4IO 



NATURE 



[March 3, 1892 



marine formations and the different types of deep-sea 

 deposits : their composition, geographical and bathy- 

 metrical distribution. All marine deposits which are not 

 " Littoral," or formed between high- and low-water marks^ 

 or " Shallow-water," a term which the authors limit to the 

 interval between low-water mark and a depth of loo 

 fathoms, are classified in this work as deep-sea deposits. 

 They include Coral Mud, Volcanic Mud, Green Mud, Red 

 Mud, and Blue Mud (which are classed as Terrigenous De- 

 posits, formed in deep and shallow water close to land- 

 masses), and the Pteropod ooze, Globigerina ooze, Diatom 

 ooze, Radiolarian ooze, and Red Clay (which are grouped 

 as Pelagic Deposits, formed in deep water removed from 

 land). In the case of each of these deposits the proportions 

 and characters of the organic and inorganic materials 

 are given, and the results of a large number of chemical 

 analyses, some of which are now published for the first 

 time, are discussed. Perhaps one of the most interesting 

 of the many valuable discussions contained in this 

 chapter is that which deals with the proportions of the 

 ocean-floor covered by different kinds of deposits. A 

 map (Chart I.) is devoted to an attempt to illustrate the 

 nature of the ocean-floor over the whole of the globe, and 

 we cannot resist the temptation of quoting the general 

 estimate to which the authors have been led by their 

 laborious and patient researches. These results are 

 based not only on the collections made during the 

 Challenge}- Expedition, but on many obtained before and 

 since, which have all passed through the hands of the 

 authors ; they include the materials brought up in no 

 less than 1600 soundings from the Atlantic, 300 from the 

 Indian Ocean, and 400 from the Pacific, all from depths 

 exceeding 1000 fathoms. It is evident, therefore, that the 

 map and estimates, though admittedly only approximate, 

 are based on a mass of data such as has never been 

 brought together before. 



The total area of the surface of the globe is estimated 

 at 196,940,700 square miles, of which dry land occupies 

 about 53,681,400 square miles, and the waters of the 

 ocean 143,259,300 square miles. The approximate extent 

 of the areas of the sea-floor occupied by each type of 

 marine deposits is given as follows : — 



Some of the most striking results, which make them- 

 selves apparent from a study of this estimate and the 

 accompanying chart, are the very wide distribution of 

 the Foraminiferal ooze and the red clay in the Atlantic 

 and Pacific respectively ; and the remarkable manner in 

 which the deposits of vegetable origin replace those 

 NO. I166, VOL. 45] 



composed of the remains of animals on the bottom of the 

 Antarctic Ocean. 



Chapter iv., dealing with the materials of organic 

 origin, is, we are informed in the preface, entirely from 

 the pen of Mr. Murray. The Reports of the late Mr. 

 H. B. Brady, of Prof. Haeckel, and of Count Castracane, 

 on the Foraminifera, the Radiolarians, and the Diatom- 

 aceas brought home by the Challenger Expedition, have 

 already supplied naturalists with the means of drawing 

 many important deductions ; but Mr. Murray still finds 

 much to say on the subject, which is not only new, but 

 of very great interest. In the couple of pages devoted 

 to the description of those curious and abundant organ- 

 isms the Coccospheres and Rhabdospheres, which Mr. 

 Murray here refers without doubt to the Calcareous 

 Alga?, we could have wished that he had been able to 

 announce that he had succeeded in inducing some com- 

 petent botanist to undertake the study of the material 

 brought home. One of the most important discussions 

 in this chapter is that on the disappearance of calcic 

 carbonate in the deeper deposits. The estimate made 

 by Mr. Murray of the mean percentage of calcic car- 

 bonate in the different deposits, as the result of a large 

 number of chemical analyses, is as follows : — 



Percentage of CaCOs- 



Coral Mud and Sand 86'4i 



Pteropod ooze 79*26 



Globigerina ooze 64*53 



Diatom ooze ... ... ... 22*96 



Blue Mud and other Terrigenous \ 10-20 



deposits J 



Red Clay 670 



Radiolarian ooze ... 4'oi 



The facts cited by Mr, Murray, on the authority of 

 Mr. John Rathay (p. 282), on the ease with which the 

 remains of the Diatomaceae are dissolved, are of especial 

 importance to the geologist who is called upon to explain 

 the origin of the silica now forming nodules and bands 

 in beds of limestone, and which he is tempted to refer 

 entirely to the larger organisms like Siliceous Sponges, 

 because remains of these are sometimes preserved. All 

 the observations made in the existing deep seas, how- 

 ever, point to the conclusion that the minute Diatoms 

 and Radiolarians play a much more important part in 

 separating the soluble silica from sea-water than do the 

 Siliceous Sponges. 



Chapter v., dealing with the mineral substances found 

 in deep-sea deposits, is full of interest. The mineral 

 particles which are obviously derived from the solid crust 

 of the globe are first dealt with, and in the account of 

 the pumice, the basic volcanic glass, and the palagonite 

 of the deep-sea deposits, Prof. Renard exhibits alike his 

 wide mineralogical knowledge and his skill in dealing 

 with microscopical and often obscure materials. The 

 coloured lithographic plates illustrating this part of the 

 work, which have been drawn by Prof. Renard, and 

 engraved in Vienna, are of wonderful beauty and fidelity. 

 A list of mineral particles detected in deep-sea deposits 

 is given, and includes all, or nearly all, the common rock- 

 forming minerals ; but it is admitted that, with respect to 

 the very minute particles in the finest washings, a con- 

 siderable margin of doubt must always exist regarding 

 their identification. We could wish that it were possible, 

 in the space at our command, to give a summary of the 



