1905-1906 J 
837 1 
in the rock Th ^ g irre g ularl y sha P^ vesicles 
“ the rock. The central greenish (chloritic) part is usually 
almost isotropic, and is surrounded by a zone of yellowish 
brown material, with a fibrous structure and a radial arrange- 
ment of the component parts.” ° 
Professor Hull remarked that olivine was also present in the 
tock but according to Professor Cole it is by no means an 
abundant constituent of the mass. There is no doubt, how- 
ever, think, that m some places the rock approaches the 
nature of an olmne-dolerite, and, that in such portions of the 
wen 60 1 ' C m ale ° f m ° re C ° mm0n occurren ce than 
P ely siliceous ones. To this analysis must also be added 
iron pyrites, which appears to be distributed in a very irregular 
ashio n th roughout the rock. On the whole, it is not a common 
onstituent, but occasional fragments of the rock may be found 
■containing at least five per cent, of the bright, brass-yellow 
f rys als. In the mam, we may freely accept Professor Cole’s 
description and nomenclature of the rock as a basaltic-andesite 
■or allied to the pyroxene-andesites. Although coarser in 
crystalline structure, the basaltic-andesite of Carnmoney is 
nearly related to many of the Scottish andesites, which are 
compact rocks made up chiefly of labradorite, with a smaller 
proportion of augite, and without olivine ; from these lavas are 
obtained the finest of the chalcedonies, known as ‘Scotch 
pebbles.’ 
2 . The Chalcedony of Carnmoney occurs in large cracks, 
or veins, in the rock. These are sometimes as much as twelve 
inches in width, and from this, the cavities thin away into a 
mere hair’s-breadth. These veins have apparently been formed 
during the consolidation of the lava, for the vein-sides are 
coated, m all degrees of thickness from a mere film to one inch 
with the mineral hullitc, which has been described by Professor 
Cole as “the altered and hydrated glass of the original basaltic 
ground-mass. ’ As the hot magma hardened, the cooling and 
crystallisation of the minerals caused mechanical contracdon to 
lake place, resulting in the formation of large cracks into which 
