REPORT ON THE DEEP-SEA DEPOSITS. 
205 
aggregations appears to be greater than that of somewhat similar ones from other stations, 
and may be due to the cementation of the isolated particles by colloid siliceous matter. 
In this specimen there are finally some very peculiar white-coloured aggregations com- 
posed of minute rhombohedral crystals, which when treated with dilute acids decompose 
with liberation of carbonic acid, but a flocculent residue is left behind, as well as micro- 
scopic granules ; we are inclined to consider these crystals as calcite or dolomite. The 
general appearance of this deposit under the microscope is shown on PI. XV. fig. 3, and 
the fine washings are represented on PI. XXVII. fig. 5. 
Professor Haeckel and Dr. Dreyer have recognised in the material from this station 
no fewer than 338 species of Eadiolaria, belonging almost entirely to the two legions : 
Nassellaria and Spumellaria, only two species being noted belonging to the Phmodaria, 
while the Acantharia are quite absent, as is nearly always the case in the deep sea, 
owing to the acanthin skeleton being easily decomposed.^ The Nassellaria are by far the 
most abundant in this deposit, the number of species compared with that of the 
Spumellaria being as 2 to 1 ; about three-fourths of the Nassellaria, and half of the 
total Eadiolaria, belong to the orders Spyroidea and Cyrtoidea. 
A detailed account has been given of this, the deepest sounding, because we consider 
it the most typical Eadiolarian Ooze that has yet been discovered. It is estimated that 
about 80 per cent, of this sample is made up of the remains of siliceous organisms. The 
specimens from lesser depths in the Central Pacific and from the tropical regions of the 
Indian Ocean are less pure. Whenever a Eed Clay is estimated to contain 20 per cent, 
of the skeletons of Eadiolaria and siliceous organisms other than Diatoms, it has been 
classed as a Eadiolarian Ooze. There seems to be little doubt that the Eadiolaria are, 
like the calcareous Foraminifera, slowly dissolved by the sea- water after the death of the 
organisms, for the skeletons and spicules are frequently seen reduced to the merest 
threads, or in some parts the fenestrated spheres of some species are wholly removed.^ 
In the Tables of Chapter II. nine deposits collected by the Challenger Expedition are 
described as Eadiolarian Oozes, and numerous other samples have been subsequently 
procured by other expeditions in the Pacific and Indian Oceans. The above-mentioned 
nine samples range from 2350 fathoms at Station 273 to 4475 fathoms at Station 225, 
^ Haeckel states that “ the skeletons of the Phaeodaria consist of a compound of organic substance and silica,” and 
regards “ acanthin as a substance related to chitin ” (see “ Report on the Radiolaria,” Zool. Chall. Exp., pt. xl. pp. 
Ixix, Ixx); he says further that “ the Acantharia are entirely wanting [in deep-sea deposits], for their acanthin skeleton 
readily dissolves” (l.c., p. civ.). Murray records one species of Acantharia (Pantopelta icosaspis) from the Diatom Ooze, 
Station 157, 1950 fathoms, Southern Indian Ocean (see Scot. Geogr. Mag., vol. v. pp. 433, 4, 1889). 
2 If we take into account the molecular state of the silica forming the skeletons of Radiolarians, it is easily con- 
ceivable that they may pass into solution in the sea-water after the death of the organisms, but this dissolution cannot 
be very rapid, as will be seen from the following experiment. Some of the Eadiolarian skeletons from Station 266 
were treated in a water-bath in a solution of 2 grms. of carbonate of potash, the water being renewed as evaporation went 
on. This operation was continued for thirty hours with the result that of 0'4725 grm. of Eadiolarian skeletons, dried at 
110° C., 0‘0607 grm. of silica passed into solution, equal to 12-84 per cent. Owing to the difficulty of separating the 
Radiolarians from the argillaceous matters, it must be pointed out that we were not dealing with pure Eadiolarian 
skeletons. See also Schulze, “ Report on the Hexactinellida,” Zool. Chall. Exp., pt. liii. pp. 26, 27. 
