The lodes occur in Silurian metamorphic micaceous schists, intruded by granite, porphyry and diorite, and traversed by numerous quartz reefs, some of which are gold-bearing.
All these are wanting in the Pacific area, though there are indications in its gold-bearing gravels that it once possessed them.
The gold-bearing gravels of East Siberia, especially those of the Lena and the Amur, are relatively more prolific than those of West Siberia.
The principal gold-bearing reefs are found along the Witwatersrand (" The Rand ").
The upper valley of the Maranon has undeveloped gold-bearing lodes.
