64 



(My specimens terminate the radii outwardly, something 

 like Sulphate of Barytes, and seem to be parts of a de- 

 pressed octaedron, sometimes a little truncated : see middle 

 figures.) " Its colour is white in a few cases with a tinge 

 of gray or green, and in some pieces (apparently beginning 

 to decompose) of yellow. Its lustre is silky, some nearly 

 opaque. Its texture is loose." Our upper figure chiefly 

 resembles this description. The lower figure has small 

 dark circles, which seem to be the same substance with the 

 margin darkest. Those larger spreading radii, which con- 

 dense into white opaque circles with the help of smaller 

 stellae, terminate towards the ends. 



The whiter parts are small opaque clusters, in which 

 the three darker ones are imbedded. 



A similar substance has been found near Truro in Corn- 

 wall, which has been examined by the Rev. W. Gregor, of 

 which I hope hereafter to give a figure. 



Mr. Davy's analysis of Hydrargillite : 

 Alumine ... 70 

 Fluid .... 26-2 

 Lime .... 1*4 

 Loss .... 2*4 



100-0 



Upon further examination we find it possible that the 

 crystal may be derived from the cube, as we find the fracture 

 perpendicular to the terminal faces of the right hand figure 

 on a plane with the lengthened sides; and another parallel 

 to the plane of the terminal face. I think I can with a 

 magnifying lens discover a fracture on the sides. The co- 

 lumn or prism is contrary to these faces, forming four sides, 

 and there are two triangular faces set edgewise on the 

 broader angle. We could not measure these faces, but 

 hope that we mav, some time or other, meet with larger 

 crystals fit for that purpose. These faces are often some- 

 what rounded with a rusty sort of decomposition. 



