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hullite to a chloritic mineral I regard as an original structure. 
It is closely related to the green earths, celadonite and 
chlorophseite, which form the 'skin’ of many agates, and which 
originated in quite a different manner from the “serpentinous” 
green earths; the latter are decomposition-products, and the 
former are contemporaneous formations of the lava. Professor 
Cole compares the coating of hullite in the vesicles to 'lava- 
stalactites’ on a small scale, 'the glassy matrix of the lava having 
oozed out under pressure into any cavities it could find;’ but 
these 'stalacites’ and spherical crusts of hullite possess a fibrous 
structure similar to the reniform or spherical growths of 
haematite and chalcedony, and I believe that the hullite was 
formed, to a great extent, under the guidance of active crystal- 
line forces.. The highly vesicular nature of the rock suggests 
the probability that that much water was present in the hot 
magma, and that the formation of the hullite was not purely an 
igneous action, but rather intermediate between igneous, and 
hydro-thermal. 
4- The extensive literature concerning hullite has rendered 
Carnmoney Neck historic in the annals of mineralogical geology, 
but of the chalcedony and other minerals found in the cavities of 
the rock, very little has been said or written. The Survey 
Memoir, for example, merely mentions the fact that 'a good deal 
of chalcedony occurs throughout the mass, and occasionally 
fills the vesicles.’ Gault investigated the 'chalcedony and other 
siliceous minerals’ generally, but did not give any detailed de- 
scription of the type-vein containing them. The typical vein 
at Carnmoney consists of three distinct layers, or groups of 
layers, more or less intergrown, and representing three con- 
secutive stages in the deposition of the mineral matter filling 
the vein. These are: — 
(1). The Hullite Layer, consisting of hullite in varying 
degrees of thickness from, a mere film to a crust, 
which is never more than an inch in measurement! 
The usual thickness of this mineral is one-sixteenth 
to one-eighth of an inch. The hullite coats the 
rock-sides, and was the first substance deposited in 
the vein. 
