1905 - 1906 .] 
339 
the th T t SeC ° 7 mmera1, and dassed k as a member of 
e chlorito-ferruginous group or green earths. As far back as 
the year 1837, however, Dr. Scouler described it as a ‘pitch- 
stone, ^ or volcanic glass, and in 1843 General Portlock called 
1 an obsidian. It is of interest to trace the history of geo- 
ogical opinion concerning hullite from these earliest references 
to those of the present day. In the years 1837-1843, it was 
regarded as a volcanic glass, which had been exuded into the 
“ lava, cooled. About the year 1868 this opinion 
U t P ^ Id b l' 1 G - V ' du N °y er > but ten years later Hardman 
departed entirely from this view, as we have already stated 
escribing it as a secondary mineral of the green earth variety.’ 
n 1879, as Professor Cole has pointed out, Dr. Heddle, of St 
Andrews, supported Hardman in his claim for the retention of 
! aa a definite mineral species. It is here worthy of 
notice, that Heddle’s views concerning the origin of such 
green earths underwent a complete change; in 1871 he re 
garded such minerals as contemporaneous with the last stages of 
coohng in the early history of the lavas in which they are 
nd whereas in his “Mineralogy of Scotland,” written at a 
tion r, Ti f’ u* d6SCribeS the same minerals as decomposi- 
tion products of the weathering lava. In the same year (1879) 
“ , au t ’ of BeIfa st, took up this idea, that hullite was a 
thart Ty , mmera1 ’ and accounted for its origin by supposing 
that it was deposited, along with chalcedony and other siliceouf 
necT ‘ S ’ n h0t aIkaHne Spri ^ s wbicb arose in the volcanic 
The h ? n§ n, a r er V C31liC f0rces had s P ent their vigour.’ 
The hot alkaline water acted on the rock sides and penetrated 
ground of the rock, dissolving mineral matter from the 
mass, and ^-depositing it in the gas-vesicles and veins. In 188; 
hullite was again examined, on this occasion by Lacroix, who 
also determined it to be a secondary mineral related to the 
decomposition-products of olivine. Latterly, in 1895, Professor 
Cole reviewed the opinions of Hardman, Hull, Heddle, and 
Lacroix, and, setting aside the idea that hullite is a ‘secondary 
mineral at all, described it as ‘a basic glass that has become 
soft and gummy ’ by alteration. 5 
