346 
[B.N.F.C. 
On, the whole, I feel convinced that such deposits of 
chalcedony in volcanic lavas, and this one at Carnmoney in 
particular, are contemporaneous formations of the rock, and 
that they were formed during the last stages of the lava’s cool- 
ing and drying. Furthermore, I am, constrained to believe that 
the zeolitic or calcitic layer, and the siliceous contents of these 
veins and cavities, owe their origin, not to the decomposition of 
the mother-rock, but to the final process of its construction. In 
all probability the water present in the hot lava pjayed an 
important part in the formation of these minerals. We may 
look upon this process of vein-filling in lavas as an example of 
the thorough economy so often exhibited in Nature. During 
the consolidation of the lava contraction took place, and the 
cracks or veins were formed. These were points of weakness 
in the rock — real wounds — and Nature immediately set about 
their healing. The residual magma — the very life-blood of the 
lava we might call it — was secreted into- these rents, impelled 
more or less by physical forces, but, nevertheless, continually 
guided within itself by active crystalline- energy. The hullite, 
calcite, zeolites, and chalcedony were deposited each in its 
order, and when the rock was cold and dry these minerals stood 
each in its place, and each ready to play its own part as a 
necessary portion of the solid earth. There is an unbroken 
sequence in the mineral matter from the main constituents of 
the lava to- the chalcedony in the centre of the veins. Professor 
Cole has shewn that the hullite plays the part of a true ground- 
mass in the intercrystalline spaces of the rock. Lacroix ob- 
served that the hullite has included in its formation minute 
crystals of felspar and magnetite ; also- small crystals of calcite. 
The calcite and zeolites follow upon the hullite, and finally the 
chalcedony, which in its growth has included crystals of calcite, 
and zeolitic matter. 
7. That the calcitic or zeolitic layer of the veins is often 
much weathered I have already mentioned, and very often, its 
former presence can only be inferred from the hollow pseudo- 
morphous cavities in the chalcedony. This calcite has in some 
cases been re-deposited in other portions of the veins, and 
