Geological map - Geological map of Saint Helena - http://geowww.ou.edu/~bweaver/Ascension/shgeolmp.htm
Natural History - Geology - St. Helena is a volcanic island although volcanic activity has long since ceased. The last volcanic eruptions occurred about 7 million years ago and since that time the island has been sculpted into its present form by the forces of erosion. - http://geowww.ou.edu/~bweaver/Ascension/sh-nat.htm
St Helena - Physical Geography - The Geology of the island of St Helena, South Atlantic Ocean - http://www.btinternet.com/~sa_sa/st_helena/st_helena_geology.html