20A 



giving the crystal a rough appearance. These hollows 

 agree very well, when narrowly examined, with the shape of" 

 the nucleus. The general form will be better understood by 

 examining the geometrical figure at the bottom, containing a 

 figure of the primitive or rhomboidal prism : see tab. 70 ; 

 allowing for the perspective, and conceiving the sharp angles 

 as the obtuse ones, viz. the right and left hand angles ; the 

 upper and lower faces and the four corners are primitive 

 faces corresponding with the six faces of the nucleus. The 

 four larger octangular faces are evidently parallel to the 

 acute corners of the rhomb (allowing for the perspective). 

 In their formation, the lamina? are (as it were) arranged on 

 the upper and under primitive faces, decreasing from the 

 four acute angles of the nucleus from four obtuse angles ; 

 the same also forming 2 long quadrangular faces at the left 

 hand end, and 2 large hexangular ones at the other end of 

 the geometrical figure coming in contact with the primitive 

 faces at the corners, at an angle of about 123° with the 

 upper or under primitive faces. Next to these, on the 

 same angle of the nucleus, are two other 4-sided faces above 

 and below, the larger at an angle of 140° 5$ 2" upon the 

 primitive, and the. smaller at one of 162° 2' 44 // . These 

 may be distinctly seen on the top of the upper figure. 



The Cumberland specimens seem to have the face of 

 1 23°, which appears not to have been seen by Haiiy. Mr. 

 Hailstone's specimen has two small faces marked by dotted 

 lines on the right hand front corner, and one on the right 

 hand corner at the back, which agree with the faces y of 

 Haiiy. This I have not seen in any other English specimen. 



