Some of the "porphyroids" which have grains of quartz and felspar in a finely schistose micaceous matrix are intermediate between porphyries and micaschists of this group. Still more numerous are orthoschists of hornblendic character (hornblende-schists) consisting of green hornblende with often felspar, quartz and sphene (also rutile, garnet, epidote or zoisite, biotite and iron oxides).
In this industry, as in the manufacture of cotton goods, Massachusetts has long been without serious rivalry; Brockton, Lynn, The Green Schists and Associated Granites and Porphyries of Rhode Island, Bulletin, U.S. Geological Survey, No.
It is formed chiefly of slates, grits and porphyries of the Cambrian and Silurian systems. It consists of five "ribs" converging at the summit, 3560 ft.
Granites, porphyries and porphyrites belonging to this period occur in the Saxon Erzgebirge, the Harz, Thiiringerwald, Vosges, Brittany, Cornwall and Christiania.
The southern parts of the central range are composed of granites, syenites, porphyries and crystalline slates, while in the north of Ichinskaya volcano, which is the highest summit of the peninsula (16,920 ft.), the mountains consist chiefly of Tertiary sandstones and old volcanic rocks.
The haematites are found not only in the archean porphyries but in Cambrian limestone and sandstone, and in the sub-Carboniferous formations; while the limonites are confined almost exclusively to the Cambrian.
These are overlaid by sandstones, slates and limestones, alternating with porphyries and porphyrites, sometimes in the form of sheets, sometimes as breccias and conglomerates.
Like the highlands of eastern Asia, those of Turkestan are mostly built up on Pre-Cambrian gneisses and metamorphic slates, resting upon granites, syenites, old orthoclase porphyries, and the like.