178 Miscellanea. 
present distinct traces of the obtuse octohedron, the same with a 
short four-sided prism interposed between the two pyramids, and 
the latter of these with various truncations of its angles and edges. 
The specific gravity of some picked crystals was 67753. A careful 
analysis of this tin-stone gave as its constituents— 
Peroxide olstimi a. vdsenautensasesns isons decdveeeeas QORaO 
iReroxide cofcimomipesseacneckicsaiaaaiismecanenice Gaeta 
SILI Le shia et claehe eats sete Mee Siies sd ae avondale Oe 
oy 
98°51 
The greater number of the minerals here enumerated are men- 
tioned by Mr. Weaver in his reports to Government on the district, 
and which are to be found in the Transactions of the Royal Dublin 
Society ; but some of them, the author believes, have not been 
noticed before, at least he has seen no published account of the 
occurrence in this locality of platina, titanic iron, sulphuret of 
molybdenum, topaz, zircon, the small magnesian garnets, or augite. 
Hence it seemed interesting, while noticing these, to collect into a 
uniform and, as far as possible, complete list, all the scattered 
notices of the mineral wealth of this particular district, which are 
epe found in Mr. Weaver's papers already referred to, and else- 
where. 
The principal point, however, with respect to the examination of 
these minerals, which appears to merit further and more particular 
attention, is the fact of the existence of tin-stone in such consider- 
able quantity in these auriferous streams: a fact which would seem 
to indicate the probable existence somewhere in the surrounding 
district of masses of the ore of this valuable metal of great extent, 
and possibly forming the continuation, on this side of the Channel, 
of those vast deposits which have contributed to furnish occupation 
and support to the inhabitants of Cornwall for more than two 
thousand years * 
New Tueory oF Poxrar Licuts. By J. A. Broun, Esa. 
Mairan, and, more lately, Dalton, have explained this phase of 
the aurora by a hypothesis of polar beams, long fiery rods of solar 
atmosphere, according to the one, of red-hot ferruginous particles, 
according to the other, seen in perspective, as they lie in the direction 
of the magnetic force. A little acquaintance with the phenomenon— 
the rushing and tilting of the beams against each other, one beam. 
occasionally rising from the horizon, passing through the centre of 
the crown and beyond it—would show the improbability of this 
* Transactions of the Geological Society of Dublin. 
