324 Intelligence and Miscellaneous Articles, 



vol. iii. p. 29) = 10"-18621268w°- + 0*0185384408^, the above 

 month-duration actually occurred about 1000 b.c. Assuming, with 

 Professor Adams, only the half of the above coefficient, the aforesaid 

 month-duration occurred about 2200 b.c This period having actu- 

 ally been observable by man, and the years being twenty-five, render 

 the above German remark very interesting. 



If, in the Gregorian calendar, 999 years had been made a com- 

 plete cycle, disallowing the leap-day of 100, 200, 300, 500, 600, 

 700, 900, there would have been introduced i(996) — 7=242 leap- 

 days, so that the average year =365*242242242, very nearly true 

 = 365 d 5 h 48 m 49 s *792 (^49-^). Thus the Gregorian cycle- 

 epochs would have been 1600, 2599, 3598, 4597, 5596, &c. 



S. M. Drach. 



March 1863. 



ON A PSEUDOMORPH OF MICA AFTER CORDIERITE*. 

 BY DIRECTOR HAIDINGER. 



This curious specimen was lately found at Griinburg (Upper 

 Austria) in a granular white orthoclase, intermixed with small 

 granules of quartz, small icositetrahedra of reddish-brown garnet, 

 and minute and scarce particles of iron- and copper-pyrites. The 

 crystals are dodecagonal prisms, with a terminal plane vertical to 

 the principal axis ; they are 2 inches long and 1 inch in diameter, of 

 a dark-green colour, reminding one in their outward aspect of pinite, 

 gigantolite, or chlorophyllite. Their completely crystallized portion 

 is in immediate contact with greyish-white diaphanous quartz. The 

 planes by which they are in contact with the orthoclasic matrix are 

 irregular and not well denned. In their interior the whole of the 

 cordierite has been metamorphosed into mica, whose lamellae lie 

 parallel to the surface of the crystals. Chev. C. von Hauer, who has 

 analysed them, found their constituent elements to be : — 



Silica 44-94 



Alumina 24*90 



Oxide of iron (with a little 



oxide of manganese) ...... 13*18 



Magnesia 2*64 



Potash 8*94 



Soda 2*06 



Loss by ignition 2*74 



99*40 



The last item answers to a combination of one atom of trisilicate 

 of potash with one atom of protosilicate of alumina. In the un- 

 altered condition of Cordierite, two atoms of bisilicate of magnesia 

 are combined with one atom of protosilicate of alumina. — Proc. Imp. 

 Acad. Vienna, Dec. 11, 1862. 



* Communicated by Count Marschall. 





