556 



IV. NOTICES OF NEW BOOKS. 



I. Geological Observations on the Volcanic Islands visited 

 during the voyage of H.M. S. Beagle, together with some brief 

 notices on the geology of Australia and the Cape of Good 

 Hope ; being the second 'part of the Geology of the Voyage of 

 the Beagle, under the command of Capt. Fitzroy, R. JV., during 

 the years 1832 to 1836. By Charles Darwin, M. A., F.R.S., 

 V.P. G. S., Naturalist to the Expedition. London, pp.176, 

 with a map of the Island of Ascension. 



Almost the whole of this Second Volume of Mr. Darwin's nar- 

 rative is occupied by descriptions of volcanic rocks of various 

 geological ages met with in the island of St. Iago (one of the Cape 

 de Verdes), in Ascension Island, in St. Helena, and in some of the 

 islands in the Galapagos Archipelago. Besides these descriptions, 

 however, the work contains notices of rocks occurring in a few 

 other islands, and some general considerations on trachyte and 

 basalt, and on the distribution of volcanic islands, in addition to 

 notices on Australia and the Cape of Good Hope, alluded to in the 

 title. 



As Mr. Darwin's observations chiefly relate to matters of fact, 

 and are by no means diffusely expressed, it would not be possible 

 in a short notice even to touch upon all the matters discussed and 

 described in this work. It will be more to the purpose to consider 

 the general views of the author with respect to volcanic products 

 and to communicate his views concerning the cause of the upheaval 

 of volcanic craters and islands, and the distribution of these islands 

 on the earth. 



Mr. Darwin observed with regard to the islands of St. Helena, St. 

 Iago, and Mauritius that all three are bounded (at least in the parts 

 he examined) by a ring of basaltic mountains, now much broken, 

 but evidently once continuous (p. 93). The average inclination of 

 these mountains is, however, greater than that which could have 

 been acquired by lava flowing down a sloping surface, and all 

 three islands have been raised in mass. The following ingenious 

 conjecture is offered to explain these circumstances : — "That during 

 the slow elevation of a volcanic district or island in the centre of 

 which one or more orifices continue open, and thus relieve the 

 subterranean forces, the borders are elevated more than the central 

 area, and that the portions thus upraised do not slope gently into 

 the central less elevated area, but are separated from it by curved 



