62 THE DEPOSITS OF THE SEA-BOTTOM. 



to calculate these factors must chiefly be owing to our want of knowledge of the individual currents; 

 that no small quantities of both kinds of material are transported to the regions south of Iceland, 

 may however with certainty be inferred from the comparatively small amount of carbonic acid in the 

 specimens from these regions; if only small amounts of mineral ingredients were deposited, the For- 

 aminifera and the other calcareous organisms would be of comparatively far greater importance in the 

 specimens. One thing is common for the chart on pi. 7 and that on pi. 5, that is the great distribution 

 of a to be sure rather small amount of volcanic material, which is shown in both charts to the south 

 of cape Farewell. This circumstance, I think, is only to be accounted for by the East-Greenland cur- 

 rent, which has an opportunity of receiving some ingredients, partly directly from the northwest coast 

 of Iceland, and partly from a larger afflux, branching off from the Gulf Stream and touching the 

 southwest coast of Iceland, whereupon it unites with the preceding one. 



III. The Ingredients under o-05 mm . 



Apart from the organic ingredients, the finer particles of the specimens, which we now have 

 to examine, are of no special interest, beyond what has already been pointed out, and therefore I shall 

 only mention them quite briefly. 



As to the particles o-o5 mm — o-02 mm in the first place, their smallness, as before stated, does not 

 allow any exact mineralogical determination; they may, sure enough, be referred to the same groups 

 as the larger ingredients, but not with the same degree of exactness. According to a valuation made 

 for each single specimen, they contain the ingredients in about the same ratio of quantity as the pre- 

 ceding size of grains; the quartz is, perhaps, altogether a little more conspicuous, but, as it will be 

 remembered, it was also in the preceding size found in greater quantity than in the coarsest ingredients. 

 For the rest the most expedient treatment of the particles in question is to let them flow out on a 

 plate with a small quantity of water; the lighter particles will then be the foremost ones, while the 

 heavier will remain behind, both parts, however, of course connected by every possible transition. If 

 we now make a preparation of the very foremost particles, and one of the very hindmost ones, those 

 preparations will appear as different as possible. The lighter parts of the specimen will be seen to 

 contain all the siliceous organisms, further the brown, opaque grains, if they consist of tufa or con- 

 glomerated clay, all the colourless glass, and part of the brown glass, that is to say, the more vesi- 

 cular and highly indented grains; on the other hand, if the washing has been made with sufficient 

 caution, not a single double refracting grain will be found; the heavier part, on the contrary, contains 

 all these, as well as all the intransparent grains, further the brown, opaque grains, if they consist of 

 firm rocks, as basalt, and the more compact grains of brown glass. By this division an excellent 

 survey is got of the presence of siliceous organisms and the colourless glass, and with regard to this 

 latter it is seen that the distribution is the same as that, mentioned before with regard to the larger 

 ingredients with the very characteristically distributed four regions where the colourless glass is found 

 in uncommonly great quantities. The colour is somewhat different in the two parts, into which the 



