Reviews — Olwers Geology of St. Jlelena. 83 



which gives a masterly, though avowedly imperfect, account of its 

 interesting, but obscure and com})licated, structure. Many points of 

 agreement must of course occur in two careful descriptions of a 

 limited area ; but as Capt. Oliver's stay lately on the island was 

 longer than the Surveying Voyage of the " Beagle" allowed to Mr. 

 Darwin thirty years ago, we may look for, and do find, various 

 points on which some information is added by the artillery officer, 

 who applied his geological knowledge to elucidate some of the 

 structural difficulties of St. Helena, and to enhance the pleasures of 

 his many excursions over and around the island. 



St, Helena is geologically and geographically divisible into three 

 imequal portions, namely, 1st. The south-western district, or " Sandy 

 Bay basin," defined by the remains of the encircling boundary cliffs 

 of an enormous crater, breached at Sandy Bay, and comprising 

 irregular augitic lavas, traversed by great (north-east-south-west) 

 dykes ; 2ndly. The north-western or " Jamestown district" (from 

 Flagstaff Bay to Manati Bay), consisting of uniformly stratified 

 basaltic lavas and clay beds, dipping north-west, and traversed with 

 dykes ; Srdly. The eastern third of the island, or the " Longwood 

 district," composed of more recent volcanic materials, namely, hard 

 lavas, difi'erent from those of the other side of the island, dipping at a 

 low angle to the north-east, and intercalated with whitish clay-stone, 

 with veins of manganese, etc. These nearly horizontal lavas lie on. 

 older, hard, lava beds, upturned, confused, and traversed with many 

 dykes. This latter series seems to comprise disturbed portions of 

 the Jamestown series, and constitutes, with it, the "much broken 

 ring, or rather horse-shoe of basalt," described by Darwin. Some 

 of it, older than the rest, constitutes Darwin's " Basal series" (be- 

 tween the Flagstaff Hill and the Barn, for instance, at the north- 

 east portion of the island). 



The chief points on which Capt. Oliver gives us new information 

 are as follow : — 1. Mr. Darwin was not aware that the base only ©f 

 the remarkable peak called " Great Stone Top" belongs to the 

 " Basaltic Eing series ;" the upper part, of almost 1000 feet vertical 

 height, being a nearly homogeneous cone of grey felspathic rock 

 (phonolite), similar to " Little Stone Top." The latter cone is 

 based on a white claystone, and the two must have originally be- 

 longed to one continuous mass. 2, It is only the summit of " Flag- 

 staff Hill " that is formed of felspathic lava ; the rest is basaltic. 

 The "Basaltic Eing" extends unbroken from "Flagstaff Hill" to 

 " Man-and-Horse," forming the north-west coast. It slopes rapidly 

 upwards towards the central ridge, and is everywhere (high up) 

 overlain conformably by newer felspathic beds. The dip of its 

 strata is much the same throughout, and the great dykes in the fioor 

 of the crater (Sandy Bay basin) run nearly parallel to their strike. 

 The heights of its summits are very uniform, and, except at " Flag- 

 staff," it contains few dykes. The author thinks that the " Flagstaff" 

 has been upheaved by local disturbances, but not so greatly as Mr. 

 Darwin suggests. 3. He strongly doubts the propriety of referring 

 the " Bam" to the " Basaltic Eing." In their aspects and characters 



