^{page 641 note *} See papers by Prof. Tait (May 16, 1881, Proc. Roy. Soc. Edin., vol. xi. p. 217), and by Profs. Marshall and Smith and Mr. Omond (read before Roy. Soc. Edin., July 3, 1882), on the effect of pressure on the maximum density point of water.

^{page 649 note *} On the recommendation of the President and Council of the Royal Society of London, and the Hydrographer, the Lords Commissioners of the Admiralty have detached H.M. surveying vessel “Triton” for two months during this summer (1882), to complete the work commenced in the “Knight Errant,“

^{page 656 note *} In a letter Mr. E. Grove gives me the following additional diatoms from the “Knight Errant” surface gatherings in the Faroe Channel:—

^{page 662 note *} The description of these deposits has been made upon the plan which we have adopted in our work in preparation upon the oceanic deposits, to form one of the reports on the scientific results of the “Challenger” expedition. This is not the place to develop the reasons which have guided us in adopting this mode of description, or to expose, in detail, the methods which we have systematically employed for all the sediments which we are engaged in describing. These will be given in great detail in the introduction to our “Challenger” report. We limit ourselves here, in order to facilitate the comprehension of our descriptions, to describe the order of our tables, and to explain the meanings and arrangement of terms and abbreviations.

The description commences by indicating the kind of deposit (red clay, grey mud, globigerina ooze, &c.), and comprises the microscopic determination of the characters of the deposit, when wet or dry. When we have not given a complete analysis of the deposit, we have always determined the amount of CARBONATE OF CALCIUM. This determination was generally made in estimating the carbonic acid. We took usually, for this purpose, a gram of the substance, and calculated in this manner the carbonate of calcium. Weak and cold hydrochloric acid was used. However, as, independent of the carbonate of calcium, the deposits often contain carbonates of magnesia and iron, the results calculated in placing the carbonic acid to CaO are not perfectly exact. These carbonates of magnesia and iron are almost always in very small proportion, and the result of the process gives that degree of accuracy which we think necessary. The number which follows the words “carbonate of calcium” indicates the percentage of CaCO3; we then give the general designations of the principal calcareous organisms forming the carbonate of lime in the deposit. The part insoluble in the acid, after the determination of the carbonic acid, is designated in our descriptions by the name RESIDUE. The number which follows this word indicates its percentage in the deposits; then follow the colour and principal physical properties. This residue is washed and submitted to regular decantations, which permit the several elements of this insoluble portion being separated according to their density. We divide these portions into three groups—(1) Minerals, (2) Siliceous Organisms, (3) Fine Washings.

1. Minerals.—The number within brackets indicates the percentage of particular minerals and fragments of rocks. This number is the result of an approximate valuation, of which we will give the basis in our report. As it is important to determine the dimensions of the grains of minerals which constitute the deposit, we give, following the contraction m. di., their mean diameter in millimetres. This evaluation is made with the micrometer. We give next the form of the grains, if they are rounded, &c., then follows the enumeration of the species of minerals and rocks. In this enumeration we have placed the minerals in the order of the importance of the rôle which they play in the deposit. The specific determinations have been made.with the microscope, and with the aid of Nicol's prisms, by parallel or convergent light.

2. Siliceous Organisms.—The number between brackets indicates the percentage of siliceous organic remains. We obtain it in the same manner as that placed after the word Minerals. The siliceous organisms and their fragments are examined with the microscope. We have also placed under this heading the glauconitic casts of the foraminifera and other calcareous organisms.

3. Fine Washings.—We designate under this name the particles which, resting in suspension, pass with the first decantation. They are about 0·05 mm. or less in diameter. We have not been able to arrange this microscopic matter under the category of Minerals, because at this small size it is impossible to determine the species. We have always found that the Fine Washings is in considerable quantity as the deposit passes to a clay, and it is from this point of view that the subdivision has its raison d'êtrc. We often designate the lightest particles by the name argillaceous matter, but usually there are associated with this very small fragments of indeterminable minerals, and fragments of siliceous organisms. The number within brackets which follows the words Fine Washings is obtained in the same manner as the similar numbers referred to in the two preceding paragraphs.

These few words will suffice to render our descriptions intelligible. Greater details will be given, as already stated, in our larger work. We may add that in the majority of cases we have solidified the sediments and formed them into thin slides for microscopic examination, and that at all times the examination by transmitted light has been carried on at the same time as the examination by reflected light. Each description is followed by notes upon the dredging or sounding, upon the animals collected, and a discussion of the analysis whenever a complete analysis has been made.

^{page 667 note *} We will not seek here to justify in detail the employment of the terms ancient and recent rocks, but limit ourselves to indicating the meaning which we give to these terms, and the reasons which have guided us in introducing into our descriptions this subdivision of massive crystalline rocks into two groups. This is not the place to enter into the discussion, which is being carried on at the present time among a certain number of lithologists, as to whether the same denomination ought to be applied to the same lithologic type without respect to its geological position.

