430 Scientific Intelligence. 
2 In composition it differs little from iolite, affording silica 50-90, 
alumina 32°38, magnesia 8:01, lime a trace, protoxyd of iron 2°34, 
water 6°73, manganese a trace. 
5. Castor and Pollux, two new minerals; by Brerrnaver and 
Pratrner, (Pogg. Annal., Ixix.)—These minerals occur in granite on 
the Island of Elba. Castor has a vitreous lustre and rough surface, 
and is transparent and colorless, with two axes of double refraction and 
two cleavages inclined at an angle of 1283 or 129 degrees. Hardness, 
a little above adularia; specific gravity 2°3801—2-401. Fuses with 
difficulty before the blowpipe to a limpid colorless glass, coloring the 
exterior flame red. Composition according to Plattner, silica 78:012, 
alumina 18°856, peroxyd of iron with traces of manganese 1-613, lithia 
with traces of potash and soda 2-760 100-241. 
Pollux resembles castor in crystallographic and physical characters, 
except that there are only traces of cleavage, and it has the specific grav- 
ity 2°868 to 2°892. Heated ina tube, water is disengaged. Before the 
blowpipe the edges are rounded to a blebby enamel, and it colors the 
exterior flame reddish yellow. It contains 46-2 per cent. of silica, with 
16°5 of potash, 10°47 of soda and 2°321 of water. There was a loss in 
6. Pleochroism.—Haidinger has applied the term pleochroism to 
the property pertaining to many crystals, of presenting different colors 
in different directions. e terms dichroism and trichroism heretofore 
used are too limited in signification, as different colors are presented in 
some species in more directions than three. / 
7. Russian Geology, (Proceedings of the Acad. Sci. of St. Peters- 
burg; L’Institut, No. 681, Jan. 20, 1847.)—M. HeLMERsEN has ready 
for publication an extended account of the geological observations 
which he has made in his different journeys through the departments of 
Livonia, Estonia, Pskov, St. Petersburg, Novgorod, Tver, Moscow, 
Toula, Kalouga and Orel; and in the summer of 1845, he made a tour 
h the facts 
there presented and give greater completeness to his description of the 
e. 
8. On Slaty Cleavage in North Wales ; by BIL Suarpe, (Geol. 
Soc., March, 1844; Quart. Journal Geol. Soc., No. 7, p- 309,)—In 
the course of a valuable article on the geology of North Wales, Mr. 
Sharpe makes the following statements with regard to slaty cleavages. 
In North Wales, not only in the Cambrian but also in the Lower Silu- 
