THE DEPOSITS OF THE SEA-BOTTOM. 8l 



parations. The Diatoms, on the contrary, are chiefly found in the finest specimens, under o-oa"" 11 , and 

 only a few larger forms are met with among the particles 0-05 o-02 mm . With regard to the forms of 

 these organisms, I, of course, cannot have much to say, as I do not know the individual genera and 

 species. All the siliceous organisms are single-refracting, and consist of hydrous silica; a few Radio- 

 laria may however be found with spheroid double-refraction, and consist accordingly of quartz or 

 chalcedony. The Sponge spicules appear generally as quite smooth, straight bodies with almost pa- 

 rallel sides, and generally with a hollow in the middle; the refraction is for these organisms, as also 

 for the other siliceous organisms, somewhat slighter than that of the Canada balsam, and thus they 

 are rather conspicuous in the balsam. The larger Sponge spicules are often regularly ramified, com- 

 monly with three branches from each point of division; sometimes they take the form of an anchor 

 or of other regular figures. The Sponge spicules are more rarely granulated on the surface, and it 

 is still more rare to find them of a sinuous form. The Radiolaria are generally globular with a very 

 different size of meshes and equipment of radiating rays; in a few specimens other forms are found 

 in larger quantity, partly south and southwest of Iceland, partly between Iceland and Greenland. Far 

 the greater part of the Diatoms are circular, belonging to the genus Coscinodiscus or nearly allied 

 forms; different oblong forms and attached Diatoms are however found here and there in all the 

 specimens; other types are far more rarely met with. 



The siliceous organisms have been found in all the specimens only excepting two; and in these 

 two specimens they might perhaps also be found by a closer examination. The Sponge spicules are 

 most widely distributed, and have been found in almost all the specimens in larger numbers than the 

 Diatoms and the Radiolaria; they are also the only ingredients that may sometimes be of essential im- 

 portance with regard to the appearance of the specimen, as they bristle out on all sides when the specimen 

 is broken. This is especially the case with station 78, southwest of Iceland, and station 90, between 

 Iceland and Greenland, to a smaller degree with stations 45 and 48, southeast of Iceland; it seems, how- 

 ever, to be quite a casual phenomenon, as neighbouring specimens do not contain any specially large 

 quantities of Sponge spicules. The Radiolaria and the Diatoms are found in the specimens in quantities, 

 being in a fixed proportion to that of the Sponge spicules; if there be few of the latter, only a few 

 individuals of the former will generally be found. Which of the two groups is of most importance is not 

 easily decided; as a rule more Radiolaria than Diatoms are found in the region south of Iceland, and on 

 the ridge between this island the Faroe Island, while to the north the case is the reverse. Upon the whole 

 it may be taken as a rule that the siliceous organisms are found in greater quantity farther off from 

 the land, while near the land they are quite minimal in the specimens; but whether this be owing 

 to the fact that they live in smaller numbers near the land, or to the supply of mineral material 

 being here far greater, is as impossible to decide with regard to these, as it was with regard to the 

 other groups of animals. I have not been able to discover fresh-water Diatoms in the specimens, 

 neither wottld the pointing out of such be of special interest, as we know beforehand that the speci- 

 mens get large supplies of terrigenous material, unless it might also be decided whence they had 

 come, and such a determination would require a more thorough knowledge of the Diatoms than I am 

 possessed of. 



The Ingolf-Expedition. I. 3. 



