44 Scientific Proceedings^ Royal Dublin Society. 



The density of the acicular crystals presented by Professor Hull 

 was found 271, 



That of part of a honey-coloured crystal presented by the same 

 2-71. 



The density of calcspar crystals is given at 2-6 to 2"8. 



And for the purest crystals 2-72. 



Whereas that of similarly pure aragonite crystals varies from 

 2-9 to 3-00. 



It may, therefore, be concluded that from this character alone 

 the crystals in question are calcspars. The further examination of 

 the crystalline forms, cleavage, and hardness, still further confirms 

 this conclusion. The crystals are scratched by aragonite, and the 

 cleavage is very distinctly rhombohedral, and in no way that of 

 aragonite. The crystalline forms are sufficiently distinct in the 

 small acicular crystals to allow of measurement, and are clearly 

 referable to the rhombohedral forms of calcspar. Thus the acicu- 

 lar •crystals show on the sides the zigzag striations characteristic of 

 certain sealenohedral forms and the angles measured on the long, 

 short, and middle edges, give sufficiently approximatively the values 

 corresponding to the sealenohedral form, B12. 



Long edge, calculated angle, 125° 47', found 125° 30'. 

 Short edge, „ „ 114° 50', „ 114° 51'. 



Middle edge, „ ,, 167° 35', „ — 



These crystals are terminated by the forms 



4:R, terminal edge, . . . . 65° 50', 



-2R, „ calculated angle, 78° 51', found 78° 00', 



and R. 



The honey-coloured partial crystal from Cushendall presented 

 by Professor Hull shows the forms 



-512 - 2R, and cleavage terminal forces of R. 



The crystals occurring in the geodes of the iron ore bed present 

 sealenohedral forms oscillating in a remarkable manner, and in the 

 central zone of each face a band, or red stripe strongly marked, 

 and representing the rhombohedral form - 2R. The examination 

 of several of the crystals shows that on either side of this band, 

 itself somewhat rough, there is an oscillation of sealenohedral 



