— 260 Correspondence of J. Nicklés. 
ee general method may be explained by a brief statement of that for white 
corund ; 
Into a carbon crucible put some fluorid of aluminium; and over it 
ject it to a white heat for an hour or so. The vapors of the fluorid and 
boracic acid, meeting in the free space in the crucible over them, decom- — 
pose one another, and afford corundum and fluorid of boron. The crystals 
are rhombohedral with the prismatic and basal planes of a hexagonal — 
prism ; they are optically negative and have all the other physical quali- 
ties of corundum. Large crystals over a centimeter long and very 
have been obtained, but they want thickness. : 
o form the ruby or red corundum, it is only necessary to add a little 
fluorid of chromium to the fluorid of aluminium: and the blue corundum 
or sapphire is obtained under the same circumstances, the only difference 
being that it contains extremely little of chromium in some unknown 
state. With much oxyd of chromium, the corundum is of a fine green 
color. 
by him to the northwest of the locality mentioned by Dr. Shumard, 
between the River Colorado Chiquito (lat. 35° 18’ 43”, long. 110° 49 
56’’), and the Sierra de Magoyon, underlying a series of beds referred to 
different stages of the Trias; the beds were a magnesian limestone and 
f ils is 
en in his report no repre 
Moreover the species of fossils, out 0 
as ta be Oremus, ond We Te 
