88 E. tS. Dana — Chondrodite from the Tilly-Foster Iro7% Mine. 



but some interest in <>• results liave been obtained whicli are described 

 in the closing pages of this paper. 



2. Description of (Jri/stals of Type III. 



Since it was shown by Kokscharow that the Pargas chondrodite 

 was identical with the second tyjie of humite, it was natural to ex- 

 pect that further investigation would prove the existence also of the 

 two remaining types. Up to the present time that expectation has 

 been unfulfilled, and it has been reserved for the Brewster locality to 

 give this confirmation of Scacchi's interesting discovery. The crystals 

 of the 3d type are exceedingly rare, three or four specimens being all 

 that have thus far been foiind, and from these only two individual 

 crystals could be obtained which allowed of measurement. Fortu- 

 nately these two crystals are very satisfactory, bemg small and bril- 

 liant, and establish the fact as well as a hundred could do. Figures 11 

 and 12 show one of the crystals, and figure 13 the other. The appear- 

 ance of the first crystal is best shown in the second of these figures. 

 As will be seen, the planes are the same as in humite, and they are for 

 the most part hemihedral and situated in the same way ; i.e., they in- 

 clude +p',+p', +//, and -p\-~p\—fj\ ^\\(\.—v\-y\-v\—v' as 

 also 1^,1^,1*. Ill the n{v) series the planes are distinct in the negative 

 half, but the crystal is incomjjlete, and it is a little uncertain whether 

 the -|- series should not in part be added in the symmetrical drawing 

 fig. 11; on humite. III, these planes are both positive and negative. 

 No brachydomes are visible, the edge being rounded and rough. ni~ 

 of Scacchi may also be present, but that is a little doubtful. 



The second crystal is of very different form, and Avhile the first was 

 affixed to the rock so that only one-half was developed, this one was 

 imbedded in bnicite, and entirely free in it. It was perfectly formed 

 on all sides, being almost as perfect as the projected drawing, with the 

 exception, however, of the acute (brachydiagonal) edge, which was 

 mostly broken. When only the upper part of the crystal is considered, 

 it will be seen that the hemihedrism is like that in the other case, ex- 

 cept that (f is holohedral. For macrodomes there are /'(f-7^023), 

 z-(l-73=011), /'(2-7— 021), /'(4-7=:041); the last has not been observed 

 on humite. On measuring the planes below it was found that they 

 were not distributed as was expected in accordance with the mono- 

 clinic character of the crystal ; instead, either exti-emity of the brachy- 

 diagonal axis was diffei'ently developed. This is clear in the figure, it 

 being but a more complicated repetition of what was observed in one 



