Dec. I, 1887] 



NA TURE 



99 



life. But in spite of the frequent changes of scene which 

 they enjoy, or endure, and their unique opportunities for 

 pursuing scientific researches, and in spite of their early 

 acquaintance with elementary treatises on several branches 

 of science, it is only at rare intervals that naval surgeons 

 appear as observers or investigators. The unusual 

 occasionally happens, and in the work by Mr. Guppy on 

 the Solomon Islands we have an admirable example of 

 what may be accomplished by an energetic observer alive 

 to his advantages. 



In this volume it would not be difficult to point out many 

 imperfect forms of expression, some a,voidable confusion 

 in arrangement, even a few conclusions that the facts 

 hardly appear to warrant ; but these sink into insignific- 

 ance when compared with the mass of valuable material 

 from which they might be culled. 



The object of the book is to describe fully, but in a 

 general way, the author's geological observations on the 

 islands of the Solomon Group, little space being devoted 

 to the other subjects mentioned in the title. It is a com- 

 pendium of important facts, most of them new to the 

 scientific public. Perhaps the Journal of the Geological 

 Society is hardly suited for recording a series of laborious 

 and detailed observations on the rocks of a remote archi- 

 pelago, and the publications of the Royal Society of 

 Edinburgh — where detailed papers by Mr. Guppy appear 

 — may not be read by all geologists. It may not be in- 

 appropriate, in these circumstances, to mention a few of 

 the facts observed by Mr. Guppy and recorded in this 

 volume. 



The book is divided equally between the description of 

 volcanic and calcareous islands, and is illustrated by mips 

 and sections. 



The volcanic rocks collected on the islands were sub- 

 mitted for mineralogical analysis to Prof. Judd and Mr. 

 T. Davies ; the calcareous formations were studied by Mr. 

 John Murray : and the remains of animal life, both fora- 

 miniferal and coral, are being examined by the leading 

 specialists ; hence the work is enriched by the labours of 

 well-known men, and the " gold" of the author's data im- 

 pressed with the " guinea-stamp" of recognized authority. 

 The volcanic islands of the group are divided into two 

 classes. First, those of comparatively modern forma- 

 tion, composed mainly of little-altered augite-andesites, 

 andesiticpitchstones, tuffs, and agglomerates : these islands 

 still preserve the volcanic outline and sometimes give evi- 

 dence of recent activity by terminating in craters with hot 

 springs or fumaroles. The second class is composed only 

 in part of these rocks, and in part of much more ancient 

 crystalline masses consisting chiefly of altered dolerites, 

 quartz-diorites and -porphyries, and serpentines. Some 

 islands of the latter class exhibit an extraordinary 

 diversity in petrological character. Fauno, the de- 

 scription of which is illustrated by a geological map, is an 

 interesting instance of this. The northern end of the 

 island is occupied by a precipitous mountain of andesitic 

 tuff sloping steeply down from an altitude of 1900 feet to 

 a narrow isthmus, 150 feet high, composed of horn- 

 blende-augite-andesite, and leading to a sickle-shaped 

 peninsula of successive hills connected by lovv strips 

 of rock. The composition of this crescentic tongue 

 is successively altered dolorites, quartz-porphyries, quartz- 

 andesites, hornblende-andesites, and altered dolerites 



again. These rocks, almost invariably massive and 

 unassociated with tuffs or agglomerates, each in turn oc- 

 cupy the whole breadth of the peninsula. The mode 

 of formation which Mr. Guppy demonstrates for this 

 promontory is illustrated in various stages by several 

 other islands. A series of small volcanoes arising in a 

 crescentic form, and each pouring out a characteristic lava, 

 were gradually elevated and so brought into connection. 

 Rapid denudation, caused by the great rainfall of the 

 region, wore off the volcanic contours and reduced the 

 chain of peaks to a series of" necks" in close juxtaposi- 

 tion. The comparative rarity of fragmental volcanic rocks, 

 and the mineralogical constitution of the massive crystal- 

 line lavas of the surface, indicating their solidification at 

 great depths, prove extensive denudation to have taken 

 place all over those islands. 



The main interest of the book centres in the researches 

 of Mr. Guppy on calcareous deposits. He is the only 

 geologist who has visited this most instructive group of 

 coral islands ; and he describes what he saw there with a 

 straightforward simplicity that compels confidence in the 

 accuracy of his observations, and affords to those who 

 may find his theory insufficient all possible data for 

 disproving it. 



Mr. Guppy gives the following classification of the 

 limestones of a "coral island" in the Solomon Group as 

 revealed to him by the walls of the river gorges he 

 explored : — 



Group I. — Coral Limestones, properly so called. 



Group II. — Coral Limestones which have the compo- 

 sition of coral muds or sands now forming near coral 

 reefs. There are three subdivisions of this group : (i) 

 crystalline limestone, in which coral plays a secondary 

 part, and remains of calcareous Alg£E and mollusks pre- 

 dominate ; (2) chalky limestones ; (3) homogeneous 

 fawn-coloured limestones, often crystalline. 



Group III. — Rocks of the composition of volcanic mud 

 and pterojiod 002e, conta-ining also numerous Foraminifera, 

 These are subdivided into (i) partially consolidated vol- 

 canic muds ; (2) partially consolidated pteropod ooze ; (3) 

 hard limestones. 



Group IV. — Foraminiferal Limestones, or consolidated 

 " Globigerinaooze." There are two classes : (i) composed 

 chiefly of tests of both pelagic and bottom-living Fora- 

 minifera : (2) chiefly composed of the tests of pelagic 

 Foraminifera. 



Group V. — Rock resembling a consolidated deep-sea clay 

 (Red Clay). 



The two last-named groups were certainly deposited at 

 depths not much less than 2000 fathoms in an ocean far 

 from continental land, and their existence above sea-level 

 is now for the first time proved. 



From all the facts that could be ascertained regarding 

 the coral formations of the group, certain inferences were 

 drawn, which we give in the author's own words : — 



" The first is self-evident, viz. that these upraised reef 

 masses, whether atoll, barrier reef, or fringing reef, were 

 formed in a region of elei'ation. . . . It is apparent that 

 Mr. Darwin's theory of coral reefs, which ascribes atoll 

 and barrier reefs to a movement of subsidence, cannot be 

 applied to the islands of the Solomon Group. . . . 



" The second inference is, that such upraised reefs are 

 of moderate thickness, their vertical measurement not ex- 

 ceeding the usual limit of the depth of tlie reef -coral zone. 



