Sterrett — New Type of Calcite from Joplin, Mo. 75 



a small crystal loaned by Mr. English. It might be consid- 

 ered as made np of two separate individuals grown together 

 in twin position. On each the zone r, t and e appears three 

 times. There was a very small development of the faces of 



the zone r, 31, m and e in their proper positions, though 



these are not shown in the figure. Fig. 3 represents an ideal 



/ mi 



development of a crystal which is given in its natural distor- 

 tion in fig. 4. The G faces were not drawn in fig. 3, since 

 they occur only on one of the twins. As shown in fig. 4, they 

 form an intersection with the twinning plane e, which extends 

 above the line of intersection of the twin crystals. This crys- 

 tal is apparently terminated below by natural r faces parallel 

 to those above and forming an obtuse angle. In most of the 

 crystals a natural termination fails, and its place is occupied 

 by cleavage planes developed when the crystals were detached 

 from the rock. On some crystals the e face is wanting, in 



which caseZ has a larger development, as shown in fig. 5. This 

 represents a large specimen in the Brush collection on which 

 the G faces appear again only on one of the crystals. In this 

 case they form no intersection with the twinning plane, as in 

 fig. 4, but together with r of the upper crystal overlap the 

 lower one, meeting the r of the latter beyond the twinning 



