140 



NATURE 



{Feb. 15, 1877 



been driven through them. No proof of any such move- 

 ment or of any volcanic action older in date than the 

 Eocene, or Upper Cretaceous rocks, was obtained in this 

 Expedition. So that we have here, apparently, an area 

 where any subterranean movements which occurred never 

 disturbed the conformable succession of deposits during 

 that vast section of geological time from the Carbo- 

 niferous (or even from the Silurian) up to the Eocene 

 period. Whether the traces of terrestrial surfaces indi- 

 cated by the plants and lignite beds of the Lower Creta- 

 ceous series, occurring as they do with marine strata 

 below and above them, are to be regarded as marking 

 oscillations of the crust, or as due merely to the gradual 

 up-filling of the old sea-basin and its conversion into 

 lagoons and terrestrial surfaces which were subsequently 

 gently submerged again beneath the Middle and Upper 

 Cretaceous seas, may be a question for discussion. It 

 would seem that coincident with or subsequent to the 

 pre-Miocene'plication and upheaval, volcanic action began 

 in the Western States. Dr. Newberry gives a drawing 

 and a description of a singular basaltic rock called the 

 Needles (Fig. i) rising to a height of 1,700 feet above 

 the Cretaceous floor of one of the tributary valleys of the 

 San Juan, and regards this mass as having been intruded 

 among the strata and as now left visible owing to its 

 superior hardness, while the sui rounding and overlying 

 softer rocks have been washed away. But in his former 

 Report in conjunction with Lieut. Ives, he showed the 

 existence of a group of large extinct volcanoes in the San 

 Francisco mountain group in Arizona, lying on the south 

 side of the Colorado basin. The lava-streams are yet so 

 fresh there that he supposes that the last eruption can hardly 

 have taken place more than a comparatively few years 

 ago. Considerably further to the east in New Mexico, San 

 Mateo rises as another important extinct volcanic cone 

 1 1,000 or 12,000 feet high, whose most recent lavas are so 

 fresh that " it is difficult to believe that they have been 

 exposed to the action of the atmosphere even for so much 

 as a hundred years." Dr. Newberry remarks that similar 

 but smaller volcanic vents equally recent in appearance, 

 but equally inactive now, are scattered over the entire 

 area of the central tablelands from Mexico far up into 

 the British possessions. 



The author, who is an accomplished palaeontologist 

 as well as an active and gifted geologist, has added 

 a valuable Appendix, in which he gives descriptions of 

 the Carboniferous and Triassic fossils obtained by him in 

 the course of the Expedition, and to which Mr. F. B. 

 Meek' contributes an account of the Cretaceous fossils 

 collected. It should be added, that besides the litho- 

 graphic sketches the Report is enriched by some excellent 

 plates of fossils. Archibald Geikie 



DEEP SEA MUDS'" 

 IL 



Peroxide of Manganese. 



"DEROXIDE of manganese occurs widely in ocean deposits, 

 either as nodules, incrustations, or as depositions on the 

 bottom itself. It has been found most frequently in the nodular 

 form in the deep sea clays far from land. It dso occurs in the 

 organic oozes, when these contain much volcanic dibris, or are 

 near volcanic centres. 



In shallow water, near some volcanic islands, it covers shells 

 and pieces of coral or pumice with a light brown incrustation. 



> Since this article was written, the announcement of Mr- Meek's death has 

 reached this country. A more disastrous blow could not have been inflicted 

 upon the progress of palaeontology in the United States. It is much to be 

 desired that amid the unive-sal regret with which the death of this able 

 pateonto'ogist is received, some record shall be published of the services he 

 if^ 'i?"*' ^''^ numerous papers are scattered through so many publications 

 (for he seems to have been ever at the call of any one who needed his 

 assistance), that probably a comparatively small number even of palaeontolo- 

 gists are aware of them all. 



• *r-'k^" '^*^ Distribution of Volcanic Debris over the Floor of the Ocean ; 

 m Character, Source, and some of the Products of its Disintegration and 

 JUecomposition," by Mr. John Murray. Read at the Royal Society, Edin- 

 burgh. Continued from p. 321. 



It has been met with very sparingly, if at all, in shore deposits 

 removed from volcanic centres. 



