M. Beudant on the FUchstme of Saxo^h^. S6T 
tain that what is naturally formed is always in the same case. 
It is especially very difficult to adapt this explanation to the 
formation of nitrate of potash in certain caverns of calcareous 
mountains, as, for example, in the nitre-mine of MoTfetta in Po- 
land, and in others which occur in many parts of the same 
country. 
On the Pitchstone of Saxony. 
Valley of' Tribisch. — I come now to the Valley of Trihisch^ 
which opens into that of the Elbe, at Meissen, and which is de- 
serving of particular attention, on account of the great masses of 
pitchstone which it presents to the observer. On entering the 
valley by Meissen, the first rock that occurs is syenite passing 
into /granite, like that of Dohna ; but at the distance of three 
quarters of an hour’s walk, a particular kind of porphyry begins 
to appear, of a brown and sombre hue, which includes a great 
number of small crystals of lamellar felspar, sometimes even a 
little cracked, and resembling glassy felspar; brown mica with 
much lustre, also occurs in small hexagonal lamellae, ^hese 
rocks attract the magnet, and have a certain analogy witli some 
varieties of porphyritic trachyte; in some parts, they have a 
tendency to divide into thin folia ; in others, the mass is less 
divisible, and assumes an earthy character. These porphyries 
constitute a great part of the mountains which border this val- 
ley, and continue a great way on ascending toward Freyberg, 
until at last we arrive at arenaceous deposits of argillaceous mat- 
ters, having more or less of a porphyritic structure, (Thon- 
stein, porphyrartiger Thonstein). 
But, in following this valley, we find on its left a small trans- 
verse valley, where the pitchstones more particularly occur. 
They form a pretty large mass of rocks, raised upon a consi- 
derable elevation, and which, from its position, appears to rest 
upon the porphyries just mentioned. In the bottom of the val- 
ley, near the baths which have been erected there, we find an 
argillaceous rock, with a white or reddish basis, which pre-r 
sents spots of a deeper red colour and irregular figure, and in 
which crystals of felspar and quartz are observed here and 
there. These are claystones, (Thonstein), more or* less dis- 
tinctly porph 3 n:itic (Mimporphr, Brong.), perfectly similar to 
