E. aS. Dana — Chondrodlte from the Tilly- Foster Iron Mine. 75 



In the tables, II, III, IV, are given the angles as measured 

 in a series of crystals (each crystal is numbered). They are import- 

 ant as showing how far the angles are constant. Some considerable 

 variations from calculated angles in a few instances are to be ex- 

 plained by the cause of irregulai'ity already mentioned — the occur- 

 rence of irregular fractures across the planes. In table V are given 

 the su])plement angles calculated for all the planes on e- and also the 

 angles measured on the several crystals (as before numbered). The 

 angles ai-e in pairs corresponding to 201 and iiOl, or 3OI and 201 in 

 each case. (Compare the spherical projection, plate xiii.) 



Table IV. 



Angles measured on C = i-i (010). 



Of the planes which occur, according to Scacchi and vom Rath, on 

 type II of humite, I have identified all but m of Scacchi (f-|) and 

 f-e of vom Rath (f-t). Of new planes I have found the following, 

 which fall in the old vertical or horizontal zones, and many others to 

 be described later; o (;-2'=2]0), r (2-7=021), ia (*-i=047), //3=(|-I= 

 025), ea(f-?=205), r«(|-5=489) ; of these the most interesting is the 

 prism i-2, as hitherto no prism has been found on either the 2d or 3d 

 types. 



Hemihedrism — The ])eculiar hemihedral character of humite has 

 been alluded to, and it is a little striking that the crystals of chon- 

 drodlte should show so entire a corres])ondence to it. Taking the 

 same position for the crystals as vom Rath, r- and r^ appear uni- 

 formly in the positive (or upper) quadrants, r' and r^ always in the 



