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Mineralogy and Geology. 127 
ordinary cubical cleavage. The octahedral variety was freely distributed 
among my mineralogical friends, but I was deterred from fulfilling my 
promise to give you a notice of it for publication, from having been told 
that a similar mineral had already been described. Not having been able 
to find any account of an octahedral galena and being assured by you, 
that none such bas been recorded in the numerous works that you have 
consulted, I send you a short notice of the mineral 
It is said to occur in small masses disseminated through limestone, 
and is obtained while quarrying the stone for the purpose of converting it 
into quicklime, The mineral is brittle, like common galena, and the fresh 
Tecently examined by Breithaupt, and noticed by you in the Tenth Sup- 
Plement of Dana’s Mineralogy, were true hexagonal prisms. 
urs truly, J 
New York, Dee. 15th, 1862.” 
In connection with Dr. Torrey’s important observations, it is appropriate 
to quote here the result of some interesting Ee made on this and 
other Varieties of galena communicated to me by Prof. J. P. Cooke, under 
of March 26th, 1862. Prof. Cooke says: “I have at last examined 
the galena, and hasten to send you my preliminary report. 1e- 
dral a is very perfect. I have measured the cleava angles, on a 
m 
Cases merely by the pressure of the finger nail on the acute edges of the 
ng two cube On this I measured the angle 
@ planes at o ite ends, On this | \ 
on the octahedral tle ge planes, equal to 125° 16, although in all 
ir “sé Measurements there is an uncertainty of a few minutes, owing to the 
™perfect reflection of the planes. It then occurred to me that perhaps 
