;64 



NATURE 



[Feb. 20, 1890 



made during the voyage of the Challenger. Prof. Tait's 

 paper has indeed little connection with the work of the 

 Expedition. Mr. Buchan and Commander Creak have 

 worked up an immense amount of matter derived from 

 other sources. 



The records of the Challenger have not only added 

 facts of great importance to our stock of knowledge ; 

 but have been, as it were, nuclei round which a host of other 

 observations have crystallized into orderly arrangement. 

 Each one of the authors has made a step forward. Prof. 

 Tait has extended the range of pressure over which com- 

 pressibilities have been measured. Mr. Buchan has 

 attacked the diurnal climatology of the ocean. Com- 

 mander Creak has given a new turn to our ideas on the 

 secular change of terrestrial magnetism. It is only to be 

 regretted that the exclusive use of British systems of 

 measurement, and the other blemishes to which we have 

 felt compelled to refer, give a certain insular appearance 

 and character to a work of world-wide interest. 



The Report on the Rock-Specimens collected on 

 Oceanic Islands, by Prof. A. Renard, consists of 180 

 pages, well illustrated by woodcuts and seven maps, and 

 constitutes a very important part of the petrology of the 

 Challenger Expedition. The account of the rocks of St. 

 Paul's from the pen of Prof. Renard has already appeared 

 in Vol. II. (Narrative), Appendix B, of the Challenger 

 Reports, and we are glad to learn from the preface to 

 the volume now before us that the " Report on Deep- 

 Sea Deposits " which has been so long looked for by 

 geologists, is to be issued next month. 



Mr. Murray is to be congratulated on having secured 

 the services of so able a mineralogist and petrographer 

 as Prof. Renard to describe the rocks brought home by 

 the Expedition. Most of these descriptions have already 

 appeared in the Bulletin of the Mtis'ee Royal (THistoire 

 Naticrelle de Belgique ; but English geologists will be 

 glad to see them collected together and published in their 

 own language, and in a convenient form for reference. 



Prof. Renard explains in his opening remarks the 

 grounds for publishing this account of the rock-specimens 

 collected on the oceanic islands by the officers of the 

 Challenger Expedition : — 



" Mr. Murray had discovered that loose volcanic 

 materials played a very large part in the formation of the 

 deposits of the deep sea, and it was considered desirable 

 to institute a comparison between these and the products 

 of the same origin in volcanic islands situated in or on 

 the borders of the great ocean basins." 



It is at the same time admitted, by the editor of the 

 volume, that Prof. Renard's lithological and mineralogical 

 descriptions must be regarded rather as contributions to 

 the geology of the islands visited, than as supplying full 

 and descriptive discussions of the subject. 



" The necessities of the voyage, bad weather, or the 

 difficulties of the exploration, prevented, in many cases, 

 the naturalists from passing more than an hour or two on 

 shore ; they were thus unable to give any detailed account 

 of the stratigraphical relations, and the collections of 

 hand-specimens were sometimes limited to those rocks 

 situated near the coast." 



In the case of Tenerife, of which we have such full 

 descriptions in the writings of Von Fritsch and Reiss, 

 and of Sauer ; in that of the Cape de Verde Islands, the 



rocks of which have been carefully studied by Dolter ; 

 and of Fernando Noronha, which has been surveyed and 

 its rocks admirably described by Profs. Branner and 

 Williams, it is obvious that the description of the specimens 

 placed in the hands of Prof. Renard can only be regarded 

 as supplementary to the fuller and more comprehensive 

 accounts of the geology of the islands which we already 

 possess. But in the case of some of the smaller islands,. 

 I like Tristan da Cunha, Marion Island, and Heard Island 

 I the notes in the present Report constitute almost the only 

 I materials which exist for judging of their geological con- 

 stitution and structure. In the case of the Island of St. 

 Thomas, in the West Indies ; of Kandavu, in Fiji ; of the 

 volcano of Goonong Api, in the Banda Islands \ of the 

 volcano of Ternate, and of several islands in the Philip- 

 pine Group, Prof. Renard has taken the opportunity 

 afforded to him by the receipt of interesting specimens 

 casually collected, to discuss points of considerable 

 mineralogical and geological interest. 



Quite apart from their connection with certain localities,, 

 these very careful notes of Prof. Renard on peculiarities 

 exhibited by rock-forming minerals are of much value to 

 geologists ; and so also are the series of analyses of these 

 rock-specimens, made, evidently with great care, by Dr. 

 Klement. 



So many of the islands visited by the Challenger were 

 previously touched at by the Beagle, on board of which 

 Charles Darwin was acting as naturalist, that it is im- 

 possible to avoid comparing the work before us with that 

 author's classical memoir, " Geological Observations on 

 the Volcanic Islands," which was published in 1844 and 

 re-issued in 1876. In spite of the improvements of our 

 petrographical methods during the half-century, which 

 has witnessed the application of the microscope to the 

 study of rocks, it is very interesting to see how often 

 observations made by Darwin, aided by that great 

 pioneer in crystal lographic research. Prof. W. H. Miller 

 of Cambridge, are confirmed by the painstaking labours 

 of Prof. Renard. There is, perhaps, some danger, at the 

 present day, that the facilities afforded for the micro- 

 scopic study of rocks, by the aid of transparent sections^ 

 should lead geologists and mineralogists to despise, or 

 to regard as of small value, the observations made with- 

 out such aid. To those who entertain such an idea, it 

 will be instructive to see how Darwin and Miller by the 

 aid of pocket-lens, knife-blade, and magnet, were often 

 able to form an appreciation of the mineralogical constitu- 

 tion of rocks, which has been very largely confirmed by 

 the application of the more refined methods of the 

 present day. 



The discussion of great geological problems, which, as 

 treated by Darwin in 1844, contributed so largely to the 

 interest excited by his book, have of course not come 

 within the scope of the work undertaken by Prof. Renard. 

 The particular varieties of volcanic rocks in Ascension,- 

 which Darwin found to illustrate in so striking a manner 

 the origin of foliation in the crystalline schists, do not 

 seem to have been among those collected by the officers 

 of the Challenger. But as an important contribution to 

 micropetrography, the work of Prof. Renard is of the 

 highest value, as might indeed have been anticipated 

 from the well-proved skill and acumen of the author ia 

 this interesting branch of scientific research. 



