fo the deposits of the sea-bottom. 



in prismatic form. Longitudinally the colour is rather varying; but transversally the rays are almost 

 completely absorbed, so that the colour is almost black. The refraction and double refraction are not 

 verv conspicuous, they are both a little slighter than in hornblende. The tourmaline has been met 

 with in most Greenland specimens, but always only in small quantities, never surpassing 0-5 per ct. 

 Further it has been found in two specimens, nos. 80 and 75, southwest of Iceland, but also here it may 

 easily have come from Greenland. 



Zircon is distinguished by its large refraction and double refraction, both somewhat stronger than 

 in all the above named minerals; it is almost colourless, and no pleochroism is to be seen, and 

 by its absence it is easily distinguished from epidote, which is most like it with regard to the refrac- 

 tion. Zircon has been found in 12 specimens mostly situated near Greenland or between Greenland 

 and Iceland; it has always only been observed in quite few grains. 



Rutile is easily distinguished by its very strong refraction and double refraction, both much 

 stronger than in zircon. The colour is very strong, reddish or brownish; contrary to what is the case 

 in the tourmaline, the absorption of the extraordinary ray is the stronger, so that the crystals, if 

 lengthened, appear darker longitudinally. Rutile has been found as well in single grains as in small 

 needles in grains of quartz; it has only been met with in 6 specimens near Greenland, or west or 

 southwest of Iceland, and always only in a few pieces. 



To get a general survey of the distribution of the minerals, I have in the chart, pi. 7, stated, 

 as far as possible, the ratio between the volcanic ingredients and the not volcanic ones. This state- 

 ment, however, has rather great difficulties, as the different categories cannot always with certainty 

 be referred to one or the other of the two principal groups. The intransparent grains that have 

 proved themselves chiefly volcanic, have been referred to these ingredients. The brown, opaque grains, 

 on the other hand, have not been counted with, although consisting of chiefly volcanic material, be- 

 cause in part of the specimens they also contain much coherent clay which would somewhat disturb 

 the final result All the glassy ingredients have, of course, been counted as absolutely volcanic, and 

 this, among the double refracting minerals, is also the case with augite and olivine, although these 

 minerals may also be found in smaller quantities in the Greenland specimens. To the not volcanic 

 ingredients have been counted garnet, quartz, and feldspar, although the latter mineral is also often 

 of volcanic origin; further all the other double refracting minerals that are enumerated in the table, 

 with the exception of augite and olivine; the opaque, double refracting grains have not been counted 

 to any of the groups, as they appear in about the same quantity in all the specimens. In the chart 

 three curves have been drawn, one showing the limit of the specimens in which the number of the 

 ratio is over 10, that is to say, where the volcanic ingredients amount to more than 90 per ct of all 

 the ingredients; another curve for the number of ratio 1, corresponding to 50 per ct, and a third 

 curve for the number of ratio o-i, corresponding to about 10 per ct. of volcanic ingredients. It will 

 be seen that the two first curves surround Iceland, the Faroe Islands, and Jan Mayen, in a rather 

 regular way on all sides, although with a pretty well marked greater distance from Iceland on the 

 southeast This is a natural consequence of the fact that an immense mass of material rich in quartz 

 is sent forth from Greenland, which material completely outweighs the Icelandic ingredients in the 



