M. Delesse on Gilobuliferous Rocks. 173 
would ordinarily have appeared as crystals, has taken the form of 
globules. The excess of silica has acted as an impurity in the 
mass, hindering the formation of regular crystals and leading to 
radiated and globular concretions. It may have acted also by 
causing too rapid a solidification for perfect erystallizations of the 
feldspar. Besides, there was a kind of repulsion between the 
feldspar and the excessively silicious paste, which was superior - 
to the molecular crystallogenic forces tending to form crystals of 
the feldspar, and which by acting upon all sides of the agglom- 
erations, reduced them to spheroidal globules. 
n the globules of normal form in the pyromeride of Corsica, 
—which are characterised by exterior feldspathic layers, the outer 
very quartzose, the inner less so, and a semi-radiated structure 
within—it appears that the exterior was first consolidated, since 
these layers are not onl y very impure, but also support the converg- 
from the centre fill up the spaces between the convergent ones, 
and arise from a solidification nearly cotemporaneous, beginning 
at the centre, where there is often a zoned feldspathic paste, as a 
nucleus, which is very siliceous. The solidification of the feld- 
Spar appears to havea repelling action on the silica, driving it 
either to the circumference or the centre. Thus, cooling from 
the circumference, and cooling from the centre, may occur to- 
gether, or the former may alone characterize a globule, where its 
Structure is made up of convergent needles alone. When con- 
Sisting only of divergent needles, or when throughout zoned, it is 
Considered probable that the solidification took place simultane- 
ously throughout. The silica fills all the interstices between the 
: Idspar heedles and zones; it was solidified after the feldspar as 
i granite. The needles or conoids usually contain a quartz nu- 
Cletls, so that they are analogous in structure to a globule ; the so- 
lidification beginning at the surface, the excess of silica was driv- 
®n to the interior of the conoid. 
Nee of fissures. But in the liquid or pasty state, the circum- 
— are different, especially as a process of desiccation may 
mai been in progress ocks of aqueous origin often contain 
Nereti 
that have resulted from a desiccation of the nodule after the ex- 
Was solidified. They may be argillaceous, silicious, calca- 
Common indifferent deposits, especially the chalk, as the & 
Sig » especially ’ 
Persteine or Achilleum eotiaie of the chalk of the Isle of Moen. 
