208 
NOTES ON A ROCK FROM NEW ZEALAND. 
slightly thicker at the ends. They evidence by the positions 
in which they lie in the rock the motion which was taking 
place in the mass after they separated out. They form bands 
and streams heaped up where they encounter a larger crystal 
and are occasionally perfectly irregular in their distribution. 
hi addition to these microliths there are minute roundish 
bodies which in many cases seem to be the transverse sections 
of the first named bodies, but in others they appear as if 
they were strung together on a fine string forming the so- 
called Margarites. These are frequently of considerable 
length and are curved in various directions through the 
section. 
The mineral nature of these minute bodies is very un¬ 
certain; they do not appear to show any definite crystal shape, 
and the points of the longer microliths show no signs of 
planes. They are not doubly refracting but remain quite dark 
between crossed Nicols. 
In many places several strings of minute granules are 
attached at one end to an opaque grain, probably of magnetite. 
The splierulites are mostly hollow, and though probably 
this is due in a few cases to the central parts having broken 
out in grinding, a good many are apparently hollow in the 
rock itself. They are rather imperfectly seen in my section, 
as this is somewhat thick, but appear to be composed of 
threads of doubly refracting substance roughly radial in 
position, but not so regularly as to show any black cross 
between crossed Nicols. The polarisation is irregular and 
not very marked. 
The spherules are in many cases surrounded by a clear 
yellow margin, which, however, is seen, when a high power is 
used, to be fibrous and doubly refracting in character, and to 
be the ground, so to speak, in which the more opaque 
elements of the splierulite are imbedded. The microliths of 
the glassy base seem in some cases to be visible within the 
spherule, but in other cases they appear heaped up on its 
outer edge as if they had been driven against it by the flow 
of the lava. 
The larger crystals which occur porphyritically are felspar, 
hornblende, and the strongly dicliroic rhombic pyroxene 
which is usually called liypersthene. 
The hornblende occurs sparingly and is of the normal 
olive brown colour. The crystalline fragments occasionallv 
show the cross section of the prism, with the cleavage traces 
intersecting at the usual angle. The long and narrow 
sections extinguish at varying angles with the cleavage traces. 