Whatever may be the issue of these discussions, it remains, nevertheless, true, that there exist certain minute details of structure, and certain characters in the constituent minerals of rocks, differences, in short, sufficiently important to indicate generally if a massive crystalline rock belongs to antetertiary or tertiary and post-tertiary periods. If, as we think, these two groups can be practically distinguished, even although they present insensible transitions from one to the other, then it is important, for an exact knowledge of the origin of sediments, to take this division into consideration in our descriptions of marine deposits. These sediments we know include at the same time rocks and free minerals produced by the disintegration of these rocks. If we are able to apply the distinction into ancient and recent rocks, then we ought, in a certain sense, to be able to tell whether the isolated minerals found in the deposit come from the one or the other type of rock. We should be able, by the aid of this distinction, to determine with probability whether the mineral fragments found in deposits come from continents, are the result of submarine eruptions, or have been carried by floating ice,&c.

Notwithstanding the care which has been taken to establish these distinctions, we are often unable to pronounce with certainty; for, as we have said, the distinctive characters which we have alluded to are not so well marked, the fragments which are present in the deposits are very minute, and many of the finer details have been removed by decomposition. As to the minerals, with which we have more frequently to deal than with the rocks them selves, the difficulty is still greater, on account of their isolated condition and the physico-chemical actions which they have undergone. However, we are often aided by their association with fragments of rock, whose classification is possible; by their being sometimes seen, on microscopic examination, to be bordered by remains of the rock of which they were formerly an integral part; and by their geographical position (which point is also applicable to the determination of the age of fragments of rocks). Whatever we may think of the causes of the characteristic differences of these two lithologic groups, this distinction offers, none the less, a very practical advantage, and if it is applied with care, it throws some light on the interpretation of the facts with which we have to deal.

We cannot dwell, in this note, upon the diagnostic characters which we have employed; we will return to that in the introduction to our Report on the deposits collected during the “Challenger” expedition. As we have had, especially, to study very minute fragments of rocks and of isolated minerals, questions relative to the structure of rocks, properly so called, have been considered only in a subsidiary manner. We give some of the characters which have guided us in the classification into the two groups. We repeat that these peculiarities have only a relative value, and we do not regard them as absolutely conclusive in every case.

We may add that it is especially on the microscopic examination that we have relied for our determinations.

Column I. presents the characters of the principal minerals of ancient rocks —ante-tertiary, the second (II.) those of recent rocks—tertiary and post-tertiary. We only mention those minerals which are found in the deposits.

It is scarcely necessary to mention that all the foregoing refers only to massive crystalline rocks, and when the minerals are in an isolated state we cannot always say whether they come directly from these rocks, or from the disintegration of sedimentary layers, or from schisto-crystalline rocks. These latter frequently occur in the deposits. In these questions we have always taken into consideration the lithological associations and the geographical position of the deposit.

^{page 671 note *} This species is described in Haeckel's “System der Medusen,” p. 640.

^{page 677 note *} See Ann. and Mag. Nat Hist., 1867, vol. xx. p. 287.

^{page 677 note *} Ibid., 1874, xiii. p. 138.

^{page 679 note *} This specimen was 2 feet in length (caudal filament included). When taken from the trawl the pectoral and dorsal fins were covered with a green sheen on a velvety black ground, the sheen being more pronounced at the base of the fins than towards the tips. The back, tail, and head were light brown. The belly and long whip-like portion of the tail were white. There was a bluish colour about the mouth and gills. The eye had a beautiful golden appearance. A green sheen surrounded the pupil.

^{page 689 note *} “Prodromus descriptionis Crustaceorum et Pycnogonidarum, quæ in expeditione Norvegica, anno 1876, observavit G. o. Sars,” Archiv. for Mathematik og NaturvidensJcab, 1876, p. 357.

^{page 690 note *} A description of this species, with the necessary figures, will be given in my report on the Cirripedia of the Expedition of H.M.S. “Challenger.”

^{page 695 note *} As far as our present knowledge goes, no Elasipoda are found living at depths less than 40 fathoms.

^{page 701 note *} The date of the first publication of Düben and Koren's name was incorrectly cited by Dujardin and Hupé (Hist. Nat. Zooph. Éckinodermes, p. 420) as 1834, —a mistake which has subsequently been copied, and has led to an erroneous priority being accorded to Düben and Koren's name. In 1846 Düben and Koren themselves acknowledged Müller and Troschel's claim.

^{page 701 note †} System der Asteriden, 1842, p. 129.

^{page 701 note ‡} Oversigt af Norges Echinodermer, p. 30.

^{page 701 note §} Nyt Mag. f. Naturvidensk., 1877, bd. xxiii. 3, p. 66.

^{page 701 note ║} Kongl. Vet.-Akad. Handl. för År 1844 (1846), p. 250.

^{page 701 note ¶} Loc. cit., p. 251.

^{page 701 note **} Loc. cit., p. 31.

^{page 703 note *} Bull. Mus. Comp. Zool., Harvard, vol ix. no. 1, p. 17.

^{page 705 note *} Nyt Mag.f. Naturvidensk., 1877, bd. xxiii. 3, p. 57.

^{page 706 note *} Duncan, and Sladen, , A Memoir on the Echinodermata of the Arctic Sea to the West of Greenland, London, 1881, p. 39.Google Scholar

^{page 719 note *} This number is very high; possibly it may be infected with an unobserved error. Unfortunately there was not enough of material to repeat either the boiling out or the analysis of the gas resulting from the one boiling.