386 Scientific Intelligence—Botany and Zoology. 
exhibit a crystalline arrangement, like the lines in sapphire, calcareous 
spar, and other bodies, and have doubtless been produced during the 
conversion of the quartz into opal by heat, under the peculiar circum- 
stances of its formation. In some specimens of common opal, the 
structure is such as would be produced by kneading crystalline quartz 
when in a state of paste. The different colours produced by those pores 
arise from their different magnitudes or thickness ; and the colours are 
generally arranged in parallel bands, and vary with the varying obli- 
quities at which they are seen— Athenwum, Report of Brit. Assoc. 
6. On Crystals in the cavities of Topaz, which are dissolved by 
heat, and re-crystallize on cooling. By Sir David Brewster.—Sir 
David gave a brief notice to the British Association of the discovery 
which he had made, about twenty years ago, of two new fluids in the 
crystallized cavities of topaz, and other minerals, One of these fluids 
is very volatile, and so expansible, that it expands twenty times as 
much as water with the same increase of temperature. When the va- 
cuities in the cavity which it occupies are large, it passes into vapour ; 
and in these different states he had succeeded in determining its re- 
fractive power, by measuring the angles at five feet. Total reflection 
takes place at the common surface of the fluid of the topaz. The other 
fluid is of a denser kind, and occupies the angles and narrow necks of 
cavities. The cavities, however, in which the soluble crystals are con- 
tained, are of a different kind. They (viz. the cavities) are im- 
perfectly crystallized, and thus they exist in specimens of topaz which 
contain the cavities with the two new fluids; they contain none of the 
volatile and expansible fluid, which is doubtless a condensed gas. The 
crystals which occupy them are flat and finely crystallized rhomboids, 
When heat is applied, they become rounded at their edges and angles ; 
and soon disappear. After the topaz has cooled, they again appear, 
at first like a speck, and then re-crystallize gradually, sometimes in 
their original place, but often in other parts of the cavity,—their place 
being determined by the mode in which the cooling is applied. 
BOTANY AND ZOOLOGY. 
7. Distribution of Plants on Mount Canigou, Eastern Pyrenees.— 
In reporting to the Academy of Sciences on a table of the limits of cer- 
tain plants on the western slope of the Canigou, presented by M. Massot 
of Perpignan, M. Adolphe Brongniart made the following observations : 
—M. Massot’s table gives the height above the level of the sea, of the 
upper and lower limits of many of the species constituting the remark- 
able vegetation of the Canigou, which forms the eastern extremity of the 
chain of the Pyrenees. The table is so much the more interesting for 
botanical geography, from containing the limits of many plants which 
had not generally attracted attention in this point of view, and which, 
although less striking to the eye than forest trees or cultivated species 
covering large surfaces, nevertheless contribute, by their combination, 
to impart to each zone its own particular aspect of vegetation. After 
enumerating forty-two species, which he had observed on the summit of 
the mountain, at a height of 9137 English feet, the author indicates the 
lower limits of some of these species, and the upper limits of other plants 
