^ THE DEPOSITS OF THE SEA-BOTTOM. 



The size of grains in the sand is of course closely connected with the amount of the coarser 

 ingredients in the whole specimen; where they are found in greater numbers, the coarser grains will 

 also be predominant in the sand, and it will chiefly get sizes rising towards o-5 mm ; if, on the other 

 hand, the coarser ingredients be wanting, or if they be only found to a small amount, the sand will 

 be fine, which latter case thus will be predominant in the deeper regions far from land. 



The percentage of the magnetic ingredients is closely connected with the more or less volcanic 

 nature of the sand, the larger part of the volcanic ingredients being attracted by the magnet, while 

 this only applies to a very small part of the other ingredients. Most of the intransparent particles 

 are attracted, as also almost all basalt and tufa, but not the basaltic glass, nor of course the glass 

 rich in silica. Of the minerals the most ferruginous varieties of augite and hornblende are magnetic, 

 but only to a small degree. What especially reduces the value of the determination of the magnetic 

 ingredients is the circumstance that most of the coherent clay that may be found in the sand, is also 

 attracted by the magnet, and the amount of this clay is not dependent on the nature of the sand 

 according to its locality, but is quite casual. 



The intransparent ingredients may consist of grains of magnetite or perhaps pyrite; but this, 

 I think, is only the case with the smaller part of the ingredients. The greater part I take to be 

 made up of compact, very ferruginous basalt, which in the size of grain in question proves absolutely 

 intransparent; finally may also some of the volcanic tufa and the transformed Foramiuifera fall under 

 this category. The intransparent grains pass evenly into the brown, opaque grains; to this latter 

 category I have referred the grains, when only a single corner of them was transparent. The per- 

 centage of the intransparent grains is on an average upwards of ten in the volcanic regions; it is 

 largest between Iceland and the Faroe Islands, where it rises commonly over 20, up to 29 in no. 139. 

 The smallest amounts are found in the purely Greenland specimens , the very smallest one in no. 38 

 with 0-5 per ct; in these specimens I suppose all the intransparent grains to be made up of magnetite. 

 For the rest no great regularity is found in the distribution of these grains, and therefore I shall not 

 here enter upon a closer examination of this distribution. 



The brown, opaque grains form the most comprehensive class of the ingredients, most of the 

 basalt, tufa, and hardened clay, besides more impure, volcanic glass, and part of the transformed For- 

 aminifera falling under this heading. On account of this heterogenousness the distribiition is, of course, 

 very irregular; the amount is largest in the most volcanic districts, up to 61-5 per ct. in no. 78; smallest 

 in the Greenland regions, with 0-5 per ct. in no. 29; the largest amount is here surely made up of 

 conglomerated clay. The category passes very evenly and gradually into the next one, the brown 

 glass, so that the classification in many instances is rather difficult. 



Contrary to the two preceding categories that of the brown, volcanic glass is a very uncom- 

 pounded one, even if it be not distinctly bordered on one side from the brown, opaque grains, on the 

 other from the colourless glass or the other, differently-coloured sorts of glass. Consequently the 

 distribution is rather regular, and put down in the chart, pi. 6. In viewing this chart we shall im- 

 mediately perceive at great difference between it and the charts, giving the distribution of all the 

 volcanic ingredients. While in the latter as well Iceland as the Faroe Island and Jan Mayen are 

 centres of distribution, and everywhere give volcanic material, the distribution here takes only place 



