The Rand reefs, first mined in 1886, cover a large area.
They are apparently volcanic. Coral reefs lie off the coasts and render them difficult of access.
The formation is noted for its regularity as regards both the thickness and the gold-tenor of the ore-bearing reefs, in which respect it is unparalleled in the geology of the auriferous formations.
It is surrounded by coral reefs, and is richly wooded.
Round most of the islands there is a luxuriant coral growth; but, as the reefs lie at no great distance, and follow the line of the coast, the inter-island channels are comparatively safe.