1905-1906] 341 



hullite to a chloride 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 rilling 

 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. 



