S46 M. Beudant on the Opals of Hungary, 
we not led to a different conclusion by the nature of the ma- 
trix. 
The different varieties of opal-jasper occur most commonly 
in the trachjtic conglomerates; and particularly in the more or 
less altered pumice, where they appear to be formed like 
hints in the midst of chalk. These kidneys are often pre- 
cisely defined, and very distinct from the deposit which enve- 
lopes them. This is the case with the ferruginous opal-jasper, 
and with the white opaquje opal, into which they pass in a mi- 
neralogical sense ; but sometimes the liidneys appear to be con- 
tinuous with the enveloping mass, and to be nothing else than 
the result of a siliceous infiltration into its substance. This last 
case presents itself in the kidneys of ferruginous *opal-jasper, 
formed in the midst of deposits ol‘ oxide of iron or of argillo-fer- 
riiginous rhatter, and also in the waxy and earthy opal-jasper. 
These two last varieties form kidneys in the midst of pumicose 
matters, which have been much altered, extremely divided, 
and reduced in some parts to an earthy and homogeneous state. 
These matters, like the earthy jasper, have a yellowish-white or 
greenish- white colour, and assume, on inbibing water, a deeper 
tint, as well as a little translucidity. On seeing this position 
(gisement), it is impossible not to imagine that these very at- 
tenuated matters have been posteriorly filled up by siliceous in- 
filtrations, which have consolidated them a little here and there, 
and given rise to earthy opal-jasper ; while, in other parts, be- 
coming more abundant, they formed the waxy opal-jasper. If 
this mode of formation is not that which has been followed by 
nature, it must at least be owned that appearances are much in 
its favour; for the mass of earthy opal-jaspeiv* sometimes con- 
tains numerous angular cellules, of which some have remained 
empty, while others are found filled with true yellowish opal, 
nearly transparent, and of the same tint of colour as the waxy 
jasper, which is found by its side, in kidneys of greater or less 
size, and forming part of the same mass. This penetration 
of the pumicose -debris by a siliceous j uice, is submitted to exa- 
mination, in the porphyritic pumice-conglomerates wdiich we have 
already described ; and if it has taken place in such large masses, 
we may, with equal propriety, conceive it a fortiori to have 
liaken place in small masses. 
