THE DEPOSITS OF THE SEA-BOTTOM. cq 



this region in all other respects; in the two adjacent specimens, nos. 12 and 92, the percentage leaps 

 from 20-5 to 3. In the Greenland specimens the angite is found in comparatively small quantities, 

 varying from 0-5 to 7-5 per ct. without any recognizable regidarity in the distribution. 



Among the rhombic pyroxenes the hypersthene is easily distinguished and conspicuous; it 

 forms prismatic grains with very strong pleochroism, green when viewed longitudinally, and brownish 

 or yellowish red when viewed transversally. As in enstatite and bronzite, the refraction is about like 

 that of augite, while the double refraction is far slighter, also a very characteristic fact. The hyper- 

 sthene has been found in several of the Greenland specimens, but always in small quantity; on the 

 other hand the enstatite and the bronzite that are only little characteristic, more or less colourless, 

 have not been found. The triclinic pyroxenes, aegirine and akmite, on account of their small angle 

 of extinction, can only with great difficulty be distinguished from hornblende, having the same colour 

 and pleochroism as this mineral, nor have they been noticed; moreover there is only a very slight 

 possibility for their being found in the specimens at all. 



The common hornblende is one of the minerals most easily distinguished; it is almost always 

 found in prismatic grains with distinctly marked pleochroism, longitudinally bluish green, transversally 

 yellowish green in different shades. It has been found in almost all the specimens; in the volcanic 

 specimens in very small quantity; in the Greenland ones, on the contrary, it is very common, espe- 

 cially in the northernmost specimens, where, hi no. 31, it rises to 15 per ct. It is probable that wher- 

 ever it is found in the volcanic specimens, it must, as is the case with the quartz and the garnet, 

 have been spread from Greenland or perhaps from Scandinavia. In a few of the volcanic speci- 

 mens the basaltic hornblende was found, dark reddish brown when viewed longitudinally, yellowish 

 brown transversally; it is likely to have originated from Iceland. Other amphiboles have not been 

 observed in the specimens, whether the case be, that they, as the tremolite, are not so easily disting- 

 uished, or they have been very rare. 



Epidote is most frequently seen in prismatic grains with a rather strong refraction and a very 

 strong double refraction; the extinction is parallel to the longitudinal direction of the prisms. The 

 pleochroism is somewhat varying, being less characteristic than it is when seen in a section of the 

 mineral, because the colour of the rays swinging after the axis b, the longitudinal direction of the 

 prisms, is lying between the colours of rays swinging perpendicularly on this axis. When viewed 

 longitudinally the grains commonly appear yellowish green, while, when viewed transversally, they 

 may show all shades from a strong green to light yellowish; the epidote may, however, be more or 

 less colourless, and in such cases it is not easily distinguished from olivine, as its stronger refraction 

 and double refraction are not always sufficient characteristics. Epidote has only been found in the 

 Greenland specimens, and only in small quantities, up to 2-5 per ct, it appears also to be most widely 

 spread in the northern specimens. 



As before mentioned, olivine is not always easily distinguished from augite and epidote. It 

 has been found distributed in the volcanic specimens, but always only in small quantities; the greatest 

 quantity is found in no. 115, close at Jan Mayen, where 2-5 per ct. of olivine is found; it has also 

 been met with in a few Greenland specimens. 



Tourmaline is very characteristic by its strong absorption of light; it is almost always found 



