340 [B.N.F.C. 



3. In considering the above interpretations of observed 

 facts, we may class the theories for the origin of hullite into 

 three distinct groups. These are : — 



(i). The Igneous Theory (supported by Scouler, Portlock, 

 and Du Noyer), that hullite is a glassy substance 

 like 'pitchstone' or 'obsidian,' and was probably 

 formed during the last stages of the rock's solidifying. 

 (2). The Mineral Theory (upheld by Hardman, Heddle, 

 Gault, and Lacroix) that hullite is a 'secondary 

 mineral' of the green earth group, and was probably 

 formed during the decomposition of the rock, per- 

 meated by meteoric waters in the ordinary course of 

 rock-weathering, or by hot alkaline waters of telluric 

 origin, under special circumstances. 

 (3). The Altered-Glass Theory (presented by Professor 

 Cole) that hullite is 'the altered and hydrated glass 

 of the original basaltic ground-mass,' or 'a basic 

 glass that has become soft and "gummy" by altera- 

 tion;' it was formed in the first place by igneous 

 fusion, but has suffered subsequent transforming 

 changes. 

 There is no doubt whatever that Professor Cole is correct 

 in his surmise as to the identity of the hullite lining the cavities 

 of the rock, with the material of the ground-mass, but, with all 

 due respect to his fine treatment of the subject, I am inclined 

 to' doubt that hullite was in the first place simply a volcanic 

 glass ; I believe that this substance was not only hydrous in its 

 composition from the first, but that it has not undergone any 

 extensive alteration since that time. In its original condition,, 

 and as still found in certain portions of the rock, the hullite 

 might be more accurately described as a. hydrous, waxy sub- 

 stance, intermediate in its nature between a volcanic glass and 

 a green earth. Professor Cole compares the alteration of the 

 original hullite to its present form, to the alteration of basaltic 

 glass into a green "serpentinous" material ; but, where the hullite 

 is altered, I believe that the change is mostly a physical one, 

 and only to a small extent chemical. The resemblance of 



