Mr. Watt’s Observations 
298 
in which the radii have entirely disappeared, and the whole mass 
has become compact. It is probable that the entire formation of 
oolithi and pisolithi is owing to the same cause ; and that they 
are prevented from ever arriving at great size, by the union of 
their surfaces, and their subsequent consolidation into compact 
limestone, into which they are continually found to graduate. 
Hitherto, I have selected instances from substances which 
have an undisputed claim to an aqueous origin. I shall now, on 
the authority of Dolomieu, instance a similar arrangement, in a 
substance respecting the origin of which theorists are not agreed. 
A species of petrosilex is found in the Val de Nido, in Corsica, 
which contains radiated petrosiliceous glands, from half a line 
to an inch in diameter. These glands only differ from the basis 
by their radiated structure, and their colour; and appear to 
indicate very clearly, that the rock was subjected to a species of 
arrangement which, if it had been completed, would have 
changed its nature, and probably would have rendered it por- 
phyritic; for Dolomieu observes, that the centre of the glands 
was often occupied by a small crystal of feldspar.* The extra- 
ordinary rock called the globular Granite of Corsica, is an 
analogous instance. It is composed of crystals of hornblende, 
feldspar, quartz, and mica, in confused aggregation ; and in this 
basis are immersed spheroids, about an inch and a half or two 
inches in diameter, composed of concentric alternate coats of 
quartz and hornblende. The centre is principally occupied by 
hornblende; this is surrounded by a zone of quartz. These 
spheroids are radiated to the centre. There can be little doubt that 
this rock is merely the result of interrupted crystallization ; and 
that, if the process of arrangement had continued, this structure 
• Dolomieu. Journal de Physique , 1794? P a £ e 260. 
