96 #. S. Dana—Chondrodite jrom the Tilly-Foster Iron Mine. 
far as this half of the crystal goes, have the effect only of 
making it holohedral, giving no re-entrant angles; but, in case 
observed gave for m? Am?, 10° 88’ and 10° 40’ ; required 10° 39’. 
A noteworthy fact in the crystal is the occurrence of the prism 
8 
certainly is, it expresses the exact position of the plane. : 
n interesting crystal is shown in fig. 4. It is conspicu- 
doubt that the planes as given have been determined correctly. 
It is altogether probable that a revolution parallel to the basal 
plane would form an ample explanation of what is observed. 
Chemical composition.—I am glad to be able to add here the 
Scientific School. 
€ material analyzed by Mr. Hawes consisted of fragments 
of crystals of the 2d type, selected with great care to avoid the 
presence of any altered material. It had a deep garnet-red 
color and a brilliant vitreous luster. Its specific gravity, as de- 
termined by Mr. Hawes, was 3-22. Two analyses gave: 
Analysis I Analysis II. 
Silica 34°10 34°05 
Magnesia 53°17 53°72 
Ferrous oxide 717 7-28 
Alumina . 48 “41 
Fluorine 4°14 3°88 
