340 
M. Beuilant mi ike Opals (f Hungary. 
or less triturated, more or less altered, and as they are more or 
less numerous in the paste or basis which results from their com- 
minution. 
The most elevated parts of these mountains, those which are 
nearest the centre of the chain, and which immediately rest upon 
the trachyte in situ.^ are in general composed of large blocks 
piled upon one another, and between which there exists a finer 
conglomerate, a coarse paste, resulting from their mutual friction 
and their decomposition. The more advanced and also lower 
hills, contain in general smaller and more altered fragments, and 
the paste is always extremely abundant ; it is often confounded 
with the fragments which it includes; and occurring sometimes 
absolutely simple in large spaces, it becomes impossible to dis- 
tinguish the arenaceous nature of the deposit. In this case, we 
find either homogeneous rocks, with an earthy, smooth, or very 
large conchoidal fracture, which presents various tints of yellow, 
red, or brown, or porphyritic rocks, which often even present 
all the characters of the rocks produced by crystallization. 
These last varieties are of various natures ; some of them pre- 
sent, at first sight, the appearance of a porphyry, because they 
are marked with a great number of small vesicular cavities, each of 
which is filled with a white earthy matter. The others have more 
deceitful characters, because they contain fragments of felspar, or 
even entire crystals, which often appear to hav^ been formed di- 
rectly in the earthy mass. These are the rocks which have par- 
ticularly deceived naturalists regarding the true nature of the 
matrix of opals, because, on seeing them isolated in collections, 
it was not possible to know that they are only infinitely small 
portions in the midst of the mass of very distinct conglomerates. 
It is not so when they are observed in situ. They are seen at 
the first glance, evidently connected with parts, where the paste, 
although abundant, incloses very distinct fragments ; and hence 
it is. impossible not to remark the intimate connection of these 
fine deposits vvith the coarser conglomerates which compose the 
greater part of the mountains. 
The veins or nests of opal occur every where in these masses : 
they are found equally at the surface, as deep in their substance ; 
and nowhere have I been able to observe, as Fichtel asserts, that 
