THE DEPOSITS OF THE SEA-BOTTOM. cc 



from Jan Mayen and Iceland, and from the different parts of the latter island to a very unequal 

 degree. Certain regions produce large percentages, while others only yield little or perhaps nothing 

 at all; the latter regions are especially gathered in two districts, a smaller one on the southeast coast, 

 and a larger one round the large northwestern peninsula, while the southwestern and the whole 

 eastern part of the island yield large quantities that spread rather evenly outward, and disappear 

 more and more towards the outer borders; while the ridge between Iceland and the Faroe Islands 

 seems to be of no importance, that between Iceland and Greenland occasions a somewhat larger per- 

 centage than the surroundings, chiefly, I suppose, on accout of the earlier mentioned masses of pumice 

 originating from the ridge. The influence to be traced here, is, however, minimally small in compar- 

 ison with what is the case with regard to the coarser sizes. The distribution appears also to be 

 rather great southwest of Iceland, though it is not easy to account for this fact. The nature of the 

 brown glass is somewhat different on the different localities; sometimes it is quite without vesicles, 

 and then the grains are irregularly angular; sometimes it is filled with very small vesicles; more 

 frequently, however, these vesicles are in size equal to or larger than the grain itself, so that this is 

 limited by inverted circle planes. Sometimes the vesicles are distinctly lengthened in a certain direction, 

 they may also become linear, twisted in different directions; this latter, however, is not so frequent 

 here as in the colourless glass. Small crystals are often found as grains in the brown glass; but on 

 account of their smallness they cannot be determined. 



The red, yellow, and green volcanic glasses may be interpreted as subordinate varieties of the 

 brown glass, with which they are also connected by transitions, and they have the same distribution; 

 they are all only found in very small quantities in the specimens, only rarely rising to one per ct The 

 yellow glass has been found in 10 specimens divided all round Iceland; the green glass has been 

 found in 16 specimens, of which some, strange to tell, are situated at the west coast of Greenland, 

 where otherwise volcanic ingredients are not found. Perhaps the grains referred to this category, are 

 not at all volcanic glass, but chlorite or a similar mineral; chlorite especially, which is always very 

 slightly double refracting, and in certain varieties even wants double refraction completely, will in a 

 grain-preparation scarcely in any way be distinguishable from green, volcanic glass. The red or red- 

 brown glass is the most widely spread of the three varieties; it is found in 33 specimens, exclusively 

 in such, in which brown glass is also found; it is met with in especially large quantity in the speci- 

 mens northeast of Iceland, and between Iceland and Jan Mayen; in the specimens closest to the latter 

 island, it may perhaps have its origin from this island. 



The colourless glass is also connected with the brown glass by some transitions in the colour; 

 far the greater part, however, is rather different from it That the colour is completely wanting makes 

 this glass rather difficult to be distinguished in the preparations, especially as it contains no trace of 

 any double refracting substance, so that it cannot at all be seen in polarised light The refraction is 

 about the same as that of the Canada balsam, only slightly smaller, while for the brown glass it is a 

 little greater, which we may observe by putting on a strong objective, and then raising and lowering 

 the tube a little; at the edge of each transparent grain we shall then see a whitish shadow, and if 

 this passes in over the edge when the tube is lowered, the grain is more slightly refracting than the 

 Canada balsam, while it is stronger if the opposite case takes place. At grains that have exactly the 



