1905 - 1906 .] 
547 
occasionally minute tufts of zeolites may be found in similar 
positions. There is no> doubt that cold, surface-waters, charged 
with carbonic acid, can remove calcium carbonate from the 
rock, and dissolve existing crystals of calcite, carrying away, in 
the form, of bi-carbonate, considerable amounts of that mineral, 
and re-depositing it in other places. The formation of zeolites- 
from felspar and from existing zeolites takes place in a similar 
manner, but tO' a much less extent ‘ and the formation of 
chalcedony in this fashion appears to' be a very rare occur- 
rence. There is also- no doubt that these reactions, resulting in 
the growth of calcite, hydrated silicates, and various forms of 
silica, would go on at a much faster rate, and to a much greater 
extent, if the cold meteoric waters were replaced by hot alkaline 
waters of telluric origin. These actions have their place in 
nature ; but when we consider the molten magma from which 
certain lavas have been formed, containing water under immense 
pressure, and at a temperature far exceeding that of any 
solfataric water, we come to the conclusion that the residual 
waters of such magmas contained large quantities of silica, 
silicates, and carbonates in solution. As the temperature fell, 
the dissolved mineral matter would be secreted and deposited 
in the veins and cavities, in a definite sequence, according to 
the nature of the dissolved elements. It is natural that such 
secondary minerals should bear some chemical relation to the 
primary rock-forming minerals, because both are formed from 
the same magma. 
The rock-forming minerals of the Carnmoney basaltic 
andesite are augite, labradorite felspar and magnetite. Augite is 
composed mainly of calcium, magnesium, aluminium, and iron 
silicates, the silica amounting to 47-48 per cent. In the hullite 
we find hydrous silicates of the same elements, iron being the 
preponderating element. When the water of hydration is 
omitted from the analysis the silica amounts to almost 46 per 
cent. The primary augite and magnetite have thus a second- 
ary counterpart in the hullite. Labradorite is composed of 
aluminium, calcium, and sodium silicates ] the silica amounting^ 
t°‘ 5 2_ 53 P er cent. In natrolite (the most common zeolite in 