In my preliminary report above referred to, I stated that 

 further investigation might show that manganese nodules and 

 depositions abound in these regions where we have much of the 

 debris of augitic or heavy lavas. 



A re examination of specimens since our return confirms this 

 view. Wherever we have pumice containing much magnetite, 

 olivine, augite, or hornblende, and these apparently undergoing 

 decomposition and alteration, or where we have evidence of 

 great showers of volcanic ash, there we find the manganese in 

 greatest abundance. This correspondence between the distribu- 

 tion of the manganese and volcanic debris appears to me very 

 significant of the origin of the former. I regard the manganese, 

 as we find it, as one of the secondary products arising from the 

 decomposition of volcanic minerals. 



Manganese is as frequent as iron in lavas, being usually asso- 

 ciated with it though in very much smaller amount. In 

 magnetite and in some varieties of augite and hornblende the 

 protoxide of iron is at times partially replaced by that of 

 manganese. 



In the manganese of these minerals and in the carbonic acid 

 and oxygen of ocean waters we have the requisite conditions for 

 the decomposition of the minerals, the solution of the manganese, 

 and its subsequent deposition as a peroxide. 



The carbonic acid converts the silicates of the protoxides ot 

 manganese, and the protoxides of manganese into carbonate of 

 manganese, and thus prepares the way for oxidation by the 

 oxygen of the water. 



It is probable that the action of the carbonic acid is not appa- 

 rent, and that the manganese is at once deposited as a high 

 oxide if not as the peroxide. This theory is essentially the 

 same as that which Bischof gives for manganese ores generally. 

 I have laid a series of these manganese depositions on the table. 

 An inspection of these and their localities will show that in the 

 clays and oozes the depositions are nodular in form. If a 

 section be made of one of these, a number of concentric layers 

 will be observed arranged around a central nucleus — the same 

 as in a urinary calculus. When the peroxide of manganese 

 is removed by strong hydrochloric acid, there remains a clayey 

 skeleton which still more strongly resembles a urinary calculus. 



This skeleton contains crystals of olivine, quartz, augite, mag- 

 netite, or any other materials which were contained in the clay 

 from which the nodule was taken. In the process of its deposi- 

 tion around a nucleus, the peroxide of manganese has inclosed 

 and incorporated in the nodule the clay and crystals and other 

 materials in which the nucleus was imbedded. The clayey 

 skeleton thus varies with the clay or ooze in which it was formed. 

 Those from a fine clay usually adhere well together ; those from 

 a globigerlna ooze have an areolar appearance ; those from a 

 clay with many fine sandy particles usually fall to pieces. Mr. 

 Buchanan informs me that the purest portions of these nodules, 

 that is those portions made up of closely-packed concentric 

 layers, contain from 30 to 34 per cent, of the peroxide. 



Taking the nodule as a whole, it will of course contain very 

 much less than this. The nucleus varies in each nodule, and 

 that part of a nodule which is made up of concentric layers will 

 vary with each locality and with the depth from which it comes. 

 We may expect, therefore, that analysis will show considerable 

 variations in the amount of alumina, silica, and metals, lime, 

 &c., in the nodules from different stations. At some places in 

 the Pacific the nodules show periods of deposition very distinctly. 

 We have first a very compact nodule which may have a shark's 

 tooth for a nucleus, and which appears to have been formed 

 slowly. Then there would seem to have been a shower of ashes. 

 After a time manganese was again deposited, inclosing in the 

 nodule a layer of these ashes. The most frequent nucleus in 

 the nodules is a piece of pumice or other volcanic fragment. 



In deep sea clays, far from land, sharks' teeth, ear-bones of 

 whales, and fragments of other bones are very o'ten the nucleus 

 around which the manganese is deposited. In one instance a 

 piece of siliceous spon^ie forms the nucleus. In a globigerina 

 ooze a portion of the deposit has apparently formed the nucleus. 

 In these we have perfect casts of the foraminifera, but all the 

 carbonate of lime has been removed. The volcanic fragments 

 which have formed the nuclei of nodules appear frequently to 

 have undergone peculiar alterations. For instance, obsidian is 

 usually surrounded by beautiful agate bands. 



When we found the bottom composed almost entirely of vol- 

 canic ashes, or so hard from other reasons that the sounding tube 

 did not penetrate it, the manganese was deposited in layers over 



i 



