q88 
Mr. Watt’s Observations 
structure and the formation by concentric coats. There are few 
radiated substances which are not divisible into concentric frag- 
ments; and as few concentric arrangements which are not 
radiated. Of the first, it may be sufficient to mention haematites ; 
of the second, calcareous stalactites. The tendency to this union 
of structure, may perhaps be produced by the radiation of the 
emitted heat, or moisture, if the solution be aqueous; and the 
divisions of the coats will naturally take place at those pauses 
in the accumulation of particles, which the momentary emission 
of heat necessarily induced. 
If this be allowed to explain the formation of the first series 
of globules which consolidate into the jaspideous substance, it 
will also explain the formation of the larger and more distinctly 
radiated spheroids, w’hich have been already stated to be very 
easily divisible into concentric fragments. They probably were 
also formed round a central point, by the accumulation of thin 
coats ; and the tendency to radiation, which seems almost inse- 
parable from this structure, was perhaps aided by the arrange- 
ment induced by the emission of heat from every part of the 
surface of the spheroids. This mode of formation has the ad- 
vantage of explaining their impenetrability. Had they been 
generated by radii diverging from a centre, their compactness 
must have diminished as their diameter increased ; but, in the 
structure which I have supposed, each coat is composed of 
particles solidly arranged in immediate contact with each other, 
leaving no spaces for penetration. The same progress is rigidly 
observed in the extension of the compact nucleus, which always 
occupies the centre of the radiated spheroids, and finally ex- 
tends to their peripheries. It observes the concentric divisions of 
the radiated part with the greatest precision ;- and the line of their 
