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MINERALOGICAL REMARKS. 287
they differ in their external appearance, are the fame, even in the
difpofition to lofe their property of intumefcing on heating, by this
being performed in a covered veflel *. For it is’clear, though the
learned chemift did not advert to it, that it is exa@tly the fame caufe,
which made the clear and tranfparent fragments of the previoufly
heated pebbles not lofe their qualities on being again placed in the
furnace, which made their matrix remain unafledted by fire when
heated in a clofe veflel, and then be not affected by the blow-pipe :
and I lately faid that the grey matrix was intermixed with red, and I
have {mall fpecimens in which the red predominates; this need
therefore only have had untunicated nuclei (for the red pebbles,
it will be recollected, were quite opake) to be perfectly fimilar, and
it really has; but they are generally tunicated till they become by
exfoliation of the fize of a poppy feed, and it is then difficult to
examine them.
The refemblance of the two, that from near
Kamfchatka and that from Tokay, is ftrikingly alike.
The fofil on which I have been fo diffufe, is not a rare foffil in
this part of Hungary. The matrix forms, according to Mr, Fichtel,
* On this point Mr. Pallas and Mr. Lowitz feem to differ: for the former fays, that
the fragments of the internal part of one of thefe pebbles which-had been heated, gave
the fame appearance, on being again heated, as the pebble itfelf did at firft; whilft Mr.
Lowitz not only fays that the internal part continues clear when in the pebble, but
its fragments on fubfequent heating lofe nothing of their tranfparency.
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