists.
By advancing crystallization and increased size of their components, slates pass gradually into phyllites, which consist also of quartz, muscovite and chlorite.
Thus, we find them more frequently, folded, tilted and cleaved; the muds have become shales, slates, phyllites or schists, the grey and red sands and conglomerates have become quartzites and greywackes, while the limestones are very generally dolomitized.
The oldest, or Keis, series consists of quartzites, quartz-schists, phyllites and conglomerates.