
xs 
Part IL § iv.] MICROSCOPIC CHARACTERS OF ROCKS, 101 
simplest are extremely minute drop-like bodies or globulites. Quite 
isotropic, they are sometimes crowded confusedly through the glass, 
giving it a dull or somewhat granular character, while in other cases 
they are arranged in lines or groups. Gradations can be traced from 
spherical or spheroidal globulites into other forms more elliptical in 
shape, but still having a rounded outline and sometimes sharp ends. 
These were termed by Vogelsang Longulites: There does not appear 
to be any essential distinction, save in degree of development, between 
these forms and the long rod-like or needle-shaped bodies which have 
been termed mcroliths (Belonites). Existing sometimes as mere simple 
needles or rods, these microliths may be traced into more complex 
forms, sometimes pointed, sometimes toothed at the end, straight, 
curved or coiled, smooth or striated, at one time solitary; at another 
in groups. It is sometimes possible from their association to 
determine to what minerals microliths belong. Augite, hornblende, 
apatite and. felspars all oceur in-these rudimentary forms. In most 


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Fic. 9.—MiucronITus oF THE PITcHSTONE OF ARRAN, MAGNIFIED 70 Diameters. (See p. 140.) 
cases the microliths are transparent and colourless, or slightly tinted, 
but sometimes they are black and opaque, from a coating of ferru- 
ginous oxide, or only appear so as an optical delusion from their 
position. Black seemingly opaque hair-like twisted and eurved 
microliths, termed ftrichites, occur abundantly in obsidian. Good 
illustrations of the general characters and grouping of microliths are 
shown in some vitreous basalts. In Fig. 8, for example, the outer 
portion of the field displays crowded globulites and longulites, as well 
as here and there a few belonites and some curved and coiled micro- 
liths. Round the augite crystal these various bodies have been drawn 
together out of the surrounding glass) Numerous rod-like microliths 
diverge from the crystal, and these are more or less thickly crusted 
with the simpler and smaller forms.’ In Fig. 9 the remarkably 
beautiful structure of an Arran pitchstone is shown; the glassy base 
being crowded with minute microliths which are grouped in a fine 
brush-like arrangement round tapering rods. In this case also we 
1 Geikie, Proc. Roy. Phys. Soc. Edin, y. p. 246, Plate v. Fig. 5. 
