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.
These are overlaid by sandstones, slates and limestones, alternating with porphyries and porphyrites, sometimes in the form of sheets, sometimes as breccias and conglomerates.
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.
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.
Granites, porphyries and porphyrites belonging to this period occur in the Saxon Erzgebirge, the Harz, Thiiringerwald, Vosges, Brittany, Cornwall and Christiania.