AGATES, CARNELIANS, AND JASPERS. 163 
interspaces between the pendant masses. A cross section of 
two adjacent stalactites at an early stage in their growth 
will show that they are at this stage two nearly cylindrical 
bodies. As they increase in diameter, and so come each 
more within the sphere of each other’s influence, the cross 
section of the two becomes that of two ovoids with their 
pointed ends directed toward each other. Eventually, with 
further growth they unite, and their joint cross section is 
that of an ellipse; and so on, until they become confiuent 
with others, and all the spaces between thein are filled up. 
Hitherto no mention has been made of the fact that 
Chalcedony varies much in translucency, that is to say, in 
purity. The earliest deposited layer in the agate is nearly 
always translucent and colourless, hence Dr Heddle refers 
to this as the Clear Chalcedony Layer. There seems evidence 
to show that this was one of the first chalcedony layers to 
coagulate and eventually to harden. But the layers that 
succeed usually vary much in translucency and, to a certain 
extent,also in colour. As a result, the fact that the Chalcedony 
is deposited in very thin layers at a time is revealed by the 
close alternations of bands of different tints. These range 
from pearly-grey to almost chalky-white in one direction, and 
to lavender, dove-colour, and slaty-grey in the other. The 
chalky nature of these bands usually arises from an admixture 
with some foreign substance, which Dr Heddle, who knew 
more about agates than any one else, regarded as a zeolite 
of some undetermined species. 
Yet another modification calls for remark. At an early 
period in the history of the agate, usually almost immediately 
after the Clear Chalcedony Layer has been completed, there 
seems, in many cases, to have been a temporary pause in the 
deposition of the Chalcedony, and instead of that substance 
there has been a sporadic deposition of minute tufts of some 
mineral, which there are many reasons for regarding as one 
of the tufted zeolites, such as Natrolite. Soon after this 
episode the deposit of silica jelly went on again. This time, 
however, the molecular constitution of the silica was liable 
to certain important variations, to be noticed in more detail 
presently. For the present we need only consider the 
chalcedonic modification. In order to understand what 
