Mr . Watt's Observations 
284 
generally well defined, and easily separable from the mass they 
are engaged in ; and often the fibres divide at equal distances 
from the centre, so as to detach portions of the spheroid in 
concentric coats. The transverse fracture of the fibres is com- 
pact and fine grained; the colour black; and the hardness 
somewhat inferior to that of the basaltic glass. When two of 
the spheroids come into contact by mutual enlargement, no in- 
termixture of their fibres seems to take place; they appear 
equally impenetrable, and, as neither can penetrate, both are 
compressed, and their limits are defined by a plane, at which a 
separation readily takes place, and each of the sides is invested 
with a rusty colour. When several spheroids come in contact 
on the same level, they are formed by mutual pressure into 
pretty regular prisms, whose division is perfectly defined ; and, 
when a spheroid is surrounded on all sides by others, it is com- 
pressed into an irregular polyhedron. 
4th. The transition from this fibrous state to a different 
arrangement, seems to be very rapid ; for the centre of most of 
the spheroids becomes compact, before they attain the diameter 
of half an inch. As the fibrous structure propagates itself by 
radiating into the unarranged mass, the compact nucleus which 
supplies its place gradually extends, till it finally attains the 
limits of the spheroids ; and the same arrangement pervades the 
matter comprehended between them. The mass has now 
assumed a compact stony texture, and possesses great tenacity. 
•Its hardness is somewhat inferior to that of the glass from which 
it was formed. Its action on the magnetic needle is very con- 
siderable. Its specific gravity is 2.938. Its colour is black, in- 
clining to steel gray : it is absolutely opaque, and only reflects 
light from a few minute points. Though the divisions between 
