454 MESSRS. J. PARK AND F. RUTLEY ON THE [Aug. 1 899, 



and consequently give a dark cross. One of these spherulites 

 encloses a small felspar-crystal, the nucleus of which seems to be 

 oligoclase, while the surrounding zone does not conform with the 

 outline of "the irregularly-bounded nucleus, but shows definite 

 crystal-boundaries, which appear to have undergone slight corro- 

 sion. The outer zone may possibly be sanidine. This inclusion 

 contains two prisms of apatite. In ordinary transmitted light the 

 section is «een to contain numerous trichites and longulites, the 

 latter especially as a rule forming narrow bands in the direction of 

 flow (PI. XXXII, fig. 1). A few globulites are also present. The 

 trichites in this section are not built up of globulites, but consist of 

 delicate, opaque, continuous, hair-like rods, tapering towards the 

 ends like eyelashes. A few small crystals of pale green epidote, 

 in one case twinned on (100), occur in this slide. 



H.. Mercury Bay. — This specimen is rather small, but clearly 

 shows the contact of a pale grey or white rock with a dark one, 

 and pellets or spherulites of the latter form coarse dots in the white 

 portion. 



In thin section the dark obsidian-like parts appear, in transmitted 

 light, of a pale yellowish to reddish brown, and are seen under the 

 microscope to consist of spherulites, each spherulite measuring on an 

 average somewhat over ^^ inch in diameter. They are composed 

 of brown imperfectly devitrified glass (or microfelsite of 

 Kosenbusch). Thej have a radiating-iibrous structure, and although 

 some of them give a perfectly circular section, the majority are more 

 or less polygonal, as though pressed together. These spherulites 

 exhibit a dark cross when viewed between crossed nicols, and the 

 cross in some cases becomes considerably deformed during rotation 

 (PI. XXXII, fig. 2), occasionally opening out and forming two dark 

 brushes, as in the interference-figures of biaxial crystals. In 

 addition to these large spherulites much smaller ones occur, deeply 

 stained by ferric oxide. They are sometimes only partially deve- 

 loped, forming a marginal growth on larger spherulites or between 

 them. The light lithoidal portion of the rock shows beautiful 

 perlicity (PI. XXXII, fig. 3), one perlitic crack occasionally sur- 

 rounding four or five other systems of perlitic fissures. This perlitic 

 portion of the rock is pervaded by a microcrystalline to obscurely- 

 small spherulitic devitrification. The large brown spherulites are 

 traversed by very delicate and approximately parallel dark lines, 

 consisting of trichites. Under a ^-inch objective the latter are 

 sometimes seen to form more or less radiating groups of fine 

 opaque hairs, which now and then describe graceful curves, but the 

 majority of the trichites appear to be drawn out in the original 

 direction of flow in the lava. Little crystals and grains, apparently 

 of magnetite, also occur in the brown spherulites, as also a few 

 colourless crystals and grains, which are here and there seen to 

 form the nucleus of a spherulite. The spherulites are optically 

 positive. 



